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lint: use transparent_newtype_field to avoid ICE #74340

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Jul 14, 2020
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lint: use transparent_newtype_field to avoid ICE #74340

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32 changes: 16 additions & 16 deletions src/librustc_lint/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -531,23 +531,23 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
match ty.kind {
ty::FnPtr(_) => true,
ty::Ref(..) => true,
ty::Adt(field_def, substs) if field_def.repr.transparent() && !field_def.is_union() => {
for field in field_def.all_fields() {
let field_ty = self.cx.tcx.normalize_erasing_regions(
self.cx.param_env,
field.ty(self.cx.tcx, substs),
);
if field_ty.is_zst(self.cx.tcx, field.did) {
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What does is_zst even do? I'm surprised to see that method on Ty, and suspicious of how it might be implemented.

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I added it in an earlier PR (or I just made it with existing logic, I forget), it’s predominantly used in lints which care about transparent types. Its logic is the same as where transparent types are checked in typeck (but it wasn’t trivial to factor it out there too) - it basically gets the layout of the type and calls is_zst on that, returning false if any of the intermediate stuff fails.

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I don't think Ty should have methods that interact with layout, feels like an abstraction violation.
If something relies on layout that should be clear (i.e. is_zst callers should use layout_of themselves - not to mention that e.g. LateLintContext should have better layout_of integration than doing it on Ty)

continue;
}
ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
let guaranteed_nonnull_optimization = self
.cx
.tcx
.get_attrs(def.did)
.iter()
.any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed));

if guaranteed_nonnull_optimization {
return true;
}

let attrs = self.cx.tcx.get_attrs(field_def.did);
if attrs
.iter()
.any(|a| a.check_name(sym::rustc_nonnull_optimization_guaranteed))
|| self.ty_is_known_nonnull(field_ty)
{
return true;
for variant in &def.variants {
if let Some(field) = variant.transparent_newtype_field(self.cx.tcx) {
if self.ty_is_known_nonnull(field.ty(self.cx.tcx, substs)) {
return true;
}
}
}

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14 changes: 14 additions & 0 deletions src/test/ui/lint/lint-ctypes-73747.rs
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@@ -0,0 +1,14 @@
// check-pass

#[repr(transparent)]
struct NonNullRawComPtr<T: ComInterface> {
inner: std::ptr::NonNull<<T as ComInterface>::VTable>,
}

trait ComInterface {
type VTable;
}

extern "C" fn invoke<T: ComInterface>(_: Option<NonNullRawComPtr<T>>) {}

fn main() {}