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Add support for both '_' and 'else' prongs at the same time in switch statements

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If both are used, 'else' handles named members and '_' handles
unnamed members. In this case the 'else' prong will be unrolled
to an explicit case containing all remaining named values.
This commit is contained in:
Justus Klausecker
2025-07-10 01:58:02 +02:00
parent 1d9b1c0212
commit ba549a7d67
11 changed files with 770 additions and 364 deletions
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18
lib/std/zig/Ast.zig
View File

@@ -2877,24 +2877,6 @@ pub const full = struct {
arrow_token: TokenIndex,
target_expr: Node.Index,
};
/// Returns:
/// `null` if case is not special
/// `.none` if case is else prong
/// Index of underscore otherwise
pub fn isSpecial(case: *const SwitchCase, tree: *const Ast) ?Node.OptionalIndex {
if (case.ast.values.len == 0) {
return .none;
}
for (case.ast.values) |val| {
if (tree.nodeTag(val) == .identifier and
mem.eql(u8, tree.tokenSlice(tree.nodeMainToken(val)), "_"))
{
return val.toOptional();
}
}
return null;
}
};
pub const Asm = struct {

149
lib/std/zig/AstGen.zig
View File

@@ -7662,11 +7662,12 @@ fn switchExpr(
var scalar_cases_len: u32 = 0;
var multi_cases_len: u32 = 0;
var inline_cases_len: u32 = 0;
var special_prong: Zir.SpecialProng = .none;
var special_node: Ast.Node.OptionalIndex = .none;
var else_case_node: Ast.Node.OptionalIndex = .none;
var else_src: ?Ast.TokenIndex = null;
var underscore_src: ?Ast.TokenIndex = null;
var underscore_case_node: Ast.Node.OptionalIndex = .none;
var underscore_node: Ast.Node.OptionalIndex = .none;
var underscore_src: ?Ast.TokenIndex = null;
var underscore_additional_items: Zir.SpecialProngs.AdditionalItems = .none;
for (case_nodes) |case_node| {
const case = tree.fullSwitchCase(case_node).?;
if (case.payload_token) |payload_token| {
@@ -7687,6 +7688,7 @@ fn switchExpr(
any_non_inline_capture = true;
}
}
// Check for else prong.
if (case.ast.values.len == 0) {
const case_src = case.ast.arrow_token - 1;
@@ -7703,40 +7705,21 @@ fn switchExpr(
),
},
);
} else if (underscore_src) |some_underscore| {
return astgen.failNodeNotes(
node,
"else and '_' prong in switch expression",
.{},
&[_]u32{
try astgen.errNoteTok(
case_src,
"else prong here",
.{},
),
try astgen.errNoteTok(
some_underscore,
"'_' prong here",
.{},
),
},
);
}
special_node = case_node.toOptional();
special_prong = .@"else";
else_case_node = case_node.toOptional();
else_src = case_src;
continue;
}
// Check for '_' prong.
var found_underscore = false;
var case_has_underscore = false;
for (case.ast.values) |val| {
switch (tree.nodeTag(val)) {
.identifier => if (mem.eql(u8, tree.tokenSlice(tree.nodeMainToken(val)), "_")) {
const case_src = case.ast.arrow_token - 1;
const val_src = tree.nodeMainToken(val);
if (underscore_src) |src| {
return astgen.failTokNotes(
case_src,
val_src,
"multiple '_' prongs in switch expression",
.{},
&[_]u32{
@@ -7747,39 +7730,26 @@ fn switchExpr(
),
},
);
} else if (else_src) |some_else| {
return astgen.failNodeNotes(
node,
"else and '_' prong in switch expression",
.{},
&[_]u32{
try astgen.errNoteTok(
some_else,
"else prong here",
.{},
),
try astgen.errNoteTok(
case_src,
"'_' prong here",
.{},
),
},
);
}
if (case.inline_token != null) {
return astgen.failTok(case_src, "cannot inline '_' prong", .{});
return astgen.failTok(val_src, "cannot inline '_' prong", .{});
}
special_node = case_node.toOptional();
special_prong = if (case.ast.values.len == 1) .under else .absorbing_under;
underscore_src = case_src;
underscore_case_node = case_node.toOptional();
underscore_src = val_src;
underscore_node = val.toOptional();
found_underscore = true;
underscore_additional_items = switch (case.ast.values.len) {
0 => unreachable,
1 => .none,
2 => .one,
else => .many,
};
case_has_underscore = true;
},
