zig

blob d36bf55e (126076B) - Raw

---

 // SPDX-License-Identifier: MIT
 // Copyright (c) 2015-2020 Zig Contributors
 // This file is part of [zig](https://ziglang.org/), which is MIT licensed.
 // The MIT license requires this copyright notice to be included in all copies
 // and substantial portions of the software.
 const std = @import("../std.zig");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const ast = std.zig.ast;
 const Node = ast.Node;
 const Tree = ast.Tree;
 const AstError = ast.Error;
 const TokenIndex = ast.TokenIndex;
 const NodeIndex = ast.NodeIndex;
 const Token = std.zig.Token;
 
 pub const Error = error{ParseError} || Allocator.Error;
 
 /// Result should be freed with tree.deinit() when there are
 /// no more references to any of the tokens or nodes.
 pub fn parse(gpa: *Allocator, source: []const u8) Allocator.Error!*Tree {
     var token_ids = std.ArrayList(Token.Id).init(gpa);
     defer token_ids.deinit();
     var token_locs = std.ArrayList(Token.Loc).init(gpa);
     defer token_locs.deinit();
 
     // Empirically, the zig std lib has an 8:1 ratio of source bytes to token count.
     const estimated_token_count = source.len / 8;
     try token_ids.ensureCapacity(estimated_token_count);
     try token_locs.ensureCapacity(estimated_token_count);
 
     var tokenizer = std.zig.Tokenizer.init(source);
     while (true) {
         const token = tokenizer.next();
         try token_ids.append(token.id);
         try token_locs.append(token.loc);
         if (token.id == .Eof) break;
     }
 
     var parser: Parser = .{
         .source = source,
         .arena = std.heap.ArenaAllocator.init(gpa),
         .gpa = gpa,
         .token_ids = token_ids.items,
         .token_locs = token_locs.items,
         .errors = .{},
         .tok_i = 0,
     };
     defer parser.errors.deinit(gpa);
     errdefer parser.arena.deinit();
 
     while (token_ids.items[parser.tok_i] == .LineComment) parser.tok_i += 1;
 
     const root_node = try parser.parseRoot();
 
     const tree = try parser.arena.allocator.create(Tree);
     tree.* = .{
         .gpa = gpa,
         .source = source,
         .token_ids = token_ids.toOwnedSlice(),
         .token_locs = token_locs.toOwnedSlice(),
         .errors = parser.errors.toOwnedSlice(gpa),
         .root_node = root_node,
         .arena = parser.arena.state,
     };
     return tree;
 }
 
 /// Represents in-progress parsing, will be converted to an ast.Tree after completion.
 const Parser = struct {
     arena: std.heap.ArenaAllocator,
     gpa: *Allocator,
     source: []const u8,
     token_ids: []const Token.Id,
     token_locs: []const Token.Loc,
     tok_i: TokenIndex,
     errors: std.ArrayListUnmanaged(AstError),
 
     /// Root <- skip ContainerMembers eof
     fn parseRoot(p: *Parser) Allocator.Error!*Node.Root {
         const decls = try parseContainerMembers(p, true);
         defer p.gpa.free(decls);
 
         // parseContainerMembers will try to skip as much
         // invalid tokens as it can so this can only be the EOF
         const eof_token = p.eatToken(.Eof).?;
 
         const decls_len = @intCast(NodeIndex, decls.len);
         const node = try Node.Root.create(&p.arena.allocator, decls_len, eof_token);
         std.mem.copy(*Node, node.decls(), decls);
 
         return node;
     }
 
     /// ContainerMembers
     ///     <- TestDecl ContainerMembers
     ///      / TopLevelComptime ContainerMembers
     ///      / KEYWORD_pub? TopLevelDecl ContainerMembers
     ///      / ContainerField COMMA ContainerMembers
     ///      / ContainerField
     ///      /
     fn parseContainerMembers(p: *Parser, top_level: bool) ![]*Node {
         var list = std.ArrayList(*Node).init(p.gpa);
         defer list.deinit();
 
         var field_state: union(enum) {
             /// no fields have been seen
             none,
             /// currently parsing fields
             seen,
             /// saw fields and then a declaration after them.
             /// payload is first token of previous declaration.
             end: TokenIndex,
             /// ther was a declaration between fields, don't report more errors
             err,
         } = .none;
 
         while (true) {
             if (try p.parseContainerDocComments()) |node| {
                 try list.append(node);
                 continue;
             }
 
             const doc_comments = try p.parseDocComment();
 
             if (p.parseTestDecl() catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ParseError => {
                     p.findNextContainerMember();
                     continue;
                 },
             }) |node| {
                 if (field_state == .seen) {
                     field_state = .{ .end = node.firstToken() };
                 }
                 node.cast(Node.TestDecl).?.doc_comments = doc_comments;
                 try list.append(node);
                 continue;
             }
 
             if (p.parseTopLevelComptime() catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ParseError => {
                     p.findNextContainerMember();
                     continue;
                 },
             }) |node| {
                 if (field_state == .seen) {
                     field_state = .{ .end = node.firstToken() };
                 }
                 node.cast(Node.Comptime).?.doc_comments = doc_comments;
                 try list.append(node);
                 continue;
             }
 
             const visib_token = p.eatToken(.Keyword_pub);
 
             if (p.parseTopLevelDecl(doc_comments, visib_token) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ParseError => {
                     p.findNextContainerMember();
                     continue;
                 },
             }) |node| {
                 if (field_state == .seen) {
                     field_state = .{ .end = visib_token orelse node.firstToken() };
                 }
                 try list.append(node);
                 continue;
             }
 
             if (visib_token != null) {
                 try p.errors.append(p.gpa, .{
                     .ExpectedPubItem = .{ .token = p.tok_i },
                 });
                 // ignore this pub
                 continue;
             }
 
             if (p.parseContainerField() catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ParseError => {
                     // attempt to recover
                     p.findNextContainerMember();
                     continue;
                 },
             }) |node| {
                 switch (field_state) {
                     .none => field_state = .seen,
                     .err, .seen => {},
                     .end => |tok| {
                         try p.errors.append(p.gpa, .{
                             .DeclBetweenFields = .{ .token = tok },
                         });
                         // continue parsing, error will be reported later
                         field_state = .err;
                     },
                 }
 
                 const field = node.cast(Node.ContainerField).?;
                 field.doc_comments = doc_comments;
                 try list.append(node);
                 const comma = p.eatToken(.Comma) orelse {
                     // try to continue parsing
                     const index = p.tok_i;
                     p.findNextContainerMember();
                     const next = p.token_ids[p.tok_i];
                     switch (next) {
                         .Eof => {
                             // no invalid tokens were found
                             if (index == p.tok_i) break;
 
                             // Invalid tokens, add error and exit
                             try p.errors.append(p.gpa, .{
                                 .ExpectedToken = .{ .token = index, .expected_id = .Comma },
                             });
                             break;
                         },
                         else => {
                             if (next == .RBrace) {
                                 if (!top_level) break;
                                 _ = p.nextToken();
                             }
 
                             // add error and continue
                             try p.errors.append(p.gpa, .{
                                 .ExpectedToken = .{ .token = index, .expected_id = .Comma },
                             });
                             continue;
                         },
                     }
                 };
                 if (try p.parseAppendedDocComment(comma)) |appended_comment|
                     field.doc_comments = appended_comment;
                 continue;
             }
 
             // Dangling doc comment
             if (doc_comments != null) {
                 try p.errors.append(p.gpa, .{
                     .UnattachedDocComment = .{ .token = doc_comments.?.firstToken() },
                 });
             }
 
             const next = p.token_ids[p.tok_i];
             switch (next) {
                 .Eof => break,
                 .Keyword_comptime => {
                     _ = p.nextToken();
                     try p.errors.append(p.gpa, .{
                         .ExpectedBlockOrField = .{ .token = p.tok_i },
                     });
                 },
                 else => {
                     const index = p.tok_i;
                     if (next == .RBrace) {
                         if (!top_level) break;
                         _ = p.nextToken();
                     }
 
                     // this was likely not supposed to end yet,
                     // try to find the next declaration
                     p.findNextContainerMember();
                     try p.errors.append(p.gpa, .{
                         .ExpectedContainerMembers = .{ .token = index },
                     });
                 },
             }
         }
 
         return list.toOwnedSlice();
     }
 
     /// Attempts to find next container member by searching for certain tokens
     fn findNextContainerMember(p: *Parser) void {
         var level: u32 = 0;
         while (true) {
             const tok = p.nextToken();
             switch (p.token_ids[tok]) {
                 // any of these can start a new top level declaration
                 .Keyword_test,
                 .Keyword_comptime,
                 .Keyword_pub,
                 .Keyword_export,
                 .Keyword_extern,
                 .Keyword_inline,
                 .Keyword_noinline,
                 .Keyword_usingnamespace,
                 .Keyword_threadlocal,
                 .Keyword_const,
                 .Keyword_var,
                 .Keyword_fn,
                 .Identifier,
                 => {
                     if (level == 0) {
                         p.putBackToken(tok);
                         return;
                     }
                 },
                 .Comma, .Semicolon => {
                     // this decl was likely meant to end here
                     if (level == 0) {
                         return;
                     }
                 },
                 .LParen, .LBracket, .LBrace => level += 1,
                 .RParen, .RBracket => {
                     if (level != 0) level -= 1;
                 },
                 .RBrace => {
                     if (level == 0) {
                         // end of container, exit
                         p.putBackToken(tok);
                         return;
                     }
                     level -= 1;
                 },
                 .Eof => {
                     p.putBackToken(tok);
                     return;
                 },
                 else => {},
             }
         }
     }
 
     /// Attempts to find the next statement by searching for a semicolon
     fn findNextStmt(p: *Parser) void {
         var level: u32 = 0;
         while (true) {
             const tok = p.nextToken();
             switch (p.token_ids[tok]) {
                 .LBrace => level += 1,
                 .RBrace => {
                     if (level == 0) {
                         p.putBackToken(tok);
                         return;
                     }
                     level -= 1;
                 },
                 .Semicolon => {
                     if (level == 0) {
                         return;
                     }
                 },
                 .Eof => {
                     p.putBackToken(tok);
                     return;
                 },
                 else => {},
             }
         }
     }
 
     /// Eat a multiline container doc comment
     fn parseContainerDocComments(p: *Parser) !?*Node {
         if (p.eatToken(.ContainerDocComment)) |first_line| {
             while (p.eatToken(.ContainerDocComment)) |_| {}
             const node = try p.arena.allocator.create(Node.DocComment);
             node.* = .{ .first_line = first_line };
             return &node.base;
         }
         return null;
     }
 
     /// TestDecl <- KEYWORD_test STRINGLITERALSINGLE Block
     fn parseTestDecl(p: *Parser) !?*Node {
         const test_token = p.eatToken(.Keyword_test) orelse return null;
         const name_node = try p.expectNode(parseStringLiteralSingle, .{
             .ExpectedStringLiteral = .{ .token = p.tok_i },
         });
         const block_node = (try p.parseBlock(null)) orelse {
             try p.errors.append(p.gpa, .{ .ExpectedLBrace = .{ .token = p.tok_i } });
             return error.ParseError;
         };
 
         const test_node = try p.arena.allocator.create(Node.TestDecl);
         test_node.* = .{
             .doc_comments = null,
             .test_token = test_token,
             .name = name_node,
             .body_node = block_node,
         };
         return &test_node.base;
     }
 
     /// TopLevelComptime <- KEYWORD_comptime BlockExpr
     fn parseTopLevelComptime(p: *Parser) !?*Node {
         const tok = p.eatToken(.Keyword_comptime) orelse return null;
         const lbrace = p.eatToken(.LBrace) orelse {
             p.putBackToken(tok);
             return null;
         };
         p.putBackToken(lbrace);
         const block_node = try p.expectNode(parseBlockExpr, .{
             .ExpectedLabelOrLBrace = .{ .token = p.tok_i },
         });
 
         const comptime_node = try p.arena.allocator.create(Node.Comptime);
         comptime_node.* = .{
             .doc_comments = null,
             .comptime_token = tok,
             .expr = block_node,
         };
         return &comptime_node.base;
     }
 
