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warn less about non-exhaustive in ffi

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Bindgen allows generating `#[non_exhaustive] #[repr(u32)]` enums.
This results in nonintuitive nonlocal `improper_ctypes` warnings,
even when the types are otherwise perfectly valid in C.

Adjust for actual tooling expectations by avoiding warning on
simple enums with only unit variants.
This commit is contained in:
Jubilee Young 2023-10-16 23:56:22 -07:00
parent 749f80ab05
commit e9cf280ef2
4 changed files with 43 additions and 15 deletions
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27
compiler/rustc_lint/src/types.rs
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@ -3,6 +3,7 @@ use std::ops::ControlFlow;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::DiagMessage;
use rustc_hir::def::CtorKind;
use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
use rustc_middle::bug;
use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
@ -1386,15 +1387,6 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
// Empty enums are okay... although sort of useless.
return FfiSafe;
}
if def.is_variant_list_non_exhaustive() && !def.did().is_local() {
return FfiUnsafe {
ty,
reason: fluent::lint_improper_ctypes_non_exhaustive,
help: None,
};
}
// Check for a repr() attribute to specify the size of the
// discriminant.
if !def.repr().c() && !def.repr().transparent() && def.repr().int.is_none()
@ -1413,8 +1405,25 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
};
}
// non_exhaustive suggests it is possible that someone might break ABI
// see: https://github.com/rust-lang/rust/issues/44109#issuecomment-537583344
// so warn on complex enums being used outside their crate
let nonexhaustive_nonlocal_ffi =
def.is_variant_list_non_exhaustive() && !def.did().is_local();
// Check the contained variants.
for variant in def.variants() {
// but only warn about really_tagged_union reprs,
// exempt enums with unit ctors like C's (like rust-bindgen)
if nonexhaustive_nonlocal_ffi
&& !matches!(variant.ctor_kind(), Some(CtorKind::Const))
{
return FfiUnsafe {
ty,
reason: fluent::lint_improper_ctypes_non_exhaustive,
help: None,
};
};
let is_non_exhaustive = variant.is_field_list_non_exhaustive();
if is_non_exhaustive && !variant.def_id.is_local() {
return FfiUnsafe {