zig

commit 8111d3d63cf3662b5aecbd0ddd10567e025694a7 (tree)
parent 2c6e5006ed3adb02f3bc7b364b2bbc688271d9f7
Author: glowsquid <sachabarsayuracko@gmail.com>
Date:   Fri, 10 Apr 2026 23:31:21 +0200

fix comptime @ptrcasting from a larger type to a smaller one (#31774)

closes #30180

Note from mlugg: this fix is very much a hack, but it definitely won't break anything and it demonstrably fixes one case, so I'm merging it for now with the expectation that I'll be replacing the broken code soon.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31774
Reviewed-by: mlugg <mlugg@noreply.codeberg.org>
Co-authored-by: glowsquid <sachabarsayuracko@gmail.com>
Co-committed-by: glowsquid <sachabarsayuracko@gmail.com>

Diffstat:
M
src/Sema/comptime_ptr_access.zig
 | 
12
+++++++++++-
M
test/behavior/ptrcast.zig
 | 
8
++++++++

2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/src/Sema/comptime_ptr_access.zig b/src/Sema/comptime_ptr_access.zig
@@ -498,8 +498,18 @@ fn loadComptimePtrInner(
         return .{ .success = cur_val };
     }
 
+    var bitcast_src_val = try cur_val.intern(sema.pt, sema.arena);
+
+    if (host_bits != 0) {
+        const src_bit_size = bitcast_src_val.typeOf(zcu).bitSize(zcu);
+        if (src_bit_size > host_bits) {
+            const truncate_ty = try pt.intType(.unsigned, @intCast(host_bits));
+            bitcast_src_val = try pt.getCoerced(bitcast_src_val, truncate_ty);
+        }
+    }
+
     const result_val = try sema.bitCastVal(
-        try cur_val.intern(sema.pt, sema.arena),
+        bitcast_src_val,
         load_ty,
         cur_offset,
         host_bits,
diff --git a/test/behavior/ptrcast.zig b/test/behavior/ptrcast.zig
@@ -562,3 +562,11 @@ test "@ptrCast array pointer removing sentinel" {
     comptime assert(out[2] == 3);
     comptime assert(out[3] == 4);
 }
+
+test "@ptrcast larger type to smaller one" {
+    const T = packed struct { x: u17 };
+    const a: u32 = 0;
+    const b: *const T = @ptrCast(&a);
+    const c = b.x;
+    _ = c;
+}