     /// TopLevelDecl
     ///     <- (KEYWORD_export / KEYWORD_extern STRINGLITERALSINGLE? / (KEYWORD_inline / KEYWORD_noinline))? FnProto (SEMICOLON / Block)
     ///      / (KEYWORD_export / KEYWORD_extern STRINGLITERALSINGLE?)? KEYWORD_threadlocal? VarDecl
     ///      / KEYWORD_usingnamespace Expr SEMICOLON
     fn parseTopLevelDecl(p: *Parser, doc_comments: ?*Node.DocComment, visib_token: ?TokenIndex) !?*Node {
         var lib_name: ?*Node = null;
         const extern_export_inline_token = blk: {
             if (p.eatToken(.Keyword_export)) |token| break :blk token;
             if (p.eatToken(.Keyword_extern)) |token| {
                 lib_name = try p.parseStringLiteralSingle();
                 break :blk token;
             }
             if (p.eatToken(.Keyword_inline)) |token| break :blk token;
             if (p.eatToken(.Keyword_noinline)) |token| break :blk token;
             break :blk null;
         };
 
         if (try p.parseFnProto(.top_level, .{
             .doc_comments = doc_comments,
             .visib_token = visib_token,
             .extern_export_inline_token = extern_export_inline_token,
             .lib_name = lib_name,
         })) |node| {
             return node;
         }
 
         if (extern_export_inline_token) |token| {
             if (p.token_ids[token] == .Keyword_inline or
                 p.token_ids[token] == .Keyword_noinline)
             {
                 try p.errors.append(p.gpa, .{
                     .ExpectedFn = .{ .token = p.tok_i },
                 });
                 return error.ParseError;
             }
         }
 
         const thread_local_token = p.eatToken(.Keyword_threadlocal);
 
         if (try p.parseVarDecl(.{
             .doc_comments = doc_comments,
             .visib_token = visib_token,
             .thread_local_token = thread_local_token,
             .extern_export_token = extern_export_inline_token,
             .lib_name = lib_name,
         })) |node| {
             return node;
         }
 
         if (thread_local_token != null) {
             try p.errors.append(p.gpa, .{
                 .ExpectedVarDecl = .{ .token = p.tok_i },
             });
             // ignore this and try again;
             return error.ParseError;
         }
 
         if (extern_export_inline_token) |token| {
             try p.errors.append(p.gpa, .{
                 .ExpectedVarDeclOrFn = .{ .token = p.tok_i },
             });
             // ignore this and try again;
             return error.ParseError;
         }
 
         const use_token = p.eatToken(.Keyword_usingnamespace) orelse return null;
         const expr = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         const semicolon_token = try p.expectToken(.Semicolon);
 
         const node = try p.arena.allocator.create(Node.Use);
         node.* = .{
             .doc_comments = doc_comments orelse try p.parseAppendedDocComment(semicolon_token),
             .visib_token = visib_token,
             .use_token = use_token,
             .expr = expr,
             .semicolon_token = semicolon_token,
         };
 
         return &node.base;
     }
 
     /// FnProto <- KEYWORD_fn IDENTIFIER? LPAREN ParamDeclList RPAREN ByteAlign? LinkSection? EXCLAMATIONMARK? (Keyword_anytype / TypeExpr)
     fn parseFnProto(p: *Parser, level: enum { top_level, as_type }, fields: struct {
         doc_comments: ?*Node.DocComment = null,
         visib_token: ?TokenIndex = null,
         extern_export_inline_token: ?TokenIndex = null,
         lib_name: ?*Node = null,
     }) !?*Node {
         // TODO: Remove once extern/async fn rewriting is
         var is_async: ?void = null;
         var is_extern_prototype: ?void = null;
         const cc_token: ?TokenIndex = blk: {
             if (p.eatToken(.Keyword_extern)) |token| {
                 is_extern_prototype = {};
                 break :blk token;
             }
             if (p.eatToken(.Keyword_async)) |token| {
                 is_async = {};
                 break :blk token;
             }
             break :blk null;
         };
         const fn_token = p.eatToken(.Keyword_fn) orelse {
             if (cc_token) |token|
                 p.putBackToken(token);
             return null;
         };
         const name_token = p.eatToken(.Identifier);
         const lparen = try p.expectToken(.LParen);
         const params = try p.parseParamDeclList();
         defer p.gpa.free(params);
         const var_args_token = p.eatToken(.Ellipsis3);
         const rparen = try p.expectToken(.RParen);
         const align_expr = try p.parseByteAlign();
         const section_expr = try p.parseLinkSection();
         const callconv_expr = try p.parseCallconv();
         const exclamation_token = p.eatToken(.Bang);
 
         const return_type_expr = (try p.parseAnyType()) orelse
             try p.expectNodeRecoverable(parseTypeExpr, .{
             // most likely the user forgot to specify the return type.
             // Mark return type as invalid and try to continue.
             .ExpectedReturnType = .{ .token = p.tok_i },
         });
 
         // TODO https://github.com/ziglang/zig/issues/3750
         const R = Node.FnProto.ReturnType;
         const return_type = if (return_type_expr == null)
             R{ .Invalid = rparen }
         else if (exclamation_token != null)
             R{ .InferErrorSet = return_type_expr.? }
         else
             R{ .Explicit = return_type_expr.? };
 
         const body_node: ?*Node = switch (level) {
             .top_level => blk: {
                 if (p.eatToken(.Semicolon)) |_| {
                     break :blk null;
                 }
                 const body_block = (try p.parseBlock(null)) orelse {
                     // Since parseBlock only return error.ParseError on
                     // a missing '}' we can assume this function was
                     // supposed to end here.
                     try p.errors.append(p.gpa, .{ .ExpectedSemiOrLBrace = .{ .token = p.tok_i } });
                     break :blk null;
                 };
                 break :blk body_block;
             },
             .as_type => null,
         };
 
         const fn_proto_node = try Node.FnProto.create(&p.arena.allocator, .{
             .params_len = params.len,
             .fn_token = fn_token,
             .return_type = return_type,
         }, .{
             .doc_comments = fields.doc_comments,
             .visib_token = fields.visib_token,
             .name_token = name_token,
             .var_args_token = var_args_token,
             .extern_export_inline_token = fields.extern_export_inline_token,
             .body_node = body_node,
             .lib_name = fields.lib_name,
             .align_expr = align_expr,
             .section_expr = section_expr,
             .callconv_expr = callconv_expr,
             .is_extern_prototype = is_extern_prototype,
             .is_async = is_async,
         });
         std.mem.copy(Node.FnProto.ParamDecl, fn_proto_node.params(), params);
 
         return &fn_proto_node.base;
     }
 
     /// VarDecl <- (KEYWORD_const / KEYWORD_var) IDENTIFIER (COLON TypeExpr)? ByteAlign? LinkSection? (EQUAL Expr)? SEMICOLON
     fn parseVarDecl(p: *Parser, fields: struct {
         doc_comments: ?*Node.DocComment = null,
         visib_token: ?TokenIndex = null,
         thread_local_token: ?TokenIndex = null,
         extern_export_token: ?TokenIndex = null,
         lib_name: ?*Node = null,
         comptime_token: ?TokenIndex = null,
     }) !?*Node {
         const mut_token = p.eatToken(.Keyword_const) orelse
             p.eatToken(.Keyword_var) orelse
             return null;
 
         const name_token = try p.expectToken(.Identifier);
         const type_node = if (p.eatToken(.Colon) != null)
             try p.expectNode(parseTypeExpr, .{
                 .ExpectedTypeExpr = .{ .token = p.tok_i },
             })
         else
             null;
         const align_node = try p.parseByteAlign();
         const section_node = try p.parseLinkSection();
         const eq_token = p.eatToken(.Equal);
         const init_node = if (eq_token != null) blk: {
             break :blk try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
         } else null;
         const semicolon_token = try p.expectToken(.Semicolon);
 
         const doc_comments = fields.doc_comments orelse try p.parseAppendedDocComment(semicolon_token);
 
         const node = try Node.VarDecl.create(&p.arena.allocator, .{
             .mut_token = mut_token,
             .name_token = name_token,
             .semicolon_token = semicolon_token,
         }, .{
             .doc_comments = doc_comments,
             .visib_token = fields.visib_token,
             .thread_local_token = fields.thread_local_token,
             .eq_token = eq_token,
             .comptime_token = fields.comptime_token,
             .extern_export_token = fields.extern_export_token,
             .lib_name = fields.lib_name,
             .type_node = type_node,
             .align_node = align_node,
             .section_node = section_node,
             .init_node = init_node,
         });
         return &node.base;
     }
 
     /// ContainerField <- KEYWORD_comptime? IDENTIFIER (COLON TypeExpr ByteAlign?)? (EQUAL Expr)?
     fn parseContainerField(p: *Parser) !?*Node {
         const comptime_token = p.eatToken(.Keyword_comptime);
         const name_token = p.eatToken(.Identifier) orelse {
             if (comptime_token) |t| p.putBackToken(t);
             return null;
         };
 
         var align_expr: ?*Node = null;
         var type_expr: ?*Node = null;
         if (p.eatToken(.Colon)) |_| {
             if (p.eatToken(.Keyword_anytype) orelse p.eatToken(.Keyword_var)) |anytype_tok| {
                 const node = try p.arena.allocator.create(Node.OneToken);
                 node.* = .{
                     .base = .{ .tag = .AnyType },
                     .token = anytype_tok,
                 };
                 type_expr = &node.base;
             } else {
                 type_expr = try p.expectNode(parseTypeExpr, .{
                     .ExpectedTypeExpr = .{ .token = p.tok_i },
                 });
                 align_expr = try p.parseByteAlign();
             }
         }
 
         const value_expr = if (p.eatToken(.Equal)) |_|
             try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             })
         else
             null;
 
         const node = try p.arena.allocator.create(Node.ContainerField);
         node.* = .{
             .doc_comments = null,
             .comptime_token = comptime_token,
             .name_token = name_token,
             .type_expr = type_expr,
             .value_expr = value_expr,
             .align_expr = align_expr,
         };
         return &node.base;
     }
 
     /// Statement
     ///     <- KEYWORD_comptime? VarDecl
     ///      / KEYWORD_comptime BlockExprStatement
     ///      / KEYWORD_nosuspend BlockExprStatement
     ///      / KEYWORD_suspend (SEMICOLON / BlockExprStatement)
     ///      / KEYWORD_defer BlockExprStatement
     ///      / KEYWORD_errdefer Payload? BlockExprStatement
     ///      / IfStatement
     ///      / LabeledStatement
     ///      / SwitchExpr
     ///      / AssignExpr SEMICOLON
     fn parseStatement(p: *Parser) Error!?*Node {
         const comptime_token = p.eatToken(.Keyword_comptime);
 
         if (try p.parseVarDecl(.{
             .comptime_token = comptime_token,
         })) |node| {
             return node;
         }
 
         if (comptime_token) |token| {
             const block_expr = try p.expectNode(parseBlockExprStatement, .{
                 .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
             });
 
             const node = try p.arena.allocator.create(Node.Comptime);
             node.* = .{
                 .doc_comments = null,
                 .comptime_token = token,
                 .expr = block_expr,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_nosuspend)) |nosuspend_token| {
             const block_expr = try p.expectNode(parseBlockExprStatement, .{
                 .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
             });
 
             const node = try p.arena.allocator.create(Node.Nosuspend);
             node.* = .{
                 .nosuspend_token = nosuspend_token,
                 .expr = block_expr,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_suspend)) |suspend_token| {
             const semicolon = p.eatToken(.Semicolon);
 
             const body_node = if (semicolon == null) blk: {
                 break :blk try p.expectNode(parseBlockExprStatement, .{
                     .ExpectedBlockOrExpression = .{ .token = p.tok_i },
                 });
             } else null;
 
             const node = try p.arena.allocator.create(Node.Suspend);
             node.* = .{
                 .suspend_token = suspend_token,
                 .body = body_node,
             };
             return &node.base;
         }
 
         const defer_token = p.eatToken(.Keyword_defer) orelse p.eatToken(.Keyword_errdefer);
         if (defer_token) |token| {
             const payload = if (p.token_ids[token] == .Keyword_errdefer)
                 try p.parsePayload()
             else
                 null;
             const expr_node = try p.expectNode(parseBlockExprStatement, .{
                 .ExpectedBlockOrExpression = .{ .token = p.tok_i },
             });
             const node = try p.arena.allocator.create(Node.Defer);
             node.* = .{
                 .defer_token = token,
                 .expr = expr_node,
                 .payload = payload,
             };
             return &node.base;
         }
 
         if (try p.parseIfStatement()) |node| return node;
         if (try p.parseLabeledStatement()) |node| return node;
         if (try p.parseSwitchExpr()) |node| return node;
         if (try p.parseAssignExpr()) |node| {
             _ = try p.expectTokenRecoverable(.Semicolon);
             return node;
         }
 
         return null;
     }
 
     /// IfStatement
     ///     <- IfPrefix BlockExpr ( KEYWORD_else Payload? Statement )?
     ///      / IfPrefix AssignExpr ( SEMICOLON / KEYWORD_else Payload? Statement )
     fn parseIfStatement(p: *Parser) !?*Node {
         const if_node = (try p.parseIfPrefix()) orelse return null;
         const if_prefix = if_node.cast(Node.If).?;
 
         const block_expr = (try p.parseBlockExpr());
         const assign_expr = if (block_expr == null)
             try p.expectNode(parseAssignExpr, .{
                 .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
             })
         else
             null;
 
         const semicolon = if (assign_expr != null) p.eatToken(.Semicolon) else null;
 
         const else_node = if (semicolon == null) blk: {
             const else_token = p.eatToken(.Keyword_else) orelse break :blk null;
             const payload = try p.parsePayload();
             const else_body = try p.expectNode(parseStatement, .{
                 .InvalidToken = .{ .token = p.tok_i },
             });
 
             const node = try p.arena.allocator.create(Node.Else);
             node.* = .{
                 .else_token = else_token,
                 .payload = payload,
                 .body = else_body,
             };
 
             break :blk node;
         } else null;
 
         if (block_expr) |body| {
             if_prefix.body = body;
             if_prefix.@"else" = else_node;
             return if_node;
         }
 
         if (assign_expr) |body| {
             if_prefix.body = body;
             if (semicolon != null) return if_node;
             if (else_node != null) {
                 if_prefix.@"else" = else_node;
                 return if_node;
             }
             try p.errors.append(p.gpa, .{
                 .ExpectedSemiOrElse = .{ .token = p.tok_i },
             });
         }
 
         return if_node;
     }
 
     /// LabeledStatement <- BlockLabel? (Block / LoopStatement)
     fn parseLabeledStatement(p: *Parser) !?*Node {
         var colon: TokenIndex = undefined;
         const label_token = p.parseBlockLabel(&colon);
 
         if (try p.parseBlock(label_token)) |node| return node;
 
         if (try p.parseLoopStatement()) |node| {
             if (node.cast(Node.For)) |for_node| {
                 for_node.label = label_token;
             } else if (node.cast(Node.While)) |while_node| {
                 while_node.label = label_token;
             } else unreachable;
             return node;
         }
 
         if (label_token != null) {
             try p.errors.append(p.gpa, .{
                 .ExpectedLabelable = .{ .token = p.tok_i },
             });
             return error.ParseError;
         }
 
         return null;
     }
 
     /// LoopStatement <- KEYWORD_inline? (ForStatement / WhileStatement)
     fn parseLoopStatement(p: *Parser) !?*Node {
         const inline_token = p.eatToken(.Keyword_inline);
 
         if (try p.parseForStatement()) |node| {
             node.cast(Node.For).?.inline_token = inline_token;
             return node;
         }
 
         if (try p.parseWhileStatement()) |node| {
             node.cast(Node.While).?.inline_token = inline_token;
             return node;
         }
         if (inline_token == null) return null;
 
         // If we've seen "inline", there should have been a "for" or "while"
         try p.errors.append(p.gpa, .{
             .ExpectedInlinable = .{ .token = p.tok_i },
         });
         return error.ParseError;
     }
 
