From 3e084d8de352927dad182f99aeb3f166b348c192 Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Thu, 5 Jan 2023 13:43:06 +0200
Subject: [PATCH] Sema: only untyped undefined should coerce to all types

Closes #13958
---
 src/Sema.zig                                          |  2 +-
 .../only_untyped_undef_coerces_to_all_types.zig       | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 test/cases/compile_errors/only_untyped_undef_coerces_to_all_types.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 657ca331b2..bc861f170a 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -24477,7 +24477,7 @@ fn coerceExtra(
         return block.addBitCast(dest_ty, inst);
     }
 
-    const is_undef = if (maybe_inst_val) |val| val.isUndef() else false;
+    const is_undef = inst_ty.zigTypeTag() == .Undefined;
 
     switch (dest_ty.zigTypeTag()) {
         .Optional => optional: {
diff --git a/test/cases/compile_errors/only_untyped_undef_coerces_to_all_types.zig b/test/cases/compile_errors/only_untyped_undef_coerces_to_all_types.zig
new file mode 100644
index 0000000000..091c51ff3b
--- /dev/null
+++ b/test/cases/compile_errors/only_untyped_undef_coerces_to_all_types.zig
@@ -0,0 +1,11 @@
+pub export fn entry() void {
+    const x: []u8 = undefined;
+    const y: f32 = x;
+    _ = y;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:20: error: expected type 'f32', found '[]u8'