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Sema: match master's weird pointer difference semantics for now

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...except for master's handling of pointers to vectors, because that was
unambiguously a bug.
This commit is contained in:
Matthew Lugg 2026-03-02 15:45:35 +00:00
parent e415d725d3
commit e8e80cfa47
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1 changed files with 13 additions and 3 deletions
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src/Sema.zig
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@ -15249,15 +15249,25 @@ fn analyzeArithmetic(
return sema.failWithInvalidPtrArithmetic(block, src, "pointer-pointer", "subtraction");
}
// MLUGG TODO: these semantics are insane and matching them is causing my soul to fragment into a thousand pieces
// TODO: these semantics are really weird. Pointer subtraction works in increments
// of the pointer child for indexable pointers (excluding pointers to vectors),
// which makes sense, but we also allow it for arbitrary single-item pointers, which
// leads to the weird result that subtraction of '*T' works completely differently
// depending on whether 'T' is an array. That seems dangerous and confusing, and
// requires the odd logic below. This behavior originally came from a now-removed
// function `Type.elemType2`, which was removed precisely *because* the thing it did
// wasn't really well-defined; for that reason, these semantics were probably
// largely accidental to begin with. We should change the langauge to avoid this
// confusing behavior. For instance, perhaps pointer subtraction should only work on
// indexable pointers.
const lhs_elem_ty = ty: {
const ptr_elem_ty = lhs_ty.childType(zcu);
if (lhs_ty.ptrSize(zcu) == .one and ptr_elem_ty.isArrayOrVector(zcu)) break :ty ptr_elem_ty.childType(zcu);
if (lhs_ty.ptrSize(zcu) == .one and ptr_elem_ty.zigTypeTag(zcu) == .array) break :ty ptr_elem_ty.childType(zcu);
break :ty ptr_elem_ty;
};
const rhs_elem_ty = ty: {
const ptr_elem_ty = rhs_ty.childType(zcu);
if (rhs_ty.ptrSize(zcu) == .one and ptr_elem_ty.isArrayOrVector(zcu)) break :ty ptr_elem_ty.childType(zcu);
if (rhs_ty.ptrSize(zcu) == .one and ptr_elem_ty.zigTypeTag(zcu) == .array) break :ty ptr_elem_ty.childType(zcu);
break :ty ptr_elem_ty;
};
if (lhs_elem_ty.toIntern() != rhs_elem_ty.toIntern()) {