     /// ForStatement
     ///     <- ForPrefix BlockExpr ( KEYWORD_else Statement )?
     ///      / ForPrefix AssignExpr ( SEMICOLON / KEYWORD_else Statement )
     fn parseForStatement(p: *Parser) !?*Node {
         const node = (try p.parseForPrefix()) orelse return null;
         const for_prefix = node.cast(Node.For).?;
 
         if (try p.parseBlockExpr()) |block_expr_node| {
             for_prefix.body = block_expr_node;
 
             if (p.eatToken(.Keyword_else)) |else_token| {
                 const statement_node = try p.expectNode(parseStatement, .{
                     .InvalidToken = .{ .token = p.tok_i },
                 });
 
                 const else_node = try p.arena.allocator.create(Node.Else);
                 else_node.* = .{
                     .else_token = else_token,
                     .payload = null,
                     .body = statement_node,
                 };
                 for_prefix.@"else" = else_node;
 
                 return node;
             }
 
             return node;
         }
 
         for_prefix.body = try p.expectNode(parseAssignExpr, .{
             .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
         });
 
         if (p.eatToken(.Semicolon) != null) return node;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const statement_node = try p.expectNode(parseStatement, .{
                 .ExpectedStatement = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = null,
                 .body = statement_node,
             };
             for_prefix.@"else" = else_node;
             return node;
         }
 
         try p.errors.append(p.gpa, .{
             .ExpectedSemiOrElse = .{ .token = p.tok_i },
         });
 
         return node;
     }
 
     /// WhileStatement
     ///     <- WhilePrefix BlockExpr ( KEYWORD_else Payload? Statement )?
     ///      / WhilePrefix AssignExpr ( SEMICOLON / KEYWORD_else Payload? Statement )
     fn parseWhileStatement(p: *Parser) !?*Node {
         const node = (try p.parseWhilePrefix()) orelse return null;
         const while_prefix = node.cast(Node.While).?;
 
         if (try p.parseBlockExpr()) |block_expr_node| {
             while_prefix.body = block_expr_node;
 
             if (p.eatToken(.Keyword_else)) |else_token| {
                 const payload = try p.parsePayload();
 
                 const statement_node = try p.expectNode(parseStatement, .{
                     .InvalidToken = .{ .token = p.tok_i },
                 });
 
                 const else_node = try p.arena.allocator.create(Node.Else);
                 else_node.* = .{
                     .else_token = else_token,
                     .payload = payload,
                     .body = statement_node,
                 };
                 while_prefix.@"else" = else_node;
 
                 return node;
             }
 
             return node;
         }
 
         while_prefix.body = try p.expectNode(parseAssignExpr, .{
             .ExpectedBlockOrAssignment = .{ .token = p.tok_i },
         });
 
         if (p.eatToken(.Semicolon) != null) return node;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const payload = try p.parsePayload();
 
             const statement_node = try p.expectNode(parseStatement, .{
                 .ExpectedStatement = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = payload,
                 .body = statement_node,
             };
             while_prefix.@"else" = else_node;
             return node;
         }
 
         try p.errors.append(p.gpa, .{
             .ExpectedSemiOrElse = .{ .token = p.tok_i },
         });
 
         return node;
     }
 
     /// BlockExprStatement
     ///     <- BlockExpr
     ///      / AssignExpr SEMICOLON
     fn parseBlockExprStatement(p: *Parser) !?*Node {
         if (try p.parseBlockExpr()) |node| return node;
         if (try p.parseAssignExpr()) |node| {
             _ = try p.expectTokenRecoverable(.Semicolon);
             return node;
         }
         return null;
     }
 
     /// BlockExpr <- BlockLabel? Block
     fn parseBlockExpr(p: *Parser) Error!?*Node {
         var colon: TokenIndex = undefined;
         const label_token = p.parseBlockLabel(&colon);
         const block_node = (try p.parseBlock(label_token)) orelse {
             if (label_token) |label| {
                 p.putBackToken(label + 1); // ":"
                 p.putBackToken(label); // IDENTIFIER
             }
             return null;
         };
         return block_node;
     }
 
     /// AssignExpr <- Expr (AssignOp Expr)?
     fn parseAssignExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseAssignOp, parseExpr, .Once);
     }
 
     /// Expr <- KEYWORD_try* BoolOrExpr
     fn parseExpr(p: *Parser) Error!?*Node {
         return p.parsePrefixOpExpr(parseTry, parseBoolOrExpr);
     }
 
     /// BoolOrExpr <- BoolAndExpr (KEYWORD_or BoolAndExpr)*
     fn parseBoolOrExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(
             SimpleBinOpParseFn(.Keyword_or, .BoolOr),
             parseBoolAndExpr,
             .Infinitely,
         );
     }
 
     /// BoolAndExpr <- CompareExpr (KEYWORD_and CompareExpr)*
     fn parseBoolAndExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(
             SimpleBinOpParseFn(.Keyword_and, .BoolAnd),
             parseCompareExpr,
             .Infinitely,
         );
     }
 
     /// CompareExpr <- BitwiseExpr (CompareOp BitwiseExpr)?
     fn parseCompareExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseCompareOp, parseBitwiseExpr, .Once);
     }
 
     /// BitwiseExpr <- BitShiftExpr (BitwiseOp BitShiftExpr)*
     fn parseBitwiseExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseBitwiseOp, parseBitShiftExpr, .Infinitely);
     }
 
     /// BitShiftExpr <- AdditionExpr (BitShiftOp AdditionExpr)*
     fn parseBitShiftExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseBitShiftOp, parseAdditionExpr, .Infinitely);
     }
 
     /// AdditionExpr <- MultiplyExpr (AdditionOp MultiplyExpr)*
     fn parseAdditionExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseAdditionOp, parseMultiplyExpr, .Infinitely);
     }
 
     /// MultiplyExpr <- PrefixExpr (MultiplyOp PrefixExpr)*
     fn parseMultiplyExpr(p: *Parser) !?*Node {
         return p.parseBinOpExpr(parseMultiplyOp, parsePrefixExpr, .Infinitely);
     }
 
     /// PrefixExpr <- PrefixOp* PrimaryExpr
     fn parsePrefixExpr(p: *Parser) !?*Node {
         return p.parsePrefixOpExpr(parsePrefixOp, parsePrimaryExpr);
     }
 
     /// PrimaryExpr
     ///     <- AsmExpr
     ///      / IfExpr
     ///      / KEYWORD_break BreakLabel? Expr?
     ///      / KEYWORD_comptime Expr
     ///      / KEYWORD_nosuspend Expr
     ///      / KEYWORD_continue BreakLabel?
     ///      / KEYWORD_resume Expr
     ///      / KEYWORD_return Expr?
     ///      / BlockLabel? LoopExpr
     ///      / Block
     ///      / CurlySuffixExpr
     fn parsePrimaryExpr(p: *Parser) !?*Node {
         if (try p.parseAsmExpr()) |node| return node;
         if (try p.parseIfExpr()) |node| return node;
 
         if (p.eatToken(.Keyword_break)) |token| {
             const label = try p.parseBreakLabel();
             const expr_node = try p.parseExpr();
             const node = try Node.ControlFlowExpression.create(&p.arena.allocator, .{
                 .tag = .Break,
                 .ltoken = token,
             }, .{
                 .label = label,
                 .rhs = expr_node,
             });
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_comptime)) |token| {
             const expr_node = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
             const node = try p.arena.allocator.create(Node.Comptime);
             node.* = .{
                 .doc_comments = null,
                 .comptime_token = token,
                 .expr = expr_node,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_nosuspend)) |token| {
             const expr_node = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
             const node = try p.arena.allocator.create(Node.Nosuspend);
             node.* = .{
                 .nosuspend_token = token,
                 .expr = expr_node,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_continue)) |token| {
             const label = try p.parseBreakLabel();
             const node = try Node.ControlFlowExpression.create(&p.arena.allocator, .{
                 .tag = .Continue,
                 .ltoken = token,
             }, .{
                 .label = label,
                 .rhs = null,
             });
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_resume)) |token| {
             const expr_node = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
             const node = try p.arena.allocator.create(Node.SimplePrefixOp);
             node.* = .{
                 .base = .{ .tag = .Resume },
                 .op_token = token,
                 .rhs = expr_node,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_return)) |token| {
             const expr_node = try p.parseExpr();
             const node = try Node.ControlFlowExpression.create(&p.arena.allocator, .{
                 .tag = .Return,
                 .ltoken = token,
             }, .{
                 .rhs = expr_node,
             });
             return &node.base;
         }
 
         var colon: TokenIndex = undefined;
         const label = p.parseBlockLabel(&colon);
         if (try p.parseLoopExpr()) |node| {
             if (node.cast(Node.For)) |for_node| {
                 for_node.label = label;
             } else if (node.cast(Node.While)) |while_node| {
                 while_node.label = label;
             } else unreachable;
             return node;
         }
         if (label) |token| {
             p.putBackToken(token + 1); // ":"
             p.putBackToken(token); // IDENTIFIER
         }
 
         if (try p.parseBlock(null)) |node| return node;
         if (try p.parseCurlySuffixExpr()) |node| return node;
 
         return null;
     }
 
     /// IfExpr <- IfPrefix Expr (KEYWORD_else Payload? Expr)?
     fn parseIfExpr(p: *Parser) !?*Node {
         return p.parseIf(parseExpr);
     }
 
     /// Block <- LBRACE Statement* RBRACE
     fn parseBlock(p: *Parser, label_token: ?TokenIndex) !?*Node {
         const lbrace = p.eatToken(.LBrace) orelse return null;
 
         var statements = std.ArrayList(*Node).init(p.gpa);
         defer statements.deinit();
 
         while (true) {
             const statement = (p.parseStatement() catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ParseError => {
                     // try to skip to the next statement
                     p.findNextStmt();
                     continue;
                 },
             }) orelse break;
             try statements.append(statement);
         }
 
         const rbrace = try p.expectToken(.RBrace);
 
         const statements_len = @intCast(NodeIndex, statements.items.len);
 
         if (label_token) |label| {
             const block_node = try Node.LabeledBlock.alloc(&p.arena.allocator, statements_len);
             block_node.* = .{
                 .label = label,
                 .lbrace = lbrace,
                 .statements_len = statements_len,
                 .rbrace = rbrace,
             };
             std.mem.copy(*Node, block_node.statements(), statements.items);
             return &block_node.base;
         } else {
             const block_node = try Node.Block.alloc(&p.arena.allocator, statements_len);
             block_node.* = .{
                 .lbrace = lbrace,
                 .statements_len = statements_len,
                 .rbrace = rbrace,
             };
             std.mem.copy(*Node, block_node.statements(), statements.items);
             return &block_node.base;
         }
     }
 
     /// LoopExpr <- KEYWORD_inline? (ForExpr / WhileExpr)
     fn parseLoopExpr(p: *Parser) !?*Node {
         const inline_token = p.eatToken(.Keyword_inline);
 
         if (try p.parseForExpr()) |node| {
             node.cast(Node.For).?.inline_token = inline_token;
             return node;
         }
 
         if (try p.parseWhileExpr()) |node| {
             node.cast(Node.While).?.inline_token = inline_token;
             return node;
         }
 
         if (inline_token == null) return null;
 
         // If we've seen "inline", there should have been a "for" or "while"
         try p.errors.append(p.gpa, .{
             .ExpectedInlinable = .{ .token = p.tok_i },
         });
         return error.ParseError;
     }
 
     /// ForExpr <- ForPrefix Expr (KEYWORD_else Expr)?
     fn parseForExpr(p: *Parser) !?*Node {
         const node = (try p.parseForPrefix()) orelse return null;
         const for_prefix = node.cast(Node.For).?;
 
         const body_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         for_prefix.body = body_node;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const body = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = null,
                 .body = body,
             };
 
             for_prefix.@"else" = else_node;
         }
 
         return node;
     }
 
     /// WhileExpr <- WhilePrefix Expr (KEYWORD_else Payload? Expr)?
     fn parseWhileExpr(p: *Parser) !?*Node {
         const node = (try p.parseWhilePrefix()) orelse return null;
         const while_prefix = node.cast(Node.While).?;
 
         const body_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         while_prefix.body = body_node;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const payload = try p.parsePayload();
             const body = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = payload,
                 .body = body,
             };
 
             while_prefix.@"else" = else_node;
         }
 
         return node;
     }
 
     /// CurlySuffixExpr <- TypeExpr InitList?
     fn parseCurlySuffixExpr(p: *Parser) !?*Node {
         const lhs = (try p.parseTypeExpr()) orelse return null;
         const suffix_op = (try p.parseInitList(lhs)) orelse return lhs;
         return suffix_op;
     }
 
     /// InitList
     ///     <- LBRACE FieldInit (COMMA FieldInit)* COMMA? RBRACE
     ///      / LBRACE Expr (COMMA Expr)* COMMA? RBRACE
     ///      / LBRACE RBRACE
     fn parseInitList(p: *Parser, lhs: *Node) !?*Node {
         const lbrace = p.eatToken(.LBrace) orelse return null;
         var init_list = std.ArrayList(*Node).init(p.gpa);
         defer init_list.deinit();
 
         if (try p.parseFieldInit()) |field_init| {
             try init_list.append(field_init);
             while (p.eatToken(.Comma)) |_| {
                 const next = (try p.parseFieldInit()) orelse break;
                 try init_list.append(next);
             }
             const node = try Node.StructInitializer.alloc(&p.arena.allocator, init_list.items.len);
             node.* = .{
                 .lhs = lhs,
                 .rtoken = try p.expectToken(.RBrace),
                 .list_len = init_list.items.len,
             };
             std.mem.copy(*Node, node.list(), init_list.items);
             return &node.base;
         }
 
         if (try p.parseExpr()) |expr| {
             try init_list.append(expr);
             while (p.eatToken(.Comma)) |_| {
                 const next = (try p.parseExpr()) orelse break;
                 try init_list.append(next);
             }
             const node = try Node.ArrayInitializer.alloc(&p.arena.allocator, init_list.items.len);
             node.* = .{
                 .lhs = lhs,
                 .rtoken = try p.expectToken(.RBrace),
                 .list_len = init_list.items.len,
             };
             std.mem.copy(*Node, node.list(), init_list.items);
             return &node.base;
         }
 
         const node = try p.arena.allocator.create(Node.StructInitializer);
         node.* = .{
             .lhs = lhs,
             .rtoken = try p.expectToken(.RBrace),
             .list_len = 0,
         };
         return &node.base;
     }
 
