errorName: return a null-terminated slice

3 files changed, 19 insertions, 8 deletions

diff --git a/doc/langref.html.in b/doc/langref.html.in
index fcf07eb6c1..c7a677bb8e 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -7475,7 +7475,7 @@ test "main" {
       {#header_close#}
 
       {#header_open|@errorName#}
-      <pre>{#syntax#}@errorName(err: anyerror) []const u8{#endsyntax#}</pre>
+      <pre>{#syntax#}@errorName(err: anyerror) [:0]const u8{#endsyntax#}</pre>
       <p>
       This function returns the string representation of an error. The string representation
       of {#syntax#}error.OutOfMem{#endsyntax#} is {#syntax#}"OutOfMem"{#endsyntax#}.
diff --git a/src/stage1/ir.cpp b/src/stage1/ir.cpp
index 10dfb798cb..2200e8380d 100644
--- a/src/stage1/ir.cpp
+++ b/src/stage1/ir.cpp
@@ -16864,26 +16864,27 @@ static IrInstGen *ir_analyze_instruction_err_name(IrAnalyze *ira, IrInstSrcErrNa
     if (type_is_invalid(casted_value->value->type))
         return ira->codegen->invalid_inst_gen;
 
-    ZigType *u8_ptr_type = get_pointer_to_type_extra(ira->codegen, ira->codegen->builtin_types.entry_u8,
-            true, false, PtrLenUnknown, 0, 0, 0, false);
-    ZigType *str_type = get_slice_type(ira->codegen, u8_ptr_type);
     if (instr_is_comptime(casted_value)) {
         ZigValue *val = ir_resolve_const(ira, casted_value, UndefBad);
         if (val == nullptr)
             return ira->codegen->invalid_inst_gen;
         ErrorTableEntry *err = casted_value->value->data.x_err_set;
         if (!err->cached_error_name_val) {
-            ZigValue *array_val = create_const_str_lit(ira->codegen, &err->name)->data.x_ptr.data.ref.pointee;
-            err->cached_error_name_val = create_const_slice(ira->codegen, array_val, 0, buf_len(&err->name), true);
+            err->cached_error_name_val = create_sentineled_str_lit(
+                ira->codegen, &err->name,
+                ira->codegen->intern.for_zero_byte());
         }
         IrInstGen *result = ir_const(ira, &instruction->base.base, nullptr);
-        copy_const_val(ira->codegen, result->value, err->cached_error_name_val);
-        result->value->type = str_type;
+        result->value = err->cached_error_name_val;
         return result;
     }
 
     ira->codegen->generate_error_name_table = true;
 
+    ZigType *u8_ptr_type = get_pointer_to_type_extra2(ira->codegen, ira->codegen->builtin_types.entry_u8,
+            true, false, PtrLenUnknown, 0, 0, 0, false,
+            VECTOR_INDEX_NONE, nullptr, ira->codegen->intern.for_zero_byte());
+    ZigType *str_type = get_slice_type(ira->codegen, u8_ptr_type);
     return ir_build_err_name_gen(ira, &instruction->base.base, value, str_type);
 }
 
diff --git a/test/behavior/bugs/3779.zig b/test/behavior/bugs/3779.zig
index 8866b39de3..5423a6f265 100644
--- a/test/behavior/bugs/3779.zig
+++ b/test/behavior/bugs/3779.zig
@@ -9,3 +9,13 @@ test "@tagName() returns a string literal" {
     try std.testing.expectEqualStrings("TestEnumValue", tag_name);
     try std.testing.expectEqualStrings("TestEnumValue", ptr_tag_name[0..tag_name.len]);
 }
+
+const TestError = error{TestErrorCode};
+const error_name = @errorName(TestError.TestErrorCode);
+const ptr_error_name: [*:0]const u8 = error_name;
+
+test "@errorName() returns a string literal" {
+    try std.testing.expectEqual([:0]const u8, @TypeOf(error_name));
+    try std.testing.expectEqualStrings("TestErrorCode", error_name);
+    try std.testing.expectEqualStrings("TestErrorCode", ptr_error_name[0..error_name.len]);
+}