| author |  Justus Klausecker <justus@klausecker.de> 2026-05-06 09:42:40+02:00 |
| committer |  Matthew Lugg <mlugg@mlugg.co.uk> 2026-05-07 06:25:43+02:00 |
| log | 6d0b8879728722d14561d747717f616cd4e7ae0c |
| tree | db3b272e121832e6b3eaddbd6ab84dea12725eec |
| parent | fecd28371d5c0e25357dfb91f75c8790f8b4155b |
Sema: disallow pointer cast from pointer to opaque type to slice
Fixes a regression where this conversion crashes. When the conversion was
still possible it would produce a slice with a length of zero, which doesn't
really make a lot of sense either. There's no way to determine the length
of the destination slice from a pointer to an opaque type, so it's a compile
error now. Users should just cast to a many-item pointer and slice to the
desired length manually instead.2 files changed, 24 insertions(+), 0 deletions(-)
src- test
- cases
- compile_errors
src/Sema.zig+10
| ... | ... | @@ -21154,6 +21154,16 @@ fn ptrCastFull( |
| 21154 | 21154 | break :len if (opt_src_len) |l| .{ .constant = l } else .equal_runtime_src_slice; |
| 21155 | 21155 | } |
| 21156 | 21156 | if (!src_elem_ty.comptimeOnly(zcu) and !dest_elem_ty.comptimeOnly(zcu)) { |
| 21157 | if (src_elem_ty.zigTypeTag(zcu) == .@"opaque") { | |
| 21158 | return sema.failWithOwnedErrorMsg(block, msg: { | |
| 21159 | const msg = try sema.errMsg(src, "cannot infer length of slice of '{f}' from pointer to opaque type '{f}' with unknown size", .{ | |
| 21160 | dest_elem_ty.fmt(pt), src_elem_ty.fmt(pt), | |
| 21161 | }); | |
| 21162 | errdefer msg.destroy(gpa); | |
| 21163 | try sema.addDeclaredHereNote(msg, src_elem_ty); | |
| 21164 | break :msg msg; | |
| 21165 | }); | |
| 21166 | } | |
| 21157 | 21167 | const src_elem_size = src_elem_ty.abiSize(zcu); |
| 21158 | 21168 | const dest_elem_size = dest_elem_ty.abiSize(zcu); |
| 21159 | 21169 | if (dest_elem_size == 0) { |
test/cases/compile_errors/ptrcast_anyopaque_to_slice.zig created+14
| ... | ... | @@ -0,0 +1,14 @@ |
| 1 | export fn entry1(x: *anyopaque) void { | |
| 2 | _ = @as([]u8, @ptrCast(x)); | |
| 3 | } | |
| 4 | ||
| 5 | const Opaque = opaque {}; | |
| 6 | export fn entry2(x: *Opaque) void { | |
| 7 | _ = @as([]u8, @ptrCast(x)); | |
| 8 | } | |
| 9 | ||
| 10 | // error | |
| 11 | // | |
| 12 | // :2:19: error: cannot infer length of slice of 'u8' from pointer to opaque type 'anyopaque' with unknown size | |
| 13 | // :7:19: error: cannot infer length of slice of 'u8' from pointer to opaque type 'tmp.Opaque' with unknown size | |
| 14 | // :5:16: note: opaque declared here |