     /// InitList
     ///     <- LBRACE FieldInit (COMMA FieldInit)* COMMA? RBRACE
     ///      / LBRACE Expr (COMMA Expr)* COMMA? RBRACE
     ///      / LBRACE RBRACE
     fn parseAnonInitList(p: *Parser, dot: TokenIndex) !?*Node {
         const lbrace = p.eatToken(.LBrace) orelse return null;
         var init_list = std.ArrayList(*Node).init(p.gpa);
         defer init_list.deinit();
 
         if (try p.parseFieldInit()) |field_init| {
             try init_list.append(field_init);
             while (p.eatToken(.Comma)) |_| {
                 const next = (try p.parseFieldInit()) orelse break;
                 try init_list.append(next);
             }
             const node = try Node.StructInitializerDot.alloc(&p.arena.allocator, init_list.items.len);
             node.* = .{
                 .dot = dot,
                 .rtoken = try p.expectToken(.RBrace),
                 .list_len = init_list.items.len,
             };
             std.mem.copy(*Node, node.list(), init_list.items);
             return &node.base;
         }
 
         if (try p.parseExpr()) |expr| {
             try init_list.append(expr);
             while (p.eatToken(.Comma)) |_| {
                 const next = (try p.parseExpr()) orelse break;
                 try init_list.append(next);
             }
             const node = try Node.ArrayInitializerDot.alloc(&p.arena.allocator, init_list.items.len);
             node.* = .{
                 .dot = dot,
                 .rtoken = try p.expectToken(.RBrace),
                 .list_len = init_list.items.len,
             };
             std.mem.copy(*Node, node.list(), init_list.items);
             return &node.base;
         }
 
         const node = try p.arena.allocator.create(Node.StructInitializerDot);
         node.* = .{
             .dot = dot,
             .rtoken = try p.expectToken(.RBrace),
             .list_len = 0,
         };
         return &node.base;
     }
 
     /// TypeExpr <- PrefixTypeOp* ErrorUnionExpr
     fn parseTypeExpr(p: *Parser) Error!?*Node {
         return p.parsePrefixOpExpr(parsePrefixTypeOp, parseErrorUnionExpr);
     }
 
     /// ErrorUnionExpr <- SuffixExpr (EXCLAMATIONMARK TypeExpr)?
     fn parseErrorUnionExpr(p: *Parser) !?*Node {
         const suffix_expr = (try p.parseSuffixExpr()) orelse return null;
 
         if (try SimpleBinOpParseFn(.Bang, .ErrorUnion)(p)) |node| {
             const error_union = node.castTag(.ErrorUnion).?;
             const type_expr = try p.expectNode(parseTypeExpr, .{
                 .ExpectedTypeExpr = .{ .token = p.tok_i },
             });
             error_union.lhs = suffix_expr;
             error_union.rhs = type_expr;
             return node;
         }
 
         return suffix_expr;
     }
 
     /// SuffixExpr
     ///     <- KEYWORD_async PrimaryTypeExpr SuffixOp* FnCallArguments
     ///      / PrimaryTypeExpr (SuffixOp / FnCallArguments)*
     fn parseSuffixExpr(p: *Parser) !?*Node {
         const maybe_async = p.eatToken(.Keyword_async);
         if (maybe_async) |async_token| {
             const token_fn = p.eatToken(.Keyword_fn);
             if (token_fn != null) {
                 // TODO: remove this hack when async fn rewriting is
                 // HACK: If we see the keyword `fn`, then we assume that
                 //       we are parsing an async fn proto, and not a call.
                 //       We therefore put back all tokens consumed by the async
                 //       prefix...
                 p.putBackToken(token_fn.?);
                 p.putBackToken(async_token);
                 return p.parsePrimaryTypeExpr();
             }
             var res = try p.expectNode(parsePrimaryTypeExpr, .{
                 .ExpectedPrimaryTypeExpr = .{ .token = p.tok_i },
             });
 
             while (try p.parseSuffixOp(res)) |node| {
                 res = node;
             }
 
             const params = (try p.parseFnCallArguments()) orelse {
                 try p.errors.append(p.gpa, .{
                     .ExpectedParamList = .{ .token = p.tok_i },
                 });
                 // ignore this, continue parsing
                 return res;
             };
             defer p.gpa.free(params.list);
             const node = try Node.Call.alloc(&p.arena.allocator, params.list.len);
             node.* = .{
                 .lhs = res,
                 .params_len = params.list.len,
                 .async_token = async_token,
                 .rtoken = params.rparen,
             };
             std.mem.copy(*Node, node.params(), params.list);
             return &node.base;
         }
         if (try p.parsePrimaryTypeExpr()) |expr| {
             var res = expr;
 
             while (true) {
                 if (try p.parseSuffixOp(res)) |node| {
                     res = node;
                     continue;
                 }
                 if (try p.parseFnCallArguments()) |params| {
                     defer p.gpa.free(params.list);
                     const call = try Node.Call.alloc(&p.arena.allocator, params.list.len);
                     call.* = .{
                         .lhs = res,
                         .params_len = params.list.len,
                         .async_token = null,
                         .rtoken = params.rparen,
                     };
                     std.mem.copy(*Node, call.params(), params.list);
                     res = &call.base;
                     continue;
                 }
                 break;
             }
             return res;
         }
 
         return null;
     }
 
     /// PrimaryTypeExpr
     ///     <- BUILTINIDENTIFIER FnCallArguments
     ///      / CHAR_LITERAL
     ///      / ContainerDecl
     ///      / DOT IDENTIFIER
     ///      / ErrorSetDecl
     ///      / FLOAT
     ///      / FnProto
     ///      / GroupedExpr
     ///      / LabeledTypeExpr
     ///      / IDENTIFIER
     ///      / IfTypeExpr
     ///      / INTEGER
     ///      / KEYWORD_comptime TypeExpr
     ///      / KEYWORD_error DOT IDENTIFIER
     ///      / KEYWORD_false
     ///      / KEYWORD_null
     ///      / KEYWORD_anyframe
     ///      / KEYWORD_true
     ///      / KEYWORD_undefined
     ///      / KEYWORD_unreachable
     ///      / STRINGLITERAL
     ///      / SwitchExpr
     fn parsePrimaryTypeExpr(p: *Parser) !?*Node {
         if (try p.parseBuiltinCall()) |node| return node;
         if (p.eatToken(.CharLiteral)) |token| {
             const node = try p.arena.allocator.create(Node.OneToken);
             node.* = .{
                 .base = .{ .tag = .CharLiteral },
                 .token = token,
             };
             return &node.base;
         }
         if (try p.parseContainerDecl()) |node| return node;
         if (try p.parseAnonLiteral()) |node| return node;
         if (try p.parseErrorSetDecl()) |node| return node;
         if (try p.parseFloatLiteral()) |node| return node;
         if (try p.parseFnProto(.as_type, .{})) |node| return node;
         if (try p.parseGroupedExpr()) |node| return node;
         if (try p.parseLabeledTypeExpr()) |node| return node;
         if (try p.parseIdentifier()) |node| return node;
         if (try p.parseIfTypeExpr()) |node| return node;
         if (try p.parseIntegerLiteral()) |node| return node;
         if (p.eatToken(.Keyword_comptime)) |token| {
             const expr = (try p.parseTypeExpr()) orelse return null;
             const node = try p.arena.allocator.create(Node.Comptime);
             node.* = .{
                 .doc_comments = null,
                 .comptime_token = token,
                 .expr = expr,
             };
             return &node.base;
         }
         if (p.eatToken(.Keyword_error)) |token| {
             const period = try p.expectTokenRecoverable(.Period);
             const identifier = try p.expectNodeRecoverable(parseIdentifier, .{
                 .ExpectedIdentifier = .{ .token = p.tok_i },
             });
             const global_error_set = try p.createLiteral(.ErrorType, token);
             if (period == null or identifier == null) return global_error_set;
 
             const node = try p.arena.allocator.create(Node.SimpleInfixOp);
             node.* = .{
                 .base = Node{ .tag = .Period },
                 .op_token = period.?,
                 .lhs = global_error_set,
                 .rhs = identifier.?,
             };
             return &node.base;
         }
         if (p.eatToken(.Keyword_false)) |token| return p.createLiteral(.BoolLiteral, token);
         if (p.eatToken(.Keyword_null)) |token| return p.createLiteral(.NullLiteral, token);
         if (p.eatToken(.Keyword_anyframe)) |token| {
             const node = try p.arena.allocator.create(Node.AnyFrameType);
             node.* = .{
                 .anyframe_token = token,
                 .result = null,
             };
             return &node.base;
         }
         if (p.eatToken(.Keyword_true)) |token| return p.createLiteral(.BoolLiteral, token);
         if (p.eatToken(.Keyword_undefined)) |token| return p.createLiteral(.UndefinedLiteral, token);
         if (p.eatToken(.Keyword_unreachable)) |token| return p.createLiteral(.Unreachable, token);
         if (try p.parseStringLiteral()) |node| return node;
         if (try p.parseSwitchExpr()) |node| return node;
 
         return null;
     }
 
     /// ContainerDecl <- (KEYWORD_extern / KEYWORD_packed)? ContainerDeclAuto
     fn parseContainerDecl(p: *Parser) !?*Node {
         const layout_token = p.eatToken(.Keyword_extern) orelse
             p.eatToken(.Keyword_packed);
 
         const node = (try p.parseContainerDeclAuto()) orelse {
             if (layout_token) |token|
                 p.putBackToken(token);
             return null;
         };
         node.cast(Node.ContainerDecl).?.*.layout_token = layout_token;
         return node;
     }
 
     /// ErrorSetDecl <- KEYWORD_error LBRACE IdentifierList RBRACE
     fn parseErrorSetDecl(p: *Parser) !?*Node {
         const error_token = p.eatToken(.Keyword_error) orelse return null;
         if (p.eatToken(.LBrace) == null) {
             // Might parse as `KEYWORD_error DOT IDENTIFIER` later in PrimaryTypeExpr, so don't error
             p.putBackToken(error_token);
             return null;
         }
         const decls = try p.parseErrorTagList();
         defer p.gpa.free(decls);
         const rbrace = try p.expectToken(.RBrace);
 
         const node = try Node.ErrorSetDecl.alloc(&p.arena.allocator, decls.len);
         node.* = .{
             .error_token = error_token,
             .decls_len = decls.len,
             .rbrace_token = rbrace,
         };
         std.mem.copy(*Node, node.decls(), decls);
         return &node.base;
     }
 
     /// GroupedExpr <- LPAREN Expr RPAREN
     fn parseGroupedExpr(p: *Parser) !?*Node {
         const lparen = p.eatToken(.LParen) orelse return null;
         const expr = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         const rparen = try p.expectToken(.RParen);
 
         const node = try p.arena.allocator.create(Node.GroupedExpression);
         node.* = .{
             .lparen = lparen,
             .expr = expr,
             .rparen = rparen,
         };
         return &node.base;
     }
 
     /// IfTypeExpr <- IfPrefix TypeExpr (KEYWORD_else Payload? TypeExpr)?
     fn parseIfTypeExpr(p: *Parser) !?*Node {
         return p.parseIf(parseTypeExpr);
     }
 
     /// LabeledTypeExpr
     ///     <- BlockLabel Block
     ///      / BlockLabel? LoopTypeExpr
     fn parseLabeledTypeExpr(p: *Parser) !?*Node {
         var colon: TokenIndex = undefined;
         const label = p.parseBlockLabel(&colon);
 
         if (label) |label_token| {
             if (try p.parseBlock(label_token)) |node| return node;
         }
 
         if (try p.parseLoopTypeExpr()) |node| {
             switch (node.tag) {
                 .For => node.cast(Node.For).?.label = label,
                 .While => node.cast(Node.While).?.label = label,
                 else => unreachable,
             }
             return node;
         }
 
         if (label) |token| {
             p.putBackToken(colon);
             p.putBackToken(token);
         }
         return null;
     }
 
     /// LoopTypeExpr <- KEYWORD_inline? (ForTypeExpr / WhileTypeExpr)
     fn parseLoopTypeExpr(p: *Parser) !?*Node {
         const inline_token = p.eatToken(.Keyword_inline);
 
         if (try p.parseForTypeExpr()) |node| {
             node.cast(Node.For).?.inline_token = inline_token;
             return node;
         }
 
         if (try p.parseWhileTypeExpr()) |node| {
             node.cast(Node.While).?.inline_token = inline_token;
             return node;
         }
 
         if (inline_token == null) return null;
 
         // If we've seen "inline", there should have been a "for" or "while"
         try p.errors.append(p.gpa, .{
             .ExpectedInlinable = .{ .token = p.tok_i },
         });
         return error.ParseError;
     }
 
     /// ForTypeExpr <- ForPrefix TypeExpr (KEYWORD_else TypeExpr)?
     fn parseForTypeExpr(p: *Parser) !?*Node {
         const node = (try p.parseForPrefix()) orelse return null;
         const for_prefix = node.cast(Node.For).?;
 
         const type_expr = try p.expectNode(parseTypeExpr, .{
             .ExpectedTypeExpr = .{ .token = p.tok_i },
         });
         for_prefix.body = type_expr;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const else_expr = try p.expectNode(parseTypeExpr, .{
                 .ExpectedTypeExpr = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = null,
                 .body = else_expr,
             };
 
             for_prefix.@"else" = else_node;
         }
 
         return node;
     }
 
     /// WhileTypeExpr <- WhilePrefix TypeExpr (KEYWORD_else Payload? TypeExpr)?
     fn parseWhileTypeExpr(p: *Parser) !?*Node {
         const node = (try p.parseWhilePrefix()) orelse return null;
         const while_prefix = node.cast(Node.While).?;
 
         const type_expr = try p.expectNode(parseTypeExpr, .{
             .ExpectedTypeExpr = .{ .token = p.tok_i },
         });
         while_prefix.body = type_expr;
 
         if (p.eatToken(.Keyword_else)) |else_token| {
             const payload = try p.parsePayload();
 
             const else_expr = try p.expectNode(parseTypeExpr, .{
                 .ExpectedTypeExpr = .{ .token = p.tok_i },
             });
 
             const else_node = try p.arena.allocator.create(Node.Else);
             else_node.* = .{
                 .else_token = else_token,
                 .payload = null,
                 .body = else_expr,
             };
 
             while_prefix.@"else" = else_node;
         }
 
         return node;
     }
 
     /// SwitchExpr <- KEYWORD_switch LPAREN Expr RPAREN LBRACE SwitchProngList RBRACE
     fn parseSwitchExpr(p: *Parser) !?*Node {
         const switch_token = p.eatToken(.Keyword_switch) orelse return null;
         _ = try p.expectToken(.LParen);
         const expr_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         _ = try p.expectToken(.LBrace);
         const cases = try p.parseSwitchProngList();
         defer p.gpa.free(cases);
         const rbrace = try p.expectToken(.RBrace);
 
         const node = try Node.Switch.alloc(&p.arena.allocator, cases.len);
         node.* = .{
             .switch_token = switch_token,
             .expr = expr_node,
             .cases_len = cases.len,
             .rbrace = rbrace,
         };
         std.mem.copy(*Node, node.cases(), cases);
         return &node.base;
     }
 