.string_literal => return astgen.failNode(val, "cannot switch on strings", .{}),
else => {},
}
}
if (found_underscore) continue;
if (case_has_underscore) continue;
if (case.ast.values.len == 1 and tree.nodeTag(case.ast.values[0]) != .switch_range) {
scalar_cases_len += 1;
@@ -7791,6 +7761,14 @@ fn switchExpr(
}
}
const special_prongs: Zir.SpecialProngs = .init(
else_src != null,
underscore_src != null,
underscore_additional_items,
);
const has_else = special_prongs.hasElse();
const has_under = special_prongs.hasUnder();
const operand_ri: ResultInfo = .{ .rl = if (any_payload_is_ref) .ref else .none };
astgen.advanceSourceCursorToNode(operand_node);
@@ -7811,7 +7789,9 @@ fn switchExpr(
const payloads = &astgen.scratch;
const scratch_top = astgen.scratch.items.len;
const case_table_start = scratch_top;
const scalar_case_table = case_table_start + @intFromBool(special_prong != .none);
const else_case_index = if (has_else) case_table_start else undefined;
const under_case_index = if (has_under) case_table_start + @intFromBool(has_else) else undefined;
const scalar_case_table = case_table_start + @intFromBool(has_else) + @intFromBool(has_under);
const multi_case_table = scalar_case_table + scalar_cases_len;
const case_table_end = multi_case_table + multi_cases_len;
try astgen.scratch.resize(gpa, case_table_end);
@@ -7943,9 +7923,19 @@ fn switchExpr(
const header_index: u32 = @intCast(payloads.items.len);
const body_len_index = if (is_multi_case) blk: {
if (case_node.toOptional() == special_node) {
assert(special_prong == .absorbing_under);
payloads.items[case_table_start] = header_index;
if (case_node.toOptional() == underscore_case_node) {
payloads.items[under_case_index] = header_index;
if (special_prongs.hasOneAdditionalItem()) {
try payloads.resize(gpa, header_index + 2); // item, body_len
const maybe_item_node = case.ast.values[0];
const item_node = if (maybe_item_node.toOptional() == underscore_node)
case.ast.values[1]
else
maybe_item_node;
const item_inst = try comptimeExpr(parent_gz, scope, item_ri, item_node, .switch_item);
payloads.items[header_index] = @intFromEnum(item_inst);
break :blk header_index + 1;
}
} else {
payloads.items[multi_case_table + multi_case_index] = header_index;
multi_case_index += 1;
@@ -7985,9 +7975,13 @@ fn switchExpr(
payloads.items[header_index] = items_len;
payloads.items[header_index + 1] = ranges_len;
break :blk header_index + 2;
} else if (case_node.toOptional() == special_node) blk: {
assert(special_prong != .absorbing_under);
payloads.items[case_table_start] = header_index;
} else if (case_node.toOptional() == else_case_node) blk: {
payloads.items[else_case_index] = header_index;
try payloads.resize(gpa, header_index + 1); // body_len
break :blk header_index;
} else if (case_node.toOptional() == underscore_case_node) blk: {
assert(!special_prongs.hasAdditionalItems());
payloads.items[under_case_index] = header_index;
try payloads.resize(gpa, header_index + 1); // body_len
break :blk header_index;
} else blk: {
@@ -8048,7 +8042,7 @@ fn switchExpr(
.operand = raw_operand,
.bits = Zir.Inst.SwitchBlock.Bits{
.has_multi_cases = multi_cases_len != 0,
.special_prong = special_prong,
.special_prongs = special_prongs,
.any_has_tag_capture = any_has_tag_capture,
.any_non_inline_capture = any_non_inline_capture,
.has_continue = switch_full.label_token != null and block_scope.label.?.used_for_continue,
@@ -8067,29 +8061,40 @@ fn switchExpr(
const zir_datas = astgen.instructions.items(.data);
zir_datas[@intFromEnum(switch_block)].pl_node.payload_index = payload_index;
var normal_case_table_start = case_table_start;
if (special_prong != .none) {
normal_case_table_start += 1;
const start_index = payloads.items[case_table_start];
if (has_else) {
const start_index = payloads.items[else_case_index];
var end_index = start_index + 1;
const prong_info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(payloads.items[start_index]);
