X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;ds=sidebyside;f=compiler%2Frustc_trait_selection%2Fsrc%2Ftraits%2Fselect%2Fmod.rs;h=8bcb1ccb5846d42586dc3168dac96015641e5b86;hb=02ff9e0aef03d48fdecc2d114311217010ec1d81;hp=64af875dd22bbb8a2024f88e824c79fd90e76dba;hpb=f1c918f1f3166c1cb2624ce2e2783d357e70dc3d;p=rust.git

diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 64af875dd22..8bcb1ccb584 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -29,7 +29,7 @@
 use crate::traits::ProjectionCacheKey;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
-use rustc_errors::ErrorReported;
+use rustc_errors::{Diagnostic, ErrorReported};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::LateBoundRegionConversionTime;
@@ -64,7 +64,7 @@ pub enum IntercrateAmbiguityCause {
 impl IntercrateAmbiguityCause {
     /// Emits notes when the overlap is caused by complex intercrate ambiguities.
     /// See #23980 for details.
-    pub fn add_intercrate_ambiguity_hint(&self, err: &mut rustc_errors::DiagnosticBuilder<'_>) {
+    pub fn add_intercrate_ambiguity_hint(&self, err: &mut Diagnostic) {
         err.note(&self.intercrate_ambiguity_hint());
     }
 
@@ -922,7 +922,7 @@ fn evaluate_stack<'o>(
                         if !candidate_set.ambiguous && candidate_set.vec.is_empty() {
                             let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
                             let self_ty = trait_ref.self_ty();
-                            let cause = with_no_trimmed_paths(|| {
+                            let cause = with_no_trimmed_paths!({
                                 IntercrateAmbiguityCause::DownstreamCrate {
                                     trait_desc: trait_ref.print_only_trait_path().to_string(),
                                     self_desc: if self_ty.has_concrete_skeleton() {
@@ -1481,7 +1481,7 @@ fn match_normalize_trait_ref(
             .map_err(|_| ())
     }
 
-    fn evaluate_where_clause<'o>(
+    fn where_clause_may_apply<'o>(
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
         where_clause_trait_ref: ty::PolyTraitRef<'tcx>,
@@ -1494,12 +1494,18 @@ fn evaluate_where_clause<'o>(
         })
     }
 
+    /// Return `Yes` if the obligation's predicate type applies to the env_predicate, and
+    /// `No` if it does not. Return `Ambiguous` in the case that the projection type is a GAT,
+    /// and applying this env_predicate constrains any of the obligation's GAT substitutions.
+    ///
+    /// This behavior is a somewhat of a hack to prevent overconstraining inference variables
+    /// in cases like #91762.
     pub(super) fn match_projection_projections(
         &mut self,
         obligation: &ProjectionTyObligation<'tcx>,
         env_predicate: PolyProjectionPredicate<'tcx>,
         potentially_unnormalized_candidates: bool,
-    ) -> bool {
+    ) -> ProjectionMatchesProjection {
         let mut nested_obligations = Vec::new();
         let (infer_predicate, _) = self.infcx.replace_bound_vars_with_fresh_vars(
             obligation.cause.span,
@@ -1521,7 +1527,8 @@ pub(super) fn match_projection_projections(
             infer_predicate.projection_ty
         };
 
-        self.infcx
+        let is_match = self
+            .infcx
             .at(&obligation.cause, obligation.param_env)
             .sup(obligation.predicate, infer_projection)
             .map_or(false, |InferOk { obligations, value: () }| {
@@ -1530,7 +1537,26 @@ pub(super) fn match_projection_projections(
                     nested_obligations.into_iter().chain(obligations),
                 )
                 .map_or(false, |res| res.may_apply())
-            })
+            });
+
+        if is_match {
+            let generics = self.tcx().generics_of(obligation.predicate.item_def_id);
+            // FIXME(generic-associated-types): Addresses aggressive inference in #92917.
+            // If this type is a GAT, and of the GAT substs resolve to something new,
+            // that means that we must have newly inferred something about the GAT.
+            // We should give up in that case.
+            if !generics.params.is_empty()
+                && obligation.predicate.substs[generics.parent_count..]
+                    .iter()
+                    .any(|&p| p.has_infer_types_or_consts() && self.infcx.shallow_resolve(p) != p)
+            {
+                ProjectionMatchesProjection::Ambiguous
+            } else {
+                ProjectionMatchesProjection::Yes
+            }
+        } else {
+            ProjectionMatchesProjection::No
+        }
     }
 
     ///////////////////////////////////////////////////////////////////////////
@@ -1826,9 +1852,7 @@ fn sized_conditions(
             ty::Str | ty::Slice(_) | ty::Dynamic(..) | ty::Foreign(..) => None,
 
             ty::Tuple(tys) => Where(
-                obligation
-                    .predicate
-                    .rebind(tys.last().into_iter().map(|k| k.expect_ty()).collect()),
+                obligation.predicate.rebind(tys.last().map_or_else(Vec::new, |&last| vec![last])),
             ),
 
             ty::Adt(def, substs) => {
@@ -1891,7 +1915,7 @@ fn copy_clone_conditions(
 
             ty::Tuple(tys) => {
                 // (*) binder moved here
-                Where(obligation.predicate.rebind(tys.iter().map(|k| k.expect_ty()).collect()))
+                Where(obligation.predicate.rebind(tys.iter().collect()))
             }
 
             ty::Closure(_, substs) => {
@@ -1971,7 +1995,7 @@ fn constituent_types_for_ty(
 
             ty::Tuple(ref tys) => {
                 // (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
-                t.rebind(tys.iter().map(|k| k.expect_ty()).collect())
+                t.rebind(tys.iter().collect())
             }
 
             ty::Closure(_, ref substs) => {
@@ -2709,3 +2733,9 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "TraitObligationStack({:?})", self.obligation)
     }
 }
+
+pub enum ProjectionMatchesProjection {
+    Yes,
+    Ambiguous,
+    No,
+}