     /// AsmExpr <- KEYWORD_asm KEYWORD_volatile? LPAREN Expr AsmOutput? RPAREN
     /// AsmOutput <- COLON AsmOutputList AsmInput?
     /// AsmInput <- COLON AsmInputList AsmClobbers?
     /// AsmClobbers <- COLON StringList
     /// StringList <- (STRINGLITERAL COMMA)* STRINGLITERAL?
     fn parseAsmExpr(p: *Parser) !?*Node {
         const asm_token = p.eatToken(.Keyword_asm) orelse return null;
         const volatile_token = p.eatToken(.Keyword_volatile);
         _ = try p.expectToken(.LParen);
         const template = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
 
         var arena_outputs: []Node.Asm.Output = &[0]Node.Asm.Output{};
         var arena_inputs: []Node.Asm.Input = &[0]Node.Asm.Input{};
         var arena_clobbers: []*Node = &[0]*Node{};
 
         if (p.eatToken(.Colon) != null) {
             const outputs = try p.parseAsmOutputList();
             defer p.gpa.free(outputs);
             arena_outputs = try p.arena.allocator.dupe(Node.Asm.Output, outputs);
 
             if (p.eatToken(.Colon) != null) {
                 const inputs = try p.parseAsmInputList();
                 defer p.gpa.free(inputs);
                 arena_inputs = try p.arena.allocator.dupe(Node.Asm.Input, inputs);
 
                 if (p.eatToken(.Colon) != null) {
                     const clobbers = try ListParseFn(*Node, parseStringLiteral)(p);
                     defer p.gpa.free(clobbers);
                     arena_clobbers = try p.arena.allocator.dupe(*Node, clobbers);
                 }
             }
         }
 
         const node = try p.arena.allocator.create(Node.Asm);
         node.* = .{
             .asm_token = asm_token,
             .volatile_token = volatile_token,
             .template = template,
             .outputs = arena_outputs,
             .inputs = arena_inputs,
             .clobbers = arena_clobbers,
             .rparen = try p.expectToken(.RParen),
         };
 
         return &node.base;
     }
 
     /// DOT IDENTIFIER
     fn parseAnonLiteral(p: *Parser) !?*Node {
         const dot = p.eatToken(.Period) orelse return null;
 
         // anon enum literal
         if (p.eatToken(.Identifier)) |name| {
             const node = try p.arena.allocator.create(Node.EnumLiteral);
             node.* = .{
                 .dot = dot,
                 .name = name,
             };
             return &node.base;
         }
 
         if (try p.parseAnonInitList(dot)) |node| {
             return node;
         }
 
         p.putBackToken(dot);
         return null;
     }
 
     /// AsmOutputItem <- LBRACKET IDENTIFIER RBRACKET STRINGLITERAL LPAREN (MINUSRARROW TypeExpr / IDENTIFIER) RPAREN
     fn parseAsmOutputItem(p: *Parser) !?Node.Asm.Output {
         const lbracket = p.eatToken(.LBracket) orelse return null;
         const name = try p.expectNode(parseIdentifier, .{
             .ExpectedIdentifier = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RBracket);
 
         const constraint = try p.expectNode(parseStringLiteral, .{
             .ExpectedStringLiteral = .{ .token = p.tok_i },
         });
 
         _ = try p.expectToken(.LParen);
         const kind: Node.Asm.Output.Kind = blk: {
             if (p.eatToken(.Arrow) != null) {
                 const return_ident = try p.expectNode(parseTypeExpr, .{
                     .ExpectedTypeExpr = .{ .token = p.tok_i },
                 });
                 break :blk .{ .Return = return_ident };
             }
             const variable = try p.expectNode(parseIdentifier, .{
                 .ExpectedIdentifier = .{ .token = p.tok_i },
             });
             break :blk .{ .Variable = variable.castTag(.Identifier).? };
         };
         const rparen = try p.expectToken(.RParen);
 
         return Node.Asm.Output{
             .lbracket = lbracket,
             .symbolic_name = name,
             .constraint = constraint,
             .kind = kind,
             .rparen = rparen,
         };
     }
 
     /// AsmInputItem <- LBRACKET IDENTIFIER RBRACKET STRINGLITERAL LPAREN Expr RPAREN
     fn parseAsmInputItem(p: *Parser) !?Node.Asm.Input {
         const lbracket = p.eatToken(.LBracket) orelse return null;
         const name = try p.expectNode(parseIdentifier, .{
             .ExpectedIdentifier = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RBracket);
 
         const constraint = try p.expectNode(parseStringLiteral, .{
             .ExpectedStringLiteral = .{ .token = p.tok_i },
         });
 
         _ = try p.expectToken(.LParen);
         const expr = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         const rparen = try p.expectToken(.RParen);
 
         return Node.Asm.Input{
             .lbracket = lbracket,
             .symbolic_name = name,
             .constraint = constraint,
             .expr = expr,
             .rparen = rparen,
         };
     }
 
     /// BreakLabel <- COLON IDENTIFIER
     fn parseBreakLabel(p: *Parser) !?TokenIndex {
         _ = p.eatToken(.Colon) orelse return null;
         const ident = try p.expectToken(.Identifier);
         return ident;
     }
 
     /// BlockLabel <- IDENTIFIER COLON
     fn parseBlockLabel(p: *Parser, colon_token: *TokenIndex) ?TokenIndex {
         const identifier = p.eatToken(.Identifier) orelse return null;
         if (p.eatToken(.Colon)) |colon| {
             colon_token.* = colon;
             return identifier;
         }
         p.putBackToken(identifier);
         return null;
     }
 
     /// FieldInit <- DOT IDENTIFIER EQUAL Expr
     fn parseFieldInit(p: *Parser) !?*Node {
         const period_token = p.eatToken(.Period) orelse return null;
         const name_token = p.eatToken(.Identifier) orelse {
             // Because of anon literals `.{` is also valid.
             p.putBackToken(period_token);
             return null;
         };
         const eq_token = p.eatToken(.Equal) orelse {
             // `.Name` may also be an enum literal, which is a later rule.
             p.putBackToken(name_token);
             p.putBackToken(period_token);
             return null;
         };
         const expr_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
 
         const node = try p.arena.allocator.create(Node.FieldInitializer);
         node.* = .{
             .period_token = period_token,
             .name_token = name_token,
             .expr = expr_node,
         };
         return &node.base;
     }
 
     /// WhileContinueExpr <- COLON LPAREN AssignExpr RPAREN
     fn parseWhileContinueExpr(p: *Parser) !?*Node {
         _ = p.eatToken(.Colon) orelse return null;
         _ = try p.expectToken(.LParen);
         const node = try p.expectNode(parseAssignExpr, .{
             .ExpectedExprOrAssignment = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         return node;
     }
 
     /// LinkSection <- KEYWORD_linksection LPAREN Expr RPAREN
     fn parseLinkSection(p: *Parser) !?*Node {
         _ = p.eatToken(.Keyword_linksection) orelse return null;
         _ = try p.expectToken(.LParen);
         const expr_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         return expr_node;
     }
 
     /// CallConv <- KEYWORD_callconv LPAREN Expr RPAREN
     fn parseCallconv(p: *Parser) !?*Node {
         _ = p.eatToken(.Keyword_callconv) orelse return null;
         _ = try p.expectToken(.LParen);
         const expr_node = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         return expr_node;
     }
 
     /// ParamDecl <- (KEYWORD_noalias / KEYWORD_comptime)? (IDENTIFIER COLON)? ParamType
     fn parseParamDecl(p: *Parser) !?Node.FnProto.ParamDecl {
         const doc_comments = try p.parseDocComment();
         const noalias_token = p.eatToken(.Keyword_noalias);
         const comptime_token = if (noalias_token == null) p.eatToken(.Keyword_comptime) else null;
         const name_token = blk: {
             const identifier = p.eatToken(.Identifier) orelse break :blk null;
             if (p.eatToken(.Colon) != null) break :blk identifier;
             p.putBackToken(identifier); // ParamType may also be an identifier
             break :blk null;
         };
         const param_type = (try p.parseParamType()) orelse {
             // Only return cleanly if no keyword, identifier, or doc comment was found
             if (noalias_token == null and
                 comptime_token == null and
                 name_token == null and
                 doc_comments == null)
             {
                 return null;
             }
             try p.errors.append(p.gpa, .{
                 .ExpectedParamType = .{ .token = p.tok_i },
             });
             return error.ParseError;
         };
 
         return Node.FnProto.ParamDecl{
             .doc_comments = doc_comments,
             .comptime_token = comptime_token,
             .noalias_token = noalias_token,
             .name_token = name_token,
             .param_type = param_type,
         };
     }
 
     /// ParamType
     ///     <- Keyword_anytype
     ///      / DOT3
     ///      / TypeExpr
     fn parseParamType(p: *Parser) !?Node.FnProto.ParamDecl.ParamType {
         // TODO cast from tuple to error union is broken
         const P = Node.FnProto.ParamDecl.ParamType;
         if (try p.parseAnyType()) |node| return P{ .any_type = node };
         if (try p.parseTypeExpr()) |node| return P{ .type_expr = node };
         return null;
     }
 
     /// IfPrefix <- KEYWORD_if LPAREN Expr RPAREN PtrPayload?
     fn parseIfPrefix(p: *Parser) !?*Node {
         const if_token = p.eatToken(.Keyword_if) orelse return null;
         _ = try p.expectToken(.LParen);
         const condition = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         const payload = try p.parsePtrPayload();
 
         const node = try p.arena.allocator.create(Node.If);
         node.* = .{
             .if_token = if_token,
             .condition = condition,
             .payload = payload,
             .body = undefined, // set by caller
             .@"else" = null,
         };
         return &node.base;
     }
 
     /// WhilePrefix <- KEYWORD_while LPAREN Expr RPAREN PtrPayload? WhileContinueExpr?
     fn parseWhilePrefix(p: *Parser) !?*Node {
         const while_token = p.eatToken(.Keyword_while) orelse return null;
 
         _ = try p.expectToken(.LParen);
         const condition = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
 
         const payload = try p.parsePtrPayload();
         const continue_expr = try p.parseWhileContinueExpr();
 
         const node = try p.arena.allocator.create(Node.While);
         node.* = .{
             .label = null,
             .inline_token = null,
             .while_token = while_token,
             .condition = condition,
             .payload = payload,
             .continue_expr = continue_expr,
             .body = undefined, // set by caller
             .@"else" = null,
         };
         return &node.base;
     }
 
     /// ForPrefix <- KEYWORD_for LPAREN Expr RPAREN PtrIndexPayload
     fn parseForPrefix(p: *Parser) !?*Node {
         const for_token = p.eatToken(.Keyword_for) orelse return null;
 
         _ = try p.expectToken(.LParen);
         const array_expr = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
 
         const payload = try p.expectNode(parsePtrIndexPayload, .{
             .ExpectedPayload = .{ .token = p.tok_i },
         });
 
         const node = try p.arena.allocator.create(Node.For);
         node.* = .{
             .label = null,
             .inline_token = null,
             .for_token = for_token,
             .array_expr = array_expr,
             .payload = payload,
             .body = undefined, // set by caller
             .@"else" = null,
         };
         return &node.base;
     }
 
     /// Payload <- PIPE IDENTIFIER PIPE
     fn parsePayload(p: *Parser) !?*Node {
         const lpipe = p.eatToken(.Pipe) orelse return null;
         const identifier = try p.expectNode(parseIdentifier, .{
             .ExpectedIdentifier = .{ .token = p.tok_i },
         });
         const rpipe = try p.expectToken(.Pipe);
 
         const node = try p.arena.allocator.create(Node.Payload);
         node.* = .{
             .lpipe = lpipe,
             .error_symbol = identifier,
             .rpipe = rpipe,
         };
         return &node.base;
     }
 
     /// PtrPayload <- PIPE ASTERISK? IDENTIFIER PIPE
     fn parsePtrPayload(p: *Parser) !?*Node {
         const lpipe = p.eatToken(.Pipe) orelse return null;
         const asterisk = p.eatToken(.Asterisk);
         const identifier = try p.expectNode(parseIdentifier, .{
             .ExpectedIdentifier = .{ .token = p.tok_i },
         });
         const rpipe = try p.expectToken(.Pipe);
 
         const node = try p.arena.allocator.create(Node.PointerPayload);
         node.* = .{
             .lpipe = lpipe,
             .ptr_token = asterisk,
             .value_symbol = identifier,
             .rpipe = rpipe,
         };
         return &node.base;
     }
 
     /// PtrIndexPayload <- PIPE ASTERISK? IDENTIFIER (COMMA IDENTIFIER)? PIPE
     fn parsePtrIndexPayload(p: *Parser) !?*Node {
         const lpipe = p.eatToken(.Pipe) orelse return null;
         const asterisk = p.eatToken(.Asterisk);
         const identifier = try p.expectNode(parseIdentifier, .{
             .ExpectedIdentifier = .{ .token = p.tok_i },
         });
 
         const index = if (p.eatToken(.Comma) == null)
             null
         else
             try p.expectNode(parseIdentifier, .{
                 .ExpectedIdentifier = .{ .token = p.tok_i },
             });
 
         const rpipe = try p.expectToken(.Pipe);
 
         const node = try p.arena.allocator.create(Node.PointerIndexPayload);
         node.* = .{
             .lpipe = lpipe,
             .ptr_token = asterisk,
             .value_symbol = identifier,
             .index_symbol = index,
             .rpipe = rpipe,
         };
         return &node.base;
     }
 
