From ea599150cd8f9c7f8c737160f0165ce5c8e11134 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Thu, 12 Feb 2026 20:35:58 +0000
Subject: [PATCH] astgen: implement error set declarations

Port errorSetDecl from upstream AstGen.zig:5905-5955. Replaces the
SET_ERROR placeholder at the ERROR_SET_DECL case. Loops tokens between
lbrace and rbrace, collecting identifier strings into the ErrorSetDecl
payload.

Also add error_set_decl to the test comparison functions.

Tests added: empty error set, error set with members.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 astgen.c        | 29 +++++++++++++++++++++++++----
 astgen_test.zig | 26 ++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/astgen.c b/astgen.c
index d764f577cb..7833a720c9 100644
--- a/astgen.c
+++ b/astgen.c
@@ -3476,11 +3476,32 @@ static uint32_t exprRl(GenZir* gz, Scope* scope, ResultLoc rl, uint32_t node) {
         return rvalue(gz, rl,
             addStrTok(gz, ZIR_INST_ERROR_VALUE, str, error_token), node);
     }
-    // error_set_decl (AstGen.zig:1131-1140).
+    // error_set_decl (AstGen.zig:5905-5955).
     case AST_NODE_ERROR_SET_DECL: {
-        // TODO: proper error set, for now just emit a placeholder.
-        SET_ERROR(ag);
-        return ZIR_REF_VOID_VALUE;
+        AstData esd = ag->tree->nodes.datas[node];
+        uint32_t lbrace = esd.lhs;
+        uint32_t rbrace = esd.rhs;
+        // Reserve 1 extra word for ErrorSetDecl.fields_len.
+        ensureExtraCapacity(ag, 1 + (rbrace - lbrace));
+        uint32_t payload_index = ag->extra_len;
+        ag->extra_len++; // placeholder for fields_len
+        uint32_t fields_len = 0;
+        for (uint32_t tok = lbrace + 1; tok < rbrace; tok++) {
+            TokenizerTag ttag = ag->tree->tokens.tags[tok];
+            if (ttag == TOKEN_DOC_COMMENT || ttag == TOKEN_COMMA)
+                continue;
+            if (ttag == TOKEN_IDENTIFIER) {
+                uint32_t str_index = identAsString(ag, tok);
+                ensureExtraCapacity(ag, 1);
+                ag->extra[ag->extra_len++] = str_index;
+                fields_len++;
+            }
+        }
+        ag->extra[payload_index] = fields_len;
+        return rvalue(gz, rl,
+            addPlNodePayloadIndex(
+                gz, ZIR_INST_ERROR_SET_DECL, node, payload_index),
+            node);
     }
     // assign in expr context (AstGen.zig:1011-1014).
     case AST_NODE_ASSIGN:
diff --git a/astgen_test.zig b/astgen_test.zig
index d162142233..93213dfb3b 100644
--- a/astgen_test.zig
+++ b/astgen_test.zig
@@ -472,6 +472,7 @@ fn expectEqualData(
         .array_cat,
         .array_init,
         .array_init_ref,
+        .error_set_decl,
         => {
             const r = ref.pl_node;
             const g = got.pl_node;
@@ -780,6 +781,7 @@ fn dataMatches(tag: Zir.Inst.Tag, ref: Zir.Inst.Data, got: c.ZirInstData) bool {
         .array_cat,
         .array_init,
         .array_init_ref,
+        .error_set_decl,
         => {
             return @intFromEnum(ref.pl_node.src_node) == got.pl_node.src_node and
                 ref.pl_node.payload_index == got.pl_node.payload_index;
@@ -908,6 +910,30 @@ test "astgen: struct comptime field" {
     try expectEqualZir(gpa, ref_zir, c_zir);
 }
 
+test "astgen: empty error set" {
+    const gpa = std.testing.allocator;
+    const source: [:0]const u8 = "const E = error{};";
+    var ref_zir = try refZir(gpa, source);
+    defer ref_zir.deinit(gpa);
+    var c_ast = c.astParse(source.ptr, @intCast(source.len));
+    defer c.astDeinit(&c_ast);
+    var c_zir = c.astGen(&c_ast);
+    defer c.zirDeinit(&c_zir);
+    try expectEqualZir(gpa, ref_zir, c_zir);
+}
+
+test "astgen: error set with members" {
+    const gpa = std.testing.allocator;
+    const source: [:0]const u8 = "const E = error{ OutOfMemory, OutOfTime };";
+    var ref_zir = try refZir(gpa, source);
+    defer ref_zir.deinit(gpa);
+    var c_ast = c.astParse(source.ptr, @intCast(source.len));
+    defer c.astDeinit(&c_ast);
+    var c_zir = c.astGen(&c_ast);
+    defer c.zirDeinit(&c_zir);
+    try expectEqualZir(gpa, ref_zir, c_zir);
+}
+
 test "astgen: corpus test_all.zig" {
     const gpa = std.testing.allocator;
     try corpusCheck(gpa, "test_all.zig", @embedFile("test_all.zig"));