bjoernager/rust
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Auto merge of #127172 - compiler-errors:full-can_eq-everywhere, r=lcnr

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Make `can_eq` process obligations (almost) everywhere

Move `can_eq` to an extension trait on `InferCtxt` in `rustc_trait_selection`, and change it so that it processes obligations. This should strengthen it to be more accurate in some cases, but is most important for the new trait solver which delays relating aliases to `AliasRelate` goals. Without this, we always basically just return true when passing aliases to `can_eq`, which can lead to weird errors, for example #127149.

I'm not actually certain if we should *have* `can_eq` be called on the good path. In cases where we need `can_eq`, we probably should just be using a regular probe.

Fixes #127149

r? lcnr
This commit is contained in:
bors 2024-07-07 23:03:48 +00:00
commit 89aefb9c53
30 changed files with 133 additions and 154 deletions
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4
compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
View file

@ -820,7 +820,7 @@ fn foo(&self) -> Self::T { String::new() }
tcx.defaultness(item.id.owner_id)
{
let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
if self.infcx.can_eq(param_env, assoc_ty, found) {
if self.infcx.can_eq_shallow(param_env, assoc_ty, found) {
diag.span_label(
item.span,
"associated type defaults can't be assumed inside the \
@ -843,7 +843,7 @@ fn foo(&self) -> Self::T { String::new() }
let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
if let hir::Defaultness::Default { has_value: true } =
tcx.defaultness(item.id.owner_id)
&& self.infcx.can_eq(param_env, assoc_ty, found)
&& self.infcx.can_eq_shallow(param_env, assoc_ty, found)
{
diag.span_label(
item.span,

16
compiler/rustc_infer/src/infer/mod.rs
View file

@ -768,19 +768,9 @@ impl<'tcx> InferCtxt<'tcx> {
.collect()
}
pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, expected: T, actual: T) -> bool
where
T: at::ToTrace<'tcx>,
{
let origin = &ObligationCause::dummy();
self.probe(|_| {
// We're only answering whether there could be a subtyping relation, and with
// opaque types, "there could be one", via registering a hidden type.
self.at(origin, param_env).sub(DefineOpaqueTypes::Yes, expected, actual).is_ok()
})
}
pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
// FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
// or we need to process the obligations.
pub fn can_eq_shallow<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
where
T: at::ToTrace<'tcx>,
{