     /// SwitchProng <- SwitchCase EQUALRARROW PtrPayload? AssignExpr
     fn parseSwitchProng(p: *Parser) !?*Node {
         const node = (try p.parseSwitchCase()) orelse return null;
         const arrow = try p.expectToken(.EqualAngleBracketRight);
         const payload = try p.parsePtrPayload();
         const expr = try p.expectNode(parseAssignExpr, .{
             .ExpectedExprOrAssignment = .{ .token = p.tok_i },
         });
 
         const switch_case = node.cast(Node.SwitchCase).?;
         switch_case.arrow_token = arrow;
         switch_case.payload = payload;
         switch_case.expr = expr;
 
         return node;
     }
 
     /// SwitchCase
     ///     <- SwitchItem (COMMA SwitchItem)* COMMA?
     ///      / KEYWORD_else
     fn parseSwitchCase(p: *Parser) !?*Node {
         var list = std.ArrayList(*Node).init(p.gpa);
         defer list.deinit();
 
         if (try p.parseSwitchItem()) |first_item| {
             try list.append(first_item);
             while (p.eatToken(.Comma) != null) {
                 const next_item = (try p.parseSwitchItem()) orelse break;
                 try list.append(next_item);
             }
         } else if (p.eatToken(.Keyword_else)) |else_token| {
             const else_node = try p.arena.allocator.create(Node.SwitchElse);
             else_node.* = .{
                 .token = else_token,
             };
             try list.append(&else_node.base);
         } else return null;
 
         const node = try Node.SwitchCase.alloc(&p.arena.allocator, list.items.len);
         node.* = .{
             .items_len = list.items.len,
             .arrow_token = undefined, // set by caller
             .payload = null,
             .expr = undefined, // set by caller
         };
         std.mem.copy(*Node, node.items(), list.items);
         return &node.base;
     }
 
     /// SwitchItem <- Expr (DOT3 Expr)?
     fn parseSwitchItem(p: *Parser) !?*Node {
         const expr = (try p.parseExpr()) orelse return null;
         if (p.eatToken(.Ellipsis3)) |token| {
             const range_end = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
 
             const node = try p.arena.allocator.create(Node.SimpleInfixOp);
             node.* = .{
                 .base = Node{ .tag = .Range },
                 .op_token = token,
                 .lhs = expr,
                 .rhs = range_end,
             };
             return &node.base;
         }
         return expr;
     }
 
     /// AssignOp
     ///     <- ASTERISKEQUAL
     ///      / SLASHEQUAL
     ///      / PERCENTEQUAL
     ///      / PLUSEQUAL
     ///      / MINUSEQUAL
     ///      / LARROW2EQUAL
     ///      / RARROW2EQUAL
     ///      / AMPERSANDEQUAL
     ///      / CARETEQUAL
     ///      / PIPEEQUAL
     ///      / ASTERISKPERCENTEQUAL
     ///      / PLUSPERCENTEQUAL
     ///      / MINUSPERCENTEQUAL
     ///      / EQUAL
     fn parseAssignOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .AsteriskEqual => .AssignMul,
             .SlashEqual => .AssignDiv,
             .PercentEqual => .AssignMod,
             .PlusEqual => .AssignAdd,
             .MinusEqual => .AssignSub,
             .AngleBracketAngleBracketLeftEqual => .AssignBitShiftLeft,
             .AngleBracketAngleBracketRightEqual => .AssignBitShiftRight,
             .AmpersandEqual => .AssignBitAnd,
             .CaretEqual => .AssignBitXor,
             .PipeEqual => .AssignBitOr,
             .AsteriskPercentEqual => .AssignMulWrap,
             .PlusPercentEqual => .AssignAddWrap,
             .MinusPercentEqual => .AssignSubWrap,
             .Equal => .Assign,
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         const node = try p.arena.allocator.create(Node.SimpleInfixOp);
         node.* = .{
             .base = .{ .tag = op },
             .op_token = token,
             .lhs = undefined, // set by caller
             .rhs = undefined, // set by caller
         };
         return &node.base;
     }
 
     /// CompareOp
     ///     <- EQUALEQUAL
     ///      / EXCLAMATIONMARKEQUAL
     ///      / LARROW
     ///      / RARROW
     ///      / LARROWEQUAL
     ///      / RARROWEQUAL
     fn parseCompareOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .EqualEqual => .EqualEqual,
             .BangEqual => .BangEqual,
             .AngleBracketLeft => .LessThan,
             .AngleBracketRight => .GreaterThan,
             .AngleBracketLeftEqual => .LessOrEqual,
             .AngleBracketRightEqual => .GreaterOrEqual,
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         return p.createInfixOp(token, op);
     }
 
     /// BitwiseOp
     ///     <- AMPERSAND
     ///      / CARET
     ///      / PIPE
     ///      / KEYWORD_orelse
     ///      / KEYWORD_catch Payload?
     fn parseBitwiseOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .Ampersand => .BitAnd,
             .Caret => .BitXor,
             .Pipe => .BitOr,
             .Keyword_orelse => .OrElse,
             .Keyword_catch => {
                 const payload = try p.parsePayload();
                 const node = try p.arena.allocator.create(Node.Catch);
                 node.* = .{
                     .op_token = token,
                     .lhs = undefined, // set by caller
                     .rhs = undefined, // set by caller
                     .payload = payload,
                 };
                 return &node.base;
             },
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         return p.createInfixOp(token, op);
     }
 
     /// BitShiftOp
     ///     <- LARROW2
     ///      / RARROW2
     fn parseBitShiftOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .AngleBracketAngleBracketLeft => .BitShiftLeft,
             .AngleBracketAngleBracketRight => .BitShiftRight,
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         return p.createInfixOp(token, op);
     }
 
     /// AdditionOp
     ///     <- PLUS
     ///      / MINUS
     ///      / PLUS2
     ///      / PLUSPERCENT
     ///      / MINUSPERCENT
     fn parseAdditionOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .Plus => .Add,
             .Minus => .Sub,
             .PlusPlus => .ArrayCat,
             .PlusPercent => .AddWrap,
             .MinusPercent => .SubWrap,
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         return p.createInfixOp(token, op);
     }
 
     /// MultiplyOp
     ///     <- PIPE2
     ///      / ASTERISK
     ///      / SLASH
     ///      / PERCENT
     ///      / ASTERISK2
     ///      / ASTERISKPERCENT
     fn parseMultiplyOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         const op: Node.Tag = switch (p.token_ids[token]) {
             .PipePipe => .MergeErrorSets,
             .Asterisk => .Mul,
             .Slash => .Div,
             .Percent => .Mod,
             .AsteriskAsterisk => .ArrayMult,
             .AsteriskPercent => .MulWrap,
             else => {
                 p.putBackToken(token);
                 return null;
             },
         };
 
         return p.createInfixOp(token, op);
     }
 
     /// PrefixOp
     ///     <- EXCLAMATIONMARK
     ///      / MINUS
     ///      / TILDE
     ///      / MINUSPERCENT
     ///      / AMPERSAND
     ///      / KEYWORD_try
     ///      / KEYWORD_await
     fn parsePrefixOp(p: *Parser) !?*Node {
         const token = p.nextToken();
         switch (p.token_ids[token]) {
             .Bang => return p.allocSimplePrefixOp(.BoolNot, token),
             .Minus => return p.allocSimplePrefixOp(.Negation, token),
             .Tilde => return p.allocSimplePrefixOp(.BitNot, token),
             .MinusPercent => return p.allocSimplePrefixOp(.NegationWrap, token),
             .Ampersand => return p.allocSimplePrefixOp(.AddressOf, token),
             .Keyword_try => return p.allocSimplePrefixOp(.Try, token),
             .Keyword_await => return p.allocSimplePrefixOp(.Await, token),
             else => {
                 p.putBackToken(token);
                 return null;
             },
         }
     }
 
     fn allocSimplePrefixOp(p: *Parser, comptime tag: Node.Tag, token: TokenIndex) !?*Node {
         const node = try p.arena.allocator.create(Node.SimplePrefixOp);
         node.* = .{
             .base = .{ .tag = tag },
             .op_token = token,
             .rhs = undefined, // set by caller
         };
         return &node.base;
     }
 
     // TODO: ArrayTypeStart is either an array or a slice, but const/allowzero only work on
     //       pointers. Consider updating this rule:
     //       ...
     //       / ArrayTypeStart
     //       / SliceTypeStart (ByteAlign / KEYWORD_const / KEYWORD_volatile / KEYWORD_allowzero)*
     //       / PtrTypeStart ...
 
     /// PrefixTypeOp
     ///     <- QUESTIONMARK
     ///      / KEYWORD_anyframe MINUSRARROW
     ///      / ArrayTypeStart (ByteAlign / KEYWORD_const / KEYWORD_volatile / KEYWORD_allowzero)*
     ///      / PtrTypeStart (KEYWORD_align LPAREN Expr (COLON INTEGER COLON INTEGER)? RPAREN / KEYWORD_const / KEYWORD_volatile / KEYWORD_allowzero)*
     fn parsePrefixTypeOp(p: *Parser) !?*Node {
         if (p.eatToken(.QuestionMark)) |token| {
             const node = try p.arena.allocator.create(Node.SimplePrefixOp);
             node.* = .{
                 .base = .{ .tag = .OptionalType },
                 .op_token = token,
                 .rhs = undefined, // set by caller
             };
             return &node.base;
         }
 
         if (p.eatToken(.Keyword_anyframe)) |token| {
             const arrow = p.eatToken(.Arrow) orelse {
                 p.putBackToken(token);
                 return null;
             };
             const node = try p.arena.allocator.create(Node.AnyFrameType);
             node.* = .{
                 .anyframe_token = token,
                 .result = .{
                     .arrow_token = arrow,
                     .return_type = undefined, // set by caller
                 },
             };
             return &node.base;
         }
 
         if (try p.parsePtrTypeStart()) |node| {
             // If the token encountered was **, there will be two nodes instead of one.
             // The attributes should be applied to the rightmost operator.
             var ptr_info = if (node.cast(Node.PtrType)) |ptr_type|
                 if (p.token_ids[ptr_type.op_token] == .AsteriskAsterisk)
                     &ptr_type.rhs.cast(Node.PtrType).?.ptr_info
                 else
                     &ptr_type.ptr_info
             else if (node.cast(Node.SliceType)) |slice_type|
                 &slice_type.ptr_info
             else
                 unreachable;
 
             while (true) {
                 if (p.eatToken(.Keyword_align)) |align_token| {
                     const lparen = try p.expectToken(.LParen);
                     const expr_node = try p.expectNode(parseExpr, .{
                         .ExpectedExpr = .{ .token = p.tok_i },
                     });
 
                     // Optional bit range
                     const bit_range = if (p.eatToken(.Colon)) |_| bit_range_value: {
                         const range_start = try p.expectNode(parseIntegerLiteral, .{
                             .ExpectedIntegerLiteral = .{ .token = p.tok_i },
                         });
                         _ = try p.expectToken(.Colon);
                         const range_end = try p.expectNode(parseIntegerLiteral, .{
                             .ExpectedIntegerLiteral = .{ .token = p.tok_i },
                         });
 
                         break :bit_range_value ast.PtrInfo.Align.BitRange{
                             .start = range_start,
                             .end = range_end,
                         };
                     } else null;
                     _ = try p.expectToken(.RParen);
 
                     if (ptr_info.align_info != null) {
                         try p.errors.append(p.gpa, .{
                             .ExtraAlignQualifier = .{ .token = p.tok_i - 1 },
                         });
                         continue;
                     }
 
                     ptr_info.align_info = ast.PtrInfo.Align{
                         .node = expr_node,
                         .bit_range = bit_range,
                     };
 
                     continue;
                 }
                 if (p.eatToken(.Keyword_const)) |const_token| {
                     if (ptr_info.const_token != null) {
                         try p.errors.append(p.gpa, .{
                             .ExtraConstQualifier = .{ .token = p.tok_i - 1 },
                         });
                         continue;
                     }
                     ptr_info.const_token = const_token;
                     continue;
                 }
                 if (p.eatToken(.Keyword_volatile)) |volatile_token| {
                     if (ptr_info.volatile_token != null) {
                         try p.errors.append(p.gpa, .{
                             .ExtraVolatileQualifier = .{ .token = p.tok_i - 1 },
                         });
                         continue;
                     }
                     ptr_info.volatile_token = volatile_token;
                     continue;
                 }
                 if (p.eatToken(.Keyword_allowzero)) |allowzero_token| {
                     if (ptr_info.allowzero_token != null) {
                         try p.errors.append(p.gpa, .{
                             .ExtraAllowZeroQualifier = .{ .token = p.tok_i - 1 },
                         });
                         continue;
                     }
                     ptr_info.allowzero_token = allowzero_token;
                     continue;
                 }
                 break;
             }
 
             return node;
         }
 
         if (try p.parseArrayTypeStart()) |node| {
             if (node.cast(Node.SliceType)) |slice_type| {
                 // Collect pointer qualifiers in any order, but disallow duplicates
                 while (true) {
                     if (try p.parseByteAlign()) |align_expr| {
                         if (slice_type.ptr_info.align_info != null) {
                             try p.errors.append(p.gpa, .{
                                 .ExtraAlignQualifier = .{ .token = p.tok_i - 1 },
                             });
                             continue;
                         }
                         slice_type.ptr_info.align_info = ast.PtrInfo.Align{
                             .node = align_expr,
                             .bit_range = null,
                         };
                         continue;
                     }
                     if (p.eatToken(.Keyword_const)) |const_token| {
                         if (slice_type.ptr_info.const_token != null) {
                             try p.errors.append(p.gpa, .{
                                 .ExtraConstQualifier = .{ .token = p.tok_i - 1 },
                             });
                             continue;
                         }
                         slice_type.ptr_info.const_token = const_token;
                         continue;
                     }
                     if (p.eatToken(.Keyword_volatile)) |volatile_token| {
                         if (slice_type.ptr_info.volatile_token != null) {
                             try p.errors.append(p.gpa, .{
                                 .ExtraVolatileQualifier = .{ .token = p.tok_i - 1 },
                             });
                             continue;
                         }
                         slice_type.ptr_info.volatile_token = volatile_token;
                         continue;
                     }
                     if (p.eatToken(.Keyword_allowzero)) |allowzero_token| {
                         if (slice_type.ptr_info.allowzero_token != null) {
                             try p.errors.append(p.gpa, .{
                                 .ExtraAllowZeroQualifier = .{ .token = p.tok_i - 1 },
                             });
                             continue;
                         }
                         slice_type.ptr_info.allowzero_token = allowzero_token;
                         continue;
                     }
                     break;
                 }
             }
             return node;
         }
 
