From 3031d813874f6d6ad9ae4b793e3af6cdf632fa66 Mon Sep 17 00:00:00 2001
From: mlugg <mlugg@mlugg.co.uk>
Date: Wed, 5 Feb 2025 21:26:04 +0000
Subject: [PATCH] Sema: fix `@typeInfo` of function with generic return type
 and IES

Resolves: #20088
---
 src/Sema.zig                | 14 ++++++++++----
 test/behavior/type_info.zig |  9 +++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 32f611ce3e..5f92e12b04 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -18145,10 +18145,16 @@ fn zirTypeInfo(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
 
             const ret_ty_opt = try pt.intern(.{ .opt = .{
                 .ty = try pt.intern(.{ .opt_type = .type_type }),
-                .val = if (func_ty_info.return_type == .generic_poison_type)
-                    .none
-                else
-                    func_ty_info.return_type,
+                .val = opt_val: {
+                    const ret_ty: Type = .fromInterned(func_ty_info.return_type);
+                    if (ret_ty.toIntern() == .generic_poison_type) break :opt_val .none;
+                    if (ret_ty.zigTypeTag(zcu) == .error_union) {
+                        if (ret_ty.errorUnionPayload(zcu).toIntern() == .generic_poison_type) {
+                            break :opt_val .none;
+                        }
+                    }
+                    break :opt_val ret_ty.toIntern();
+                },
             } });
 
             const callconv_ty = try sema.getBuiltinType(src, .CallingConvention);
diff --git a/test/behavior/type_info.zig b/test/behavior/type_info.zig
index 2b7a66c763..86e2eccc4c 100644
--- a/test/behavior/type_info.zig
+++ b/test/behavior/type_info.zig
@@ -675,3 +675,12 @@ test "@typeInfo only contains pub decls" {
     try std.testing.expectEqualStrings("Enum", decls[0].name);
     try std.testing.expectEqualStrings("Struct", decls[1].name);
 }
+
+test "@typeInfo function with generic return type and inferred error set" {
+    const S = struct {
+        fn testFn(comptime T: type) !T {}
+    };
+
+    const ret_ty = @typeInfo(@TypeOf(S.testFn)).@"fn".return_type;
+    comptime assert(ret_ty == null);
+}