Commit 27274d4fdea8061d7afacbb2b179fd49fbaca125 | zig

author	Matthew Lugg <mlugg@mlugg.co.uk> 2025-01-12 23:45:22+00:00
committer	Matthew Lugg <mlugg@mlugg.co.uk> 2025-01-14 20:27:49+00:00
log	27274d4fdea8061d7afacbb2b179fd49fbaca125
tree	c822f893fc11d549384a3ba3942aa280011b69b3
parent	affe45b31f48d216a407f060c49df6bad82ad30c

Type: `struct {}` does not have a well-defined layout

`Type.hasWellDefinedLayout` was in disagreement with pointer loading
logic about auto-layout structs with zero fields, `struct {}`. For
consistency, these types should not have a well-defined layout.

This is technically a breaking change.

2 files changed, 12 insertions(+), 5 deletions(-)

src
- Type.zig
test
- cases
  - compile_errors
    dereference_bad_pointer_via_array_mul.zig

src/Type.zig+1-5

 @@ -723,11 +723,7 @@ pub fn hasWellDefinedLayout(ty: Type, zcu: *const Zcu) bool {
             .generic_poison,
             => false,
         },
-        .struct_type => {
+        .struct_type => ip.loadStructType(ty.toIntern()).layout != .auto,
-            const struct_type = ip.loadStructType(ty.toIntern());
-            // Struct with no fields have a well-defined layout of no bits.
-            return struct_type.layout != .auto or struct_type.field_types.len == 0;
-        },
         .union_type => {
             const union_type = ip.loadUnionType(ty.toIntern());
             return switch (union_type.flagsUnordered(ip).runtime_tag) {

test/cases/compile_errors/dereference_bad_pointer_via_array_mul.zig created+11

...	@@ -0,0 +1,11 @@
1	const A = struct {};
2	const B = struct {};
3	comptime {
4	const val: [1]A = .{.{}};
5	const ptr: *const [1]B = @ptrCast(&val);
6	_ = ptr ** 2;
7	}
8
9	// error
10	//
11	// :6:9: error: comptime dereference requires '[1]tmp.B' to have a well-defined layout