         return null;
     }
 
     /// SuffixOp
     ///     <- LBRACKET Expr (DOT2 (Expr (COLON Expr)?)?)? RBRACKET
     ///      / DOT IDENTIFIER
     ///      / DOTASTERISK
     ///      / DOTQUESTIONMARK
     fn parseSuffixOp(p: *Parser, lhs: *Node) !?*Node {
         if (p.eatToken(.LBracket)) |_| {
             const index_expr = try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             });
 
             if (p.eatToken(.Ellipsis2) != null) {
                 const end_expr = try p.parseExpr();
                 const sentinel: ?*Node = if (p.eatToken(.Colon) != null)
                     try p.parseExpr()
                 else
                     null;
                 const rtoken = try p.expectToken(.RBracket);
                 const node = try p.arena.allocator.create(Node.Slice);
                 node.* = .{
                     .lhs = lhs,
                     .rtoken = rtoken,
                     .start = index_expr,
                     .end = end_expr,
                     .sentinel = sentinel,
                 };
                 return &node.base;
             }
 
             const rtoken = try p.expectToken(.RBracket);
             const node = try p.arena.allocator.create(Node.ArrayAccess);
             node.* = .{
                 .lhs = lhs,
                 .rtoken = rtoken,
                 .index_expr = index_expr,
             };
             return &node.base;
         }
 
         if (p.eatToken(.PeriodAsterisk)) |period_asterisk| {
             const node = try p.arena.allocator.create(Node.SimpleSuffixOp);
             node.* = .{
                 .base = .{ .tag = .Deref },
                 .lhs = lhs,
                 .rtoken = period_asterisk,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Invalid_periodasterisks)) |period_asterisk| {
             try p.errors.append(p.gpa, .{
                 .AsteriskAfterPointerDereference = .{ .token = period_asterisk },
             });
             const node = try p.arena.allocator.create(Node.SimpleSuffixOp);
             node.* = .{
                 .base = .{ .tag = .Deref },
                 .lhs = lhs,
                 .rtoken = period_asterisk,
             };
             return &node.base;
         }
 
         if (p.eatToken(.Period)) |period| {
             if (try p.parseIdentifier()) |identifier| {
                 const node = try p.arena.allocator.create(Node.SimpleInfixOp);
                 node.* = .{
                     .base = Node{ .tag = .Period },
                     .op_token = period,
                     .lhs = lhs,
                     .rhs = identifier,
                 };
                 return &node.base;
             }
             if (p.eatToken(.QuestionMark)) |question_mark| {
                 const node = try p.arena.allocator.create(Node.SimpleSuffixOp);
                 node.* = .{
                     .base = .{ .tag = .UnwrapOptional },
                     .lhs = lhs,
                     .rtoken = question_mark,
                 };
                 return &node.base;
             }
             try p.errors.append(p.gpa, .{
                 .ExpectedSuffixOp = .{ .token = p.tok_i },
             });
             return null;
         }
 
         return null;
     }
 
     /// FnCallArguments <- LPAREN ExprList RPAREN
     /// ExprList <- (Expr COMMA)* Expr?
     fn parseFnCallArguments(p: *Parser) !?AnnotatedParamList {
         if (p.eatToken(.LParen) == null) return null;
         const list = try ListParseFn(*Node, parseExpr)(p);
         errdefer p.gpa.free(list);
         const rparen = try p.expectToken(.RParen);
         return AnnotatedParamList{ .list = list, .rparen = rparen };
     }
 
     const AnnotatedParamList = struct {
         list: []*Node,
         rparen: TokenIndex,
     };
 
     /// ArrayTypeStart <- LBRACKET Expr? RBRACKET
     fn parseArrayTypeStart(p: *Parser) !?*Node {
         const lbracket = p.eatToken(.LBracket) orelse return null;
         const expr = try p.parseExpr();
         const sentinel = if (p.eatToken(.Colon)) |_|
             try p.expectNode(parseExpr, .{
                 .ExpectedExpr = .{ .token = p.tok_i },
             })
         else
             null;
         const rbracket = try p.expectToken(.RBracket);
 
         if (expr) |len_expr| {
             if (sentinel) |s| {
                 const node = try p.arena.allocator.create(Node.ArrayTypeSentinel);
                 node.* = .{
                     .op_token = lbracket,
                     .rhs = undefined, // set by caller
                     .len_expr = len_expr,
                     .sentinel = s,
                 };
                 return &node.base;
             } else {
                 const node = try p.arena.allocator.create(Node.ArrayType);
                 node.* = .{
                     .op_token = lbracket,
                     .rhs = undefined, // set by caller
                     .len_expr = len_expr,
                 };
                 return &node.base;
             }
         }
 
         const node = try p.arena.allocator.create(Node.SliceType);
         node.* = .{
             .op_token = lbracket,
             .rhs = undefined, // set by caller
             .ptr_info = .{ .sentinel = sentinel },
         };
         return &node.base;
     }
 
     /// PtrTypeStart
     ///     <- ASTERISK
     ///      / ASTERISK2
     ///      / PTRUNKNOWN
     ///      / PTRC
     fn parsePtrTypeStart(p: *Parser) !?*Node {
         if (p.eatToken(.Asterisk)) |asterisk| {
             const sentinel = if (p.eatToken(.Colon)) |_|
                 try p.expectNode(parseExpr, .{
                     .ExpectedExpr = .{ .token = p.tok_i },
                 })
             else
                 null;
             const node = try p.arena.allocator.create(Node.PtrType);
             node.* = .{
                 .op_token = asterisk,
                 .rhs = undefined, // set by caller
                 .ptr_info = .{ .sentinel = sentinel },
             };
             return &node.base;
         }
 
         if (p.eatToken(.AsteriskAsterisk)) |double_asterisk| {
             const node = try p.arena.allocator.create(Node.PtrType);
             node.* = .{
                 .op_token = double_asterisk,
                 .rhs = undefined, // set by caller
             };
 
             // Special case for **, which is its own token
             const child = try p.arena.allocator.create(Node.PtrType);
             child.* = .{
                 .op_token = double_asterisk,
                 .rhs = undefined, // set by caller
             };
             node.rhs = &child.base;
 
             return &node.base;
         }
         if (p.eatToken(.LBracket)) |lbracket| {
             const asterisk = p.eatToken(.Asterisk) orelse {
                 p.putBackToken(lbracket);
                 return null;
             };
             if (p.eatToken(.Identifier)) |ident| {
                 const token_loc = p.token_locs[ident];
                 const token_slice = p.source[token_loc.start..token_loc.end];
                 if (!std.mem.eql(u8, token_slice, "c")) {
                     p.putBackToken(ident);
                 } else {
                     _ = try p.expectToken(.RBracket);
                     const node = try p.arena.allocator.create(Node.PtrType);
                     node.* = .{
                         .op_token = lbracket,
                         .rhs = undefined, // set by caller
                     };
                     return &node.base;
                 }
             }
             const sentinel = if (p.eatToken(.Colon)) |_|
                 try p.expectNode(parseExpr, .{
                     .ExpectedExpr = .{ .token = p.tok_i },
                 })
             else
                 null;
             _ = try p.expectToken(.RBracket);
             const node = try p.arena.allocator.create(Node.PtrType);
             node.* = .{
                 .op_token = lbracket,
                 .rhs = undefined, // set by caller
                 .ptr_info = .{ .sentinel = sentinel },
             };
             return &node.base;
         }
         return null;
     }
 
     /// ContainerDeclAuto <- ContainerDeclType LBRACE ContainerMembers RBRACE
     fn parseContainerDeclAuto(p: *Parser) !?*Node {
         const container_decl_type = (try p.parseContainerDeclType()) orelse return null;
         const lbrace = try p.expectToken(.LBrace);
         const members = try p.parseContainerMembers(false);
         defer p.gpa.free(members);
         const rbrace = try p.expectToken(.RBrace);
 
         const members_len = @intCast(NodeIndex, members.len);
         const node = try Node.ContainerDecl.alloc(&p.arena.allocator, members_len);
         node.* = .{
             .layout_token = null,
             .kind_token = container_decl_type.kind_token,
             .init_arg_expr = container_decl_type.init_arg_expr,
             .fields_and_decls_len = members_len,
             .lbrace_token = lbrace,
             .rbrace_token = rbrace,
         };
         std.mem.copy(*Node, node.fieldsAndDecls(), members);
         return &node.base;
     }
 
     /// Holds temporary data until we are ready to construct the full ContainerDecl AST node.
     const ContainerDeclType = struct {
         kind_token: TokenIndex,
         init_arg_expr: Node.ContainerDecl.InitArg,
     };
 
     /// ContainerDeclType
     ///     <- KEYWORD_struct
     ///      / KEYWORD_enum (LPAREN Expr RPAREN)?
     ///      / KEYWORD_union (LPAREN (KEYWORD_enum (LPAREN Expr RPAREN)? / Expr) RPAREN)?
     ///      / KEYWORD_opaque
     fn parseContainerDeclType(p: *Parser) !?ContainerDeclType {
         const kind_token = p.nextToken();
 
         const init_arg_expr = switch (p.token_ids[kind_token]) {
             .Keyword_struct, .Keyword_opaque => Node.ContainerDecl.InitArg{ .None = {} },
             .Keyword_enum => blk: {
                 if (p.eatToken(.LParen) != null) {
                     const expr = try p.expectNode(parseExpr, .{
                         .ExpectedExpr = .{ .token = p.tok_i },
                     });
                     _ = try p.expectToken(.RParen);
                     break :blk Node.ContainerDecl.InitArg{ .Type = expr };
                 }
                 break :blk Node.ContainerDecl.InitArg{ .None = {} };
             },
             .Keyword_union => blk: {
                 if (p.eatToken(.LParen) != null) {
                     if (p.eatToken(.Keyword_enum) != null) {
                         if (p.eatToken(.LParen) != null) {
                             const expr = try p.expectNode(parseExpr, .{
                                 .ExpectedExpr = .{ .token = p.tok_i },
                             });
                             _ = try p.expectToken(.RParen);
                             _ = try p.expectToken(.RParen);
                             break :blk Node.ContainerDecl.InitArg{ .Enum = expr };
                         }
                         _ = try p.expectToken(.RParen);
                         break :blk Node.ContainerDecl.InitArg{ .Enum = null };
                     }
                     const expr = try p.expectNode(parseExpr, .{
                         .ExpectedExpr = .{ .token = p.tok_i },
                     });
                     _ = try p.expectToken(.RParen);
                     break :blk Node.ContainerDecl.InitArg{ .Type = expr };
                 }
                 break :blk Node.ContainerDecl.InitArg{ .None = {} };
             },
             else => {
                 p.putBackToken(kind_token);
                 return null;
             },
         };
 
         return ContainerDeclType{
             .kind_token = kind_token,
             .init_arg_expr = init_arg_expr,
         };
     }
 
     /// ByteAlign <- KEYWORD_align LPAREN Expr RPAREN
     fn parseByteAlign(p: *Parser) !?*Node {
         _ = p.eatToken(.Keyword_align) orelse return null;
         _ = try p.expectToken(.LParen);
         const expr = try p.expectNode(parseExpr, .{
             .ExpectedExpr = .{ .token = p.tok_i },
         });
         _ = try p.expectToken(.RParen);
         return expr;
     }
 
     /// IdentifierList <- (IDENTIFIER COMMA)* IDENTIFIER?
     /// Only ErrorSetDecl parses an IdentifierList
     fn parseErrorTagList(p: *Parser) ![]*Node {
         return ListParseFn(*Node, parseErrorTag)(p);
     }
 
     /// SwitchProngList <- (SwitchProng COMMA)* SwitchProng?
     fn parseSwitchProngList(p: *Parser) ![]*Node {
         return ListParseFn(*Node, parseSwitchProng)(p);
     }
 
     /// AsmOutputList <- (AsmOutputItem COMMA)* AsmOutputItem?
     fn parseAsmOutputList(p: *Parser) Error![]Node.Asm.Output {
         return ListParseFn(Node.Asm.Output, parseAsmOutputItem)(p);
     }
 
     /// AsmInputList <- (AsmInputItem COMMA)* AsmInputItem?
     fn parseAsmInputList(p: *Parser) Error![]Node.Asm.Input {
         return ListParseFn(Node.Asm.Input, parseAsmInputItem)(p);
     }
 
     /// ParamDeclList <- (ParamDecl COMMA)* ParamDecl?
     fn parseParamDeclList(p: *Parser) ![]Node.FnProto.ParamDecl {
         return ListParseFn(Node.FnProto.ParamDecl, parseParamDecl)(p);
     }
 
     const NodeParseFn = fn (p: *Parser) Error!?*Node;
 
     fn ListParseFn(comptime E: type, comptime nodeParseFn: anytype) ParseFn([]E) {
         return struct {
             pub fn parse(p: *Parser) ![]E {
                 var list = std.ArrayList(E).init(p.gpa);
                 defer list.deinit();
 
                 while (try nodeParseFn(p)) |item| {
                     try list.append(item);
 
                     switch (p.token_ids[p.tok_i]) {
                         .Comma => _ = p.nextToken(),
                         // all possible delimiters
                         .Colon, .RParen, .RBrace, .RBracket => break,
                         else => {
                             // this is likely just a missing comma,
                             // continue parsing this list and give an error
                             try p.errors.append(p.gpa, .{
                                 .ExpectedToken = .{ .token = p.tok_i, .expected_id = .Comma },
                             });
                         },
                     }
                 }
                 return list.toOwnedSlice();
             }
         }.parse;
     }
 
     fn SimpleBinOpParseFn(comptime token: Token.Id, comptime op: Node.Tag) NodeParseFn {
         return struct {
             pub fn parse(p: *Parser) Error!?*Node {
                 const op_token = if (token == .Keyword_and) switch (p.token_ids[p.tok_i]) {
                     .Keyword_and => p.nextToken(),
                     .Invalid_ampersands => blk: {
                         try p.errors.append(p.gpa, .{
                             .InvalidAnd = .{ .token = p.tok_i },
                         });
                         break :blk p.nextToken();
                     },
                     else => return null,
                 } else p.eatToken(token) orelse return null;
 
                 const node = try p.arena.allocator.create(Node.SimpleInfixOp);
                 node.* = .{
                     .base = .{ .tag = op },
                     .op_token = op_token,
                     .lhs = undefined, // set by caller
                     .rhs = undefined, // set by caller
                 };
                 return &node.base;
             }
         }.parse;
     }
 