end_index += prong_info.body_len;
astgen.extra.appendSliceAssumeCapacity(payloads.items[start_index..end_index]);
}
if (has_under) {
const start_index = payloads.items[under_case_index];
var body_len_index = start_index;
var end_index = start_index;
if (special_prong == .absorbing_under) {
body_len_index += 2;
const items_len = payloads.items[start_index];
const ranges_len = payloads.items[start_index + 1];
end_index += 3 + items_len + 2 * ranges_len;
} else {
end_index += 1;
switch (underscore_additional_items) {
.none => {
end_index += 1;
},
.one => {
body_len_index += 1;
end_index += 2;
},
.many => {
body_len_index += 2;
const items_len = payloads.items[start_index];
const ranges_len = payloads.items[start_index + 1];
end_index += 3 + items_len + 2 * ranges_len;
},
}
const prong_info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(payloads.items[body_len_index]);
end_index += prong_info.body_len;
astgen.extra.appendSliceAssumeCapacity(payloads.items[start_index..end_index]);
}
for (payloads.items[normal_case_table_start..case_table_end], 0..) |start_index, i| {
for (payloads.items[scalar_case_table..case_table_end], 0..) |start_index, i| {
var body_len_index = start_index;
var end_index = start_index;
const table_index = normal_case_table_start + i;
const table_index = scalar_case_table + i;
if (table_index < multi_case_table) {
body_len_index += 1;
end_index += 2;

135
lib/std/zig/Zir.zig
View File

@@ -3226,9 +3226,14 @@ pub const Inst = struct {
/// 0. multi_cases_len: u32 // If has_multi_cases is set.
/// 1. tag_capture_inst: u32 // If any_has_tag_capture is set. Index of instruction prongs use to refer to the inline tag capture.
/// 2. else_body { // If special_prong != .none
/// items_len: u32, // If special_prong == .absorbing_under
/// ranges_len: u32, // If special_prong == .absorbing_under
/// 2. else_body { // If special_prong.hasElse() is set.
/// info: ProngInfo,
/// body member Index for every info.body_len
/// }
/// 3. under_body { // If special_prong.hasUnder() is set.
/// item: Ref, // If special_prong.hasOneAdditionalItem() is set.
/// items_len: u32, // If special_prong.hasManyAdditionalItems() is set.
/// ranges_len: u32, // If special_prong.hasManyAdditionalItems() is set.
/// info: ProngInfo,
/// item: Ref, // for every items_len
/// ranges: { // for every ranges_len
@@ -3237,12 +3242,12 @@ pub const Inst = struct {
/// }
/// body member Index for every info.body_len
/// }
/// 3. scalar_cases: { // for every scalar_cases_len
/// 4. scalar_cases: { // for every scalar_cases_len
/// item: Ref,
/// info: ProngInfo,
/// body member Index for every info.body_len
/// }
/// 4. multi_cases: { // for every multi_cases_len
/// 5. multi_cases: { // for every multi_cases_len
/// items_len: u32,
/// ranges_len: u32,
/// info: ProngInfo,
@@ -3283,16 +3288,17 @@ pub const Inst = struct {
/// If true, one or more prongs have multiple items.
has_multi_cases: bool,
/// Information about the special prong.
special_prong: SpecialProng,
special_prongs: SpecialProngs,
/// If true, at least one prong has an inline tag capture.
any_has_tag_capture: bool,
/// If true, at least one prong has a capture which may not
/// be comptime-known via `inline`.
any_non_inline_capture: bool,
/// If true, at least one prong contains a `continue`.
has_continue: bool,
scalar_cases_len: ScalarCasesLen,
pub const ScalarCasesLen = u26;
pub const ScalarCasesLen = u25;
};
pub const MultiProng = struct {
@@ -3868,17 +3874,67 @@ pub const Inst = struct {
};
};
pub const SpecialProng = enum(u2) {
none,
/// Simple else prong.
/// `else => {}`
@"else",
/// Simple '_' prong.
/// `_ => {}`
under,
/// '_' prong with additional items.
/// `a, _, b => {}`
absorbing_under,
pub const SpecialProngs = enum(u3) {
none = 0b000,
/// Simple `else` prong.
/// `else => {},`
@"else" = 0b001,
/// Simple `_` prong.
/// `_ => {},`
under = 0b010,
/// Both an `else` and a `_` prong.
