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Sema: exclude sentinel from source array length in pointer cast to slice

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Resolves: #24569
This commit is contained in:
mlugg 2025-07-25 18:59:35 +01:00 committed by Matthew Lugg
parent fc4b7c968a
commit c9ce1debe7
2 changed files with 24 additions and 8 deletions
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22
src/Sema.zig
View File

@ -22483,11 +22483,18 @@ fn ptrCastFull(
.slice => {}, .slice => {},
.many, .c, .one => break :len null, .many, .c, .one => break :len null,
} }
// `null` means the operand is a runtime-known slice (so the length is runtime-known). // A `null` length means the operand is a runtime-known slice (so the length is runtime-known).
const opt_src_len: ?u64 = switch (src_info.flags.size) { // `src_elem_type` is different from `src_info.child` if the latter is an array, to ensure we ignore sentinels.
.one => 1, const src_elem_ty: Type, const opt_src_len: ?u64 = switch (src_info.flags.size) {
.slice => src_len: { .one => src: {
const operand_val = try sema.resolveValue(operand) orelse break :src_len null; const true_child: Type = .fromInterned(src_info.child);
break :src switch (true_child.zigTypeTag(zcu)) {
.array => .{ true_child.childType(zcu), true_child.arrayLen(zcu) },
else => .{ true_child, 1 },
};
},
.slice => src: {
const operand_val = try sema.resolveValue(operand) orelse break :src .{ .fromInterned(src_info.child), null };
if (operand_val.isUndef(zcu)) break :len .undef; if (operand_val.isUndef(zcu)) break :len .undef;
const slice_val = switch (operand_ty.zigTypeTag(zcu)) { const slice_val = switch (operand_ty.zigTypeTag(zcu)) {
.optional => operand_val.optionalValue(zcu) orelse break :len .undef, .optional => operand_val.optionalValue(zcu) orelse break :len .undef,
@ -22496,14 +22503,13 @@ fn ptrCastFull(
}; };
const slice_len_resolved = try sema.resolveLazyValue(.fromInterned(zcu.intern_pool.sliceLen(slice_val.toIntern()))); const slice_len_resolved = try sema.resolveLazyValue(.fromInterned(zcu.intern_pool.sliceLen(slice_val.toIntern())));
if (slice_len_resolved.isUndef(zcu)) break :len .undef; if (slice_len_resolved.isUndef(zcu)) break :len .undef;
break :src_len slice_len_resolved.toUnsignedInt(zcu); break :src .{ .fromInterned(src_info.child), slice_len_resolved.toUnsignedInt(zcu) };
}, },
.many, .c => { .many, .c => {
return sema.fail(block, src, "cannot infer length of slice from {s}", .{pointerSizeString(src_info.flags.size)}); return sema.fail(block, src, "cannot infer length of slice from {s}", .{pointerSizeString(src_info.flags.size)});
}, },
}; };
const dest_elem_ty: Type = .fromInterned(dest_info.child); const dest_elem_ty: Type = .fromInterned(dest_info.child);
const src_elem_ty: Type = .fromInterned(src_info.child);
if (dest_elem_ty.toIntern() == src_elem_ty.toIntern()) { if (dest_elem_ty.toIntern() == src_elem_ty.toIntern()) {
break :len if (opt_src_len) |l| .{ .constant = l } else .equal_runtime_src_slice; break :len if (opt_src_len) |l| .{ .constant = l } else .equal_runtime_src_slice;
} }
@ -22519,7 +22525,7 @@ fn ptrCastFull(
const bytes = src_len * src_elem_size; const bytes = src_len * src_elem_size;
const dest_len = std.math.divExact(u64, bytes, dest_elem_size) catch switch (src_info.flags.size) { const dest_len = std.math.divExact(u64, bytes, dest_elem_size) catch switch (src_info.flags.size) {
.slice => return sema.fail(block, src, "slice length '{d}' does not divide exactly into destination elements", .{src_len}), .slice => return sema.fail(block, src, "slice length '{d}' does not divide exactly into destination elements", .{src_len}),
.one => return sema.fail(block, src, "type '{f}' does not divide exactly into destination elements", .{src_elem_ty.fmt(pt)}), .one => return sema.fail(block, src, "type '{f}' does not divide exactly into destination elements", .{Type.fromInterned(src_info.child).fmt(pt)}),
else => unreachable, else => unreachable,
}; };
break :len .{ .constant = dest_len }; break :len .{ .constant = dest_len };

10
test/behavior/ptrcast.zig
View File

@ -552,3 +552,13 @@ test "@ptrCast single-item pointer to slice of bytes" {
try comptime S.doTheTest(void, &{}); try comptime S.doTheTest(void, &{});
try comptime S.doTheTest(struct { x: u32 }, &.{ .x = 123 }); try comptime S.doTheTest(struct { x: u32 }, &.{ .x = 123 });
} }
test "@ptrCast array pointer removing sentinel" {
const in: *const [4:0]u8 = &.{ 1, 2, 3, 4 };
const out: []const i8 = @ptrCast(in);
comptime assert(out.len == 4);
comptime assert(out[0] == 1);
comptime assert(out[1] == 2);
comptime assert(out[2] == 3);
comptime assert(out[3] == 4);
}