     // Helper parsers not included in the grammar
 
     fn parseBuiltinCall(p: *Parser) !?*Node {
         const token = p.eatToken(.Builtin) orelse return null;
         const params = (try p.parseFnCallArguments()) orelse {
             try p.errors.append(p.gpa, .{
                 .ExpectedParamList = .{ .token = p.tok_i },
             });
 
             // lets pretend this was an identifier so we can continue parsing
             const node = try p.arena.allocator.create(Node.OneToken);
             node.* = .{
                 .base = .{ .tag = .Identifier },
                 .token = token,
             };
             return &node.base;
         };
         defer p.gpa.free(params.list);
 
         const node = try Node.BuiltinCall.alloc(&p.arena.allocator, params.list.len);
         node.* = .{
             .builtin_token = token,
             .params_len = params.list.len,
             .rparen_token = params.rparen,
         };
         std.mem.copy(*Node, node.params(), params.list);
         return &node.base;
     }
 
     fn parseErrorTag(p: *Parser) !?*Node {
         const doc_comments = try p.parseDocComment(); // no need to rewind on failure
         const token = p.eatToken(.Identifier) orelse return null;
 
         const node = try p.arena.allocator.create(Node.ErrorTag);
         node.* = .{
             .doc_comments = doc_comments,
             .name_token = token,
         };
         return &node.base;
     }
 
     fn parseIdentifier(p: *Parser) !?*Node {
         const token = p.eatToken(.Identifier) orelse return null;
         const node = try p.arena.allocator.create(Node.OneToken);
         node.* = .{
             .base = .{ .tag = .Identifier },
             .token = token,
         };
         return &node.base;
     }
 
     fn parseAnyType(p: *Parser) !?*Node {
         const token = p.eatToken(.Keyword_anytype) orelse
             p.eatToken(.Keyword_var) orelse return null; // TODO remove in next release cycle
         const node = try p.arena.allocator.create(Node.OneToken);
         node.* = .{
             .base = .{ .tag = .AnyType },
             .token = token,
         };
         return &node.base;
     }
 
     fn createLiteral(p: *Parser, tag: ast.Node.Tag, token: TokenIndex) !*Node {
         const result = try p.arena.allocator.create(Node.OneToken);
         result.* = .{
             .base = .{ .tag = tag },
             .token = token,
         };
         return &result.base;
     }
 
     fn parseStringLiteralSingle(p: *Parser) !?*Node {
         if (p.eatToken(.StringLiteral)) |token| {
             const node = try p.arena.allocator.create(Node.OneToken);
             node.* = .{
                 .base = .{ .tag = .StringLiteral },
                 .token = token,
             };
             return &node.base;
         }
         return null;
     }
 
     // string literal or multiline string literal
     fn parseStringLiteral(p: *Parser) !?*Node {
         if (try p.parseStringLiteralSingle()) |node| return node;
 
         if (p.eatToken(.MultilineStringLiteralLine)) |first_line| {
             const start_tok_i = p.tok_i;
             var tok_i = start_tok_i;
             var count: usize = 1; // including first_line
             while (true) : (tok_i += 1) {
                 switch (p.token_ids[tok_i]) {
                     .LineComment => continue,
                     .MultilineStringLiteralLine => count += 1,
                     else => break,
                 }
             }
 
             const node = try Node.MultilineStringLiteral.alloc(&p.arena.allocator, count);
             node.* = .{ .lines_len = count };
             const lines = node.lines();
             tok_i = start_tok_i;
             lines[0] = first_line;
             count = 1;
             while (true) : (tok_i += 1) {
                 switch (p.token_ids[tok_i]) {
                     .LineComment => continue,
                     .MultilineStringLiteralLine => {
                         lines[count] = tok_i;
                         count += 1;
                     },
                     else => break,
                 }
             }
             p.tok_i = tok_i;
             return &node.base;
         }
 
         return null;
     }
 
     fn parseIntegerLiteral(p: *Parser) !?*Node {
         const token = p.eatToken(.IntegerLiteral) orelse return null;
         const node = try p.arena.allocator.create(Node.OneToken);
         node.* = .{
             .base = .{ .tag = .IntegerLiteral },
             .token = token,
         };
         return &node.base;
     }
 
     fn parseFloatLiteral(p: *Parser) !?*Node {
         const token = p.eatToken(.FloatLiteral) orelse return null;
         const node = try p.arena.allocator.create(Node.OneToken);
         node.* = .{
             .base = .{ .tag = .FloatLiteral },
             .token = token,
         };
         return &node.base;
     }
 
     fn parseTry(p: *Parser) !?*Node {
         const token = p.eatToken(.Keyword_try) orelse return null;
         const node = try p.arena.allocator.create(Node.SimplePrefixOp);
         node.* = .{
             .base = .{ .tag = .Try },
             .op_token = token,
             .rhs = undefined, // set by caller
         };
         return &node.base;
     }
 
     /// IfPrefix Body (KEYWORD_else Payload? Body)?
     fn parseIf(p: *Parser, bodyParseFn: NodeParseFn) !?*Node {
         const node = (try p.parseIfPrefix()) orelse return null;
         const if_prefix = node.cast(Node.If).?;
 
         if_prefix.body = try p.expectNode(bodyParseFn, .{
             .InvalidToken = .{ .token = p.tok_i },
         });
 
         const else_token = p.eatToken(.Keyword_else) orelse return node;
         const payload = try p.parsePayload();
         const else_expr = try p.expectNode(bodyParseFn, .{
             .InvalidToken = .{ .token = p.tok_i },
         });
         const else_node = try p.arena.allocator.create(Node.Else);
         else_node.* = .{
             .else_token = else_token,
             .payload = payload,
             .body = else_expr,
         };
         if_prefix.@"else" = else_node;
 
         return node;
     }
 
     /// Eat a multiline doc comment
     fn parseDocComment(p: *Parser) !?*Node.DocComment {
         if (p.eatToken(.DocComment)) |first_line| {
             while (p.eatToken(.DocComment)) |_| {}
             const node = try p.arena.allocator.create(Node.DocComment);
             node.* = .{ .first_line = first_line };
             return node;
         }
         return null;
     }
 
     fn tokensOnSameLine(p: *Parser, token1: TokenIndex, token2: TokenIndex) bool {
         return std.mem.indexOfScalar(u8, p.source[p.token_locs[token1].end..p.token_locs[token2].start], '\n') == null;
     }
 
     /// Eat a single-line doc comment on the same line as another node
     fn parseAppendedDocComment(p: *Parser, after_token: TokenIndex) !?*Node.DocComment {
         const comment_token = p.eatToken(.DocComment) orelse return null;
         if (p.tokensOnSameLine(after_token, comment_token)) {
             const node = try p.arena.allocator.create(Node.DocComment);
             node.* = .{ .first_line = comment_token };
             return node;
         }
         p.putBackToken(comment_token);
         return null;
     }
 
     /// Op* Child
     fn parsePrefixOpExpr(p: *Parser, comptime opParseFn: NodeParseFn, comptime childParseFn: NodeParseFn) Error!?*Node {
         if (try opParseFn(p)) |first_op| {
             var rightmost_op = first_op;
             while (true) {
                 switch (rightmost_op.tag) {
                     .AddressOf,
                     .Await,
                     .BitNot,
                     .BoolNot,
                     .OptionalType,
                     .Negation,
                     .NegationWrap,
                     .Resume,
                     .Try,
                     => {
                         if (try opParseFn(p)) |rhs| {
                             rightmost_op.cast(Node.SimplePrefixOp).?.rhs = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     .ArrayType => {
                         if (try opParseFn(p)) |rhs| {
                             rightmost_op.cast(Node.ArrayType).?.rhs = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     .ArrayTypeSentinel => {
                         if (try opParseFn(p)) |rhs| {
                             rightmost_op.cast(Node.ArrayTypeSentinel).?.rhs = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     .SliceType => {
                         if (try opParseFn(p)) |rhs| {
                             rightmost_op.cast(Node.SliceType).?.rhs = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     .PtrType => {
                         var ptr_type = rightmost_op.cast(Node.PtrType).?;
                         // If the token encountered was **, there will be two nodes
                         if (p.token_ids[ptr_type.op_token] == .AsteriskAsterisk) {
                             rightmost_op = ptr_type.rhs;
                             ptr_type = rightmost_op.cast(Node.PtrType).?;
                         }
                         if (try opParseFn(p)) |rhs| {
                             ptr_type.rhs = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     .AnyFrameType => {
                         const prom = rightmost_op.cast(Node.AnyFrameType).?;
                         if (try opParseFn(p)) |rhs| {
                             prom.result.?.return_type = rhs;
                             rightmost_op = rhs;
                         } else break;
                     },
                     else => unreachable,
                 }
             }
 
             // If any prefix op existed, a child node on the RHS is required
             switch (rightmost_op.tag) {
                 .AddressOf,
                 .Await,
                 .BitNot,
                 .BoolNot,
                 .OptionalType,
                 .Negation,
                 .NegationWrap,
                 .Resume,
                 .Try,
                 => {
                     const prefix_op = rightmost_op.cast(Node.SimplePrefixOp).?;
                     prefix_op.rhs = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 .ArrayType => {
                     const prefix_op = rightmost_op.cast(Node.ArrayType).?;
                     prefix_op.rhs = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 .ArrayTypeSentinel => {
                     const prefix_op = rightmost_op.cast(Node.ArrayTypeSentinel).?;
                     prefix_op.rhs = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 .PtrType => {
                     const prefix_op = rightmost_op.cast(Node.PtrType).?;
                     prefix_op.rhs = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 .SliceType => {
                     const prefix_op = rightmost_op.cast(Node.SliceType).?;
                     prefix_op.rhs = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 .AnyFrameType => {
                     const prom = rightmost_op.cast(Node.AnyFrameType).?;
                     prom.result.?.return_type = try p.expectNode(childParseFn, .{
                         .InvalidToken = .{ .token = p.tok_i },
                     });
                 },
                 else => unreachable,
             }
 
             return first_op;
         }
 
         // Otherwise, the child node is optional
         return childParseFn(p);
     }
 
     /// Child (Op Child)*
     /// Child (Op Child)?
     fn parseBinOpExpr(
         p: *Parser,
         opParseFn: NodeParseFn,
         childParseFn: NodeParseFn,
         chain: enum {
             Once,
             Infinitely,
         },
     ) Error!?*Node {
         var res = (try childParseFn(p)) orelse return null;
 
         while (try opParseFn(p)) |node| {
             const right = try p.expectNode(childParseFn, .{
                 .InvalidToken = .{ .token = p.tok_i },
             });
             const left = res;
             res = node;
 
             if (node.castTag(.Catch)) |op| {
                 op.lhs = left;
                 op.rhs = right;
             } else if (node.cast(Node.SimpleInfixOp)) |op| {
                 op.lhs = left;
                 op.rhs = right;
             }
 
             switch (chain) {
                 .Once => break,
                 .Infinitely => continue,
             }
         }
 
         return res;
     }
 
     fn createInfixOp(p: *Parser, op_token: TokenIndex, tag: Node.Tag) !*Node {
         const node = try p.arena.allocator.create(Node.SimpleInfixOp);
         node.* = .{
             .base = Node{ .tag = tag },
             .op_token = op_token,
             .lhs = undefined, // set by caller
             .rhs = undefined, // set by caller
         };
         return &node.base;
     }
 
     fn eatToken(p: *Parser, id: Token.Id) ?TokenIndex {
         return if (p.token_ids[p.tok_i] == id) p.nextToken() else null;
     }
 
     fn expectToken(p: *Parser, id: Token.Id) Error!TokenIndex {
         return (try p.expectTokenRecoverable(id)) orelse error.ParseError;
     }
 
     fn expectTokenRecoverable(p: *Parser, id: Token.Id) !?TokenIndex {
         const token = p.nextToken();
         if (p.token_ids[token] != id) {
             try p.errors.append(p.gpa, .{
                 .ExpectedToken = .{ .token = token, .expected_id = id },
             });
             // go back so that we can recover properly
             p.putBackToken(token);
             return null;
         }
         return token;
     }
 
     fn nextToken(p: *Parser) TokenIndex {
         const result = p.tok_i;
         p.tok_i += 1;
         assert(p.token_ids[result] != .LineComment);
         if (p.tok_i >= p.token_ids.len) return result;
 
         while (true) {
             if (p.token_ids[p.tok_i] != .LineComment) return result;
             p.tok_i += 1;
         }
     }
 
     fn putBackToken(p: *Parser, putting_back: TokenIndex) void {
         while (p.tok_i > 0) {
             p.tok_i -= 1;
             if (p.token_ids[p.tok_i] == .LineComment) continue;
             assert(putting_back == p.tok_i);
             return;
         }
     }
 
     /// TODO Delete this function. I don't like the inversion of control.
     fn expectNode(
         p: *Parser,
         parseFn: NodeParseFn,
         /// if parsing fails
         err: AstError,
     ) Error!*Node {
         return (try p.expectNodeRecoverable(parseFn, err)) orelse return error.ParseError;
     }
 
     /// TODO Delete this function. I don't like the inversion of control.
     fn expectNodeRecoverable(
         p: *Parser,
         parseFn: NodeParseFn,
         /// if parsing fails
         err: AstError,
     ) !?*Node {
         return (try parseFn(p)) orelse {
             try p.errors.append(p.gpa, err);
             return null;
         };
     }
 };
 
 fn ParseFn(comptime T: type) type {
     return fn (p: *Parser) Error!T;
 }
 
 test "std.zig.parser" {
     _ = @import("parser_test.zig");
 }