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Auto merge of #138892 - compiler-errors:revert-ptr-ptr, r=oli-obk

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Revert "Rollup merge of #136127 - WaffleLapkin:dyn_ptr_unwrap_cast, r=compiler-errors"

...not permanently tho. Just until we can land something like #138542, which will fix the underlying perf issues (https://github.com/rust-lang/rust/pull/136127#issuecomment-2743891744). I just don't want this to land on beta and have people rely on this behavior if it'll need some reworking for it to be implemented performantly.

r? `@WaffleLapkin` or reassign -- sorry for reverting ur pr! i'm working on getting it re-landed soon :>
This commit is contained in:
bors 2025-03-31 11:58:58 +00:00
commit ab5b1be771
8 changed files with 8 additions and 436 deletions
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68
compiler/rustc_hir_typeck/src/coercion.rs
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@ -41,8 +41,8 @@ use rustc_abi::ExternAbi;
use rustc_attr_parsing::InlineAttr;
use rustc_errors::codes::*;
use rustc_errors::{Applicability, Diag, struct_span_code_err};
use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{self as hir, LangItem};
use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
use rustc_infer::infer::relate::RelateResult;
use rustc_infer::infer::{Coercion, DefineOpaqueTypes, InferOk, InferResult};
@ -55,7 +55,7 @@ use rustc_middle::ty::adjustment::{
Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability, PointerCoercion,
};
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::{self, AliasTy, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Span};
use rustc_trait_selection::infer::InferCtxtExt as _;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
@ -592,63 +592,6 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
// Create an obligation for `Source: CoerceUnsized<Target>`.
let cause = self.cause(self.cause.span, ObligationCauseCode::Coercion { source, target });
let root_obligation = Obligation::new(
self.tcx,
cause.clone(),
self.fcx.param_env,
ty::TraitRef::new(self.tcx, coerce_unsized_did, [coerce_source, coerce_target]),
);
// If the root `Source: CoerceUnsized<Target>` obligation can't possibly hold,
// we don't have to assume that this is unsizing coercion (it will always lead to an error)
//
// However, we don't want to bail early all the time, since the unholdable obligations
// may be interesting for diagnostics (such as trying to coerce `&T` to `&dyn Id<This = U>`),
// so we only bail if there (likely) is another way to convert the types.
if !self.infcx.predicate_may_hold(&root_obligation) {
if let Some(dyn_metadata_adt_def_id) = self.tcx.lang_items().get(LangItem::DynMetadata)
&& let Some(metadata_type_def_id) = self.tcx.lang_items().get(LangItem::Metadata)
{
self.probe(|_| {
let ocx = ObligationCtxt::new(&self.infcx);
// returns `true` if `<ty as Pointee>::Metadata` is `DynMetadata<_>`
let has_dyn_trait_metadata = |ty| {
let metadata_ty: Result<_, _> = ocx.structurally_normalize_ty(
&ObligationCause::dummy(),
self.fcx.param_env,
Ty::new_alias(
self.tcx,
ty::AliasTyKind::Projection,
AliasTy::new(self.tcx, metadata_type_def_id, [ty]),
),
);
metadata_ty.is_ok_and(|metadata_ty| {
metadata_ty
.ty_adt_def()
.is_some_and(|d| d.did() == dyn_metadata_adt_def_id)
})
};
// If both types are raw pointers to a (wrapper over a) trait object,
// this might be a cast like `*const W<dyn Trait> -> *const dyn Trait`.
// So it's better to bail and try that. (even if the cast is not possible, for
// example due to vtables not matching, cast diagnostic will likely still be better)
//
// N.B. use `target`, not `coerce_target` (the latter is a var)
if let &ty::RawPtr(source_pointee, _) = coerce_source.kind()
&& let &ty::RawPtr(target_pointee, _) = target.kind()
&& has_dyn_trait_metadata(source_pointee)
&& has_dyn_trait_metadata(target_pointee)
{
return Err(TypeError::Mismatch);
}
Ok(())
})?;
}
}
// Use a FIFO queue for this custom fulfillment procedure.
//
@ -657,7 +600,12 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
// and almost never more than 3. By using a SmallVec we avoid an
// allocation, at the (very small) cost of (occasionally) having to
// shift subsequent elements down when removing the front element.
let mut queue: SmallVec<[PredicateObligation<'tcx>; 4]> = smallvec![root_obligation];
let mut queue: SmallVec<[PredicateObligation<'tcx>; 4]> = smallvec![Obligation::new(
self.tcx,
cause,
self.fcx.param_env,
ty::TraitRef::new(self.tcx, coerce_unsized_did, [coerce_source, coerce_target])
)];
// Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
// emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where