Don't autoderef infinitely on ambiguity

Author: compiler-errors

compiler/rustc_hir_analysis/src/autoderef.rs

@@ -2,6 +2,7 @@ use crate::errors::AutoDerefReachedRecursionLimit;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
 use crate::traits::NormalizeExt;
 use crate::traits::{self, TraitEngine, TraitEngineExt};
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -138,22 +139,42 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
             return None;
         }
 
-        let normalized_ty = self
-            .infcx
-            .at(&cause, self.param_env)
-            .normalize(tcx.mk_projection(tcx.lang_items().deref_target()?, trait_ref.substs));
-        let mut fulfillcx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
-        let normalized_ty =
-            normalized_ty.into_value_registering_obligations(self.infcx, &mut *fulfillcx);
-        let errors = fulfillcx.select_where_possible(&self.infcx);
+        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
+        let normalized_ty = if tcx.trait_solver_next() {
+            let ty_var = self.infcx.next_ty_var(TypeVariableOrigin {
+                span: self.span,
+                kind: TypeVariableOriginKind::NormalizeProjectionType,
+            });
+            fulfill_cx.register_predicate_obligation(
+                self.infcx,
+                traits::Obligation::new(
+                    tcx,
+                    cause.clone(),
+                    self.param_env,
+                    ty::Binder::dummy(ty::ProjectionPredicate {
+                        projection_ty: tcx.mk_alias_ty(tcx.lang_items().deref_target()?, [ty]),
+                        term: ty_var.into(),
+                    }),
+                ),
+            );
+            ty_var
+        } else {
+            let normalized_ty = self
+                .infcx
+                .at(&cause, self.param_env)
+                .normalize(tcx.mk_projection(tcx.lang_items().deref_target()?, trait_ref.substs));
+            normalized_ty.into_value_registering_obligations(self.infcx, &mut *fulfill_cx)
+        };
+
+        let errors = fulfill_cx.select_where_possible(&self.infcx);
         if !errors.is_empty() {
             // This shouldn't happen, except for evaluate/fulfill mismatches,
             // but that's not a reason for an ICE (`predicate_may_hold` is conservative
             // by design).
             debug!("overloaded_deref_ty: encountered errors {:?} while fulfilling", errors);
             return None;
         }
-        let obligations = fulfillcx.pending_obligations();
+        let obligations = fulfill_cx.pending_obligations();
         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
         self.state.obligations.extend(obligations);
 

tests/ui/traits/new-solver/autoderef-infinite.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Ztrait-solver=next
+
+fn main() {
+    let y = [Default::default()];
+    y[0].method();
+    //~^ ERROR type annotations needed
+    //~| ERROR no method named `method` found
+}

tests/ui/traits/new-solver/autoderef-infinite.stderr

@@ -0,0 +1,16 @@
+error[E0282]: type annotations needed
+  --> $DIR/autoderef-infinite.rs:5:10
+   |
+LL |     y[0].method();
+   |          ^^^^^^ cannot infer type
+
+error[E0599]: no method named `method` found for associated type `<usize as SliceIndex<[_]>>::Output` in the current scope
+  --> $DIR/autoderef-infinite.rs:5:10
+   |
+LL |     y[0].method();
+   |          ^^^^^^ method not found in `<usize as SliceIndex<[_]>>::Output`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0282, E0599.
+For more information about an error, try `rustc --explain E0282`.

tests/ui/traits/new-solver/equating-projection-cyclically.stderr

@@ -1,23 +1,3 @@
-error[E0055]: reached the recursion limit while auto-dereferencing `<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<_ as Test>::Assoc as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target`
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`equating_projection_cyclically`)
-
-error[E0055]: reached the recursion limit while auto-dereferencing `<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<_ as Test>::Assoc as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target`
-  --> $DIR/equating-projection-cyclically.rs:22:9
-   |
-LL |     x = transform(x);
-   |         ^^^^^^^^^^^^ deref recursion limit reached
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`equating_projection_cyclically`)
-
-error[E0055]: reached the recursion limit while auto-dereferencing `<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<_ as Test>::Assoc as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target as Deref>::Target`
-  --> $DIR/equating-projection-cyclically.rs:22:9
-   |
-LL |     x = transform(x);
-   |         ^^^^^^^^^^^^ deref recursion limit reached
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`equating_projection_cyclically`)
-
 error[E0308]: mismatched types
   --> $DIR/equating-projection-cyclically.rs:22:9
    |
@@ -26,7 +6,6 @@ LL |     x = transform(x);
    |         |
    |         cyclic type of infinite size
 
-error: aborting due to 4 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0055, E0308.
-For more information about an error, try `rustc --explain E0055`.
+For more information about this error, try `rustc --explain E0308`.