/// `else => {},`
/// `_ => {},`
under_and_else = 0b011,
/// `_` prong with 1 additional item.
/// `a, _ => {},`
under_one_item = 0b100,
/// Both an `else` and a `_` prong with 1 additional item.
/// `else => {},`
/// `a, _ => {},`
under_one_item_and_else = 0b101,
/// `_` prong with >1 additional items.
/// `a, _, b => {},`
under_many_items = 0b110,
/// Both an `else` and a `_` prong with >1 additional items.
/// `else => {},`
/// `a, _, b => {},`
under_many_items_and_else = 0b111,
pub const AdditionalItems = enum(u3) {
none = @intFromEnum(SpecialProngs.under),
one = @intFromEnum(SpecialProngs.under_one_item),
many = @intFromEnum(SpecialProngs.under_many_items),
};
pub fn init(has_else: bool, has_under: bool, additional_items: AdditionalItems) SpecialProngs {
const else_bit: u3 = @intFromBool(has_else);
const under_bits: u3 = if (has_under)
@intFromEnum(additional_items)
else
@intFromEnum(SpecialProngs.none);
return @enumFromInt(else_bit | under_bits);
}
pub fn hasElse(special_prongs: SpecialProngs) bool {
return (@intFromEnum(special_prongs) & 0b001) != 0;
}
pub fn hasUnder(special_prongs: SpecialProngs) bool {
return (@intFromEnum(special_prongs) & 0b110) != 0;
}
pub fn hasAdditionalItems(special_prongs: SpecialProngs) bool {
return (@intFromEnum(special_prongs) & 0b100) != 0;
}
pub fn hasOneAdditionalItem(special_prongs: SpecialProngs) bool {
return (@intFromEnum(special_prongs) & 0b110) == @intFromEnum(SpecialProngs.under_one_item);
}
pub fn hasManyAdditionalItems(special_prongs: SpecialProngs) bool {
return (@intFromEnum(special_prongs) & 0b110) == @intFromEnum(SpecialProngs.under_many_items);
}
};
pub const DeclIterator = struct {
@@ -4723,7 +4779,7 @@ fn findTrackableSwitch(
}
const has_special = switch (kind) {
.normal => extra.data.bits.special_prong != .none,
.normal => extra.data.bits.special_prongs != .none,
.err_union => has_special: {
// Handle `non_err_body` first.
const prong_info: Inst.SwitchBlock.ProngInfo = @bitCast(zir.extra[extra_index]);
@@ -4738,29 +4794,40 @@ fn findTrackableSwitch(
};
if (has_special) {
const has_else = if (kind == .normal)
extra.data.bits.special_prongs.hasElse()
else
true;
if (has_else) {
const prong_info: Inst.SwitchBlock.ProngInfo = @bitCast(zir.extra[extra_index]);
extra_index += 1;
const body = zir.bodySlice(extra_index, prong_info.body_len);
extra_index += body.len;
try zir.findTrackableBody(gpa, contents, defers, body);
}
if (kind == .normal) {
if (extra.data.bits.special_prong == .absorbing_under) {
const items_len = zir.extra[extra_index];
extra_index += 1;
const ranges_len = zir.extra[extra_index];
extra_index += 1;
const prong_info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(zir.extra[extra_index]);
extra_index += 1;
extra_index += items_len + ranges_len * 2;
const special_prongs = extra.data.bits.special_prongs;
if (special_prongs.hasUnder()) {
var trailing_items_len: u32 = 0;
if (special_prongs.hasOneAdditionalItem()) {
extra_index += 1;
} else if (special_prongs.hasManyAdditionalItems()) {
const items_len = zir.extra[extra_index];
extra_index += 1;
const ranges_len = zir.extra[extra_index];
extra_index += 1;
trailing_items_len = items_len + ranges_len * 2;
}
const prong_info: Inst.SwitchBlock.ProngInfo = @bitCast(zir.extra[extra_index]);
extra_index += 1 + trailing_items_len;
const body = zir.bodySlice(extra_index, prong_info.body_len);
extra_index += body.len;
try zir.findTrackableBody(gpa, contents, defers, body);
}
}
const prong_info: Inst.SwitchBlock.ProngInfo = @bitCast(zir.extra[extra_index]);
extra_index += 1;
const body = zir.bodySlice(extra_index, prong_info.body_len);
extra_index += body.len;
try zir.findTrackableBody(gpa, contents, defers, body);
}
{