zig

commit fecd28371d5c0e25357dfb91f75c8790f8b4155b (tree)
parent fc1c83a363d32e749b9061044db63852ab7255d0
Author: Matthew Lugg <mlugg@mlugg.co.uk>
Date:   Wed,  6 May 2026 11:21:40 +0100

Sema: fix crash bitcasting undefined to bitpack type

Resolves: https://codeberg.org/ziglang/zig/issues/31944

Diffstat:
M
src/Sema/bitcast.zig
 | 
2
++
M
test/behavior/packed-struct.zig
 | 
6
++++++
M
test/behavior/packed-union.zig
 | 
6
++++++

3 files changed, 14 insertions(+), 0 deletions(-)
diff --git a/src/Sema/bitcast.zig b/src/Sema/bitcast.zig
@@ -565,6 +565,7 @@ const PackValueBits = struct {
                 },
                 .@"packed" => {
                     const backing_int_val = try pack.primitive(ty.bitpackBackingInt(zcu));
+                    if (backing_int_val.isUndef(zcu)) return pt.undefValue(ty);
                     return pt.bitpackValue(ty, backing_int_val);
                 },
             },
@@ -659,6 +660,7 @@ const PackValueBits = struct {
                 },
                 .@"packed" => {
                     const backing_int_val = try pack.primitive(ty.bitpackBackingInt(zcu));
+                    if (backing_int_val.isUndef(zcu)) return pt.undefValue(ty);
                     return pt.bitpackValue(ty, backing_int_val);
                 },
             },
diff --git a/test/behavior/packed-struct.zig b/test/behavior/packed-struct.zig
@@ -1240,3 +1240,9 @@ test "packed struct store of comparison result" {
     try expect(result2.a);
     try expect(!result2.b);
 }
+
+test "initialize packed struct field to undefined at comptime" {
+    const S = packed struct(u8) { x: u8 };
+    const val: S = .{ .x = undefined };
+    _ = val;
+}
diff --git a/test/behavior/packed-union.zig b/test/behavior/packed-union.zig
@@ -219,3 +219,9 @@ test "packed union equality" {
     try S.doTest(x, y);
     comptime try S.doTest(x, y);
 }
+
+test "initialize packed union field to undefined at comptime" {
+    const U = packed union(u8) { x: u8 };
+    const val: U = .{ .x = undefined };
+    _ = val;
+}