| author |  Matthew Lugg <mlugg@mlugg.co.uk> 2025-03-31 09:11:18+01:00 |
| committer |  Alex Rønne Petersen <alex@alexrp.com> 2025-04-02 08:43:13+02:00 |
| log | f5e7850686a0630015f26cc7f60e9d860a7dd05f |
| tree | 5f1c2aeffdcf487ed4661e3bc7282386042155dd |
| parent | 6ecd14321208e5f4562c2d4e4883aa46423ac725 |
| signature |  Signed by SSH key SHA256:7B/LJ7bpR1eX8aCXSr4mtd5M45VMPKcx9zY8e95b5QM |
Sema: allow `@ptrCast` slice of zero-bit type to slice of non-zero-bit type
This is actually completely well-defined. The resulting slice always has
0 elements. The only disallowed case is casting *to* a slice of a
zero-bit type, because in that case, you cna't figure out how many
destination elements to use (and there's *no* valid destination length
if the source slice corresponds to more than 0 bits).2 files changed, 25 insertions(+), 2 deletions(-)
src- test
- behavior
src/Sema.zig+5-2
| ... | ... | @@ -23488,11 +23488,14 @@ fn ptrCastFull( |
| 23488 | 23488 | if (src_slice_like_elem.comptimeOnly(zcu) or dest_elem.comptimeOnly(zcu)) { |
| 23489 | 23489 | return sema.fail(block, src, "cannot infer length of slice of '{}' from slice of '{}'", .{ dest_elem.fmt(pt), src_slice_like_elem.fmt(pt) }); |
| 23490 | 23490 | } |
| 23491 | const src_elem_size = src_slice_like_elem.abiSize(zcu); | |
| 23491 | // It's okay for `src_slice_like_elem` to be 0-bit; the resulting slice will just always have 0 elements. | |
| 23492 | // However, `dest_elem` can't be 0-bit. If it were, then either the source slice has 0 bits and we don't | |
| 23493 | // know how what `result.len` should be, or the source has >0 bits and there is no valid `result.len`. | |
| 23492 | 23494 | const dest_elem_size = dest_elem.abiSize(zcu); |
| 23493 | if (src_elem_size == 0 or dest_elem_size == 0) { | |
| 23495 | if (dest_elem_size == 0) { | |
| 23494 | 23496 | return sema.fail(block, src, "cannot infer length of slice of '{}' from slice of '{}'", .{ dest_elem.fmt(pt), src_slice_like_elem.fmt(pt) }); |
| 23495 | 23497 | } |
| 23498 | const src_elem_size = src_slice_like_elem.abiSize(zcu); | |
| 23496 | 23499 | break :need_len_change src_elem_size != dest_elem_size; |
| 23497 | 23500 | } else false; |
| 23498 | 23501 |
test/behavior/ptrcast.zig+20
| ... | ... | @@ -509,3 +509,23 @@ test "@ptrCast array pointer to slice with complex length decrease" { |
| 509 | 509 | try S.doTheTest(@splat(0)); |
| 510 | 510 | try comptime S.doTheTest(@splat(0)); |
| 511 | 511 | } |
| 512 | ||
| 513 | test "@ptrCast slice of zero-bit type to different slice" { | |
| 514 | if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO | |
| 515 | if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO | |
| 516 | if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO | |
| 517 | if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest; | |
| 518 | ||
| 519 | const S = struct { | |
| 520 | fn doTheTest(comptime T: type, zero_bits: []const T) !void { | |
| 521 | const out: []const u8 = @ptrCast(zero_bits); | |
| 522 | try expect(out.len == 0); | |
| 523 | } | |
| 524 | }; | |
| 525 | try S.doTheTest(void, &.{ {}, {}, {} }); | |
| 526 | try S.doTheTest(u0, &.{ 0, 0, 0, 0 }); | |
| 527 | try S.doTheTest(packed struct(u0) {}, &.{ .{}, .{} }); | |
| 528 | try comptime S.doTheTest(void, &.{ {}, {}, {} }); | |
| 529 | try comptime S.doTheTest(u0, &.{ 0, 0, 0, 0 }); | |
| 530 | try comptime S.doTheTest(packed struct(u0) {}, &.{ .{}, .{} }); | |
| 531 | } |