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Fix next solver handling of shallow trait impl check

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This commit is contained in:
Oli Scherer 2025-03-17 08:16:52 +00:00
parent 055d31c7a5
commit 14cd467001
5 changed files with 57 additions and 14 deletions
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30
compiler/rustc_trait_selection/src/infer.rs
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@ -15,7 +15,7 @@ use tracing::instrument;
use crate::infer::at::ToTrace;
use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
use crate::traits::{self, Obligation, ObligationCause, ObligationCtxt, SelectionContext};
use crate::traits::{self, Obligation, ObligationCause, ObligationCtxt};
#[extension(pub trait InferCtxtExt<'tcx>)]
impl<'tcx> InferCtxt<'tcx> {
@ -122,9 +122,6 @@ impl<'tcx> InferCtxt<'tcx> {
/// - If this returns `Some([errors..])`, then the trait has an impl for
/// the self type, but some nested obligations do not hold.
/// - If this returns `None`, no implementation that applies could be found.
///
/// FIXME(-Znext-solver): Due to the recursive nature of the new solver,
/// this will probably only ever return `Some([])` or `None`.
fn type_implements_trait_shallow(
&self,
trait_def_id: DefId,
@ -132,20 +129,29 @@ impl<'tcx> InferCtxt<'tcx> {
param_env: ty::ParamEnv<'tcx>,
) -> Option<Vec<traits::FulfillmentError<'tcx>>> {
self.probe(|_snapshot| {
let mut selcx = SelectionContext::new(self);
match selcx.select(&Obligation::new(
let ocx = ObligationCtxt::new_with_diagnostics(self);
ocx.register_obligation(Obligation::new(
self.tcx,
ObligationCause::dummy(),
param_env,
ty::TraitRef::new(self.tcx, trait_def_id, [ty]),
)) {
Ok(Some(selection)) => {
let ocx = ObligationCtxt::new_with_diagnostics(self);
ocx.register_obligations(selection.nested_obligations());
Some(ocx.select_all_or_error())
));
let errors = ocx.select_where_possible();
// Find the original predicate in the list of predicates that could definitely not be fulfilled.
// If it is in that list, then we know this doesn't even shallowly implement the trait.
// If it is not in that list, it was fulfilled, but there may be nested obligations, which we don't care about here.
for error in &errors {
let Some(trait_clause) = error.obligation.predicate.as_trait_clause() else {
continue;
};
let Some(bound_ty) = trait_clause.self_ty().no_bound_vars() else { continue };
if trait_clause.def_id() == trait_def_id
&& ocx.eq(&ObligationCause::dummy(), param_env, bound_ty, ty).is_ok()
{
return None;
}
Ok(None) | Err(_) => None,
}
Some(errors)
})
}
}