Change inference var check to be in project_type

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -2470,7 +2470,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let projection_ty = ty::ProjectionTy {
                     // `T`
                     substs: self.tcx.mk_substs_trait(
-                        trait_ref.self_ty().skip_binder(),
+                        trait_pred.self_ty().skip_binder(),
                         &self.fresh_substs_for_item(span, item_def_id)[1..],
                     ),
                     // `Future::Output`

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1073,6 +1073,16 @@ fn project<'cx, 'tcx>(
         return Ok(Projected::Progress(Progress::error(selcx.tcx())));
     }
 
+    // If the obligation contains any inference types or consts in associated
+    // type substs, then we don't assemble any candidates.
+    // This isn't really correct, but otherwise we can end up in a case where
+    // we constrain inference variables by selecting a single predicate, when
+    // we need to stay general. See issue #91762.
+    let (_, predicate_own_substs) = obligation.predicate.trait_ref_and_own_substs(selcx.tcx());
+    if predicate_own_substs.iter().any(|g| g.has_infer_types_or_consts()) {
+        return Err(ProjectionError::TooManyCandidates);
+    }
+
     let mut candidates = ProjectionCandidateSet::None;
 
     // Make sure that the following procedures are kept in order. ParamEnv

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1521,16 +1521,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             infer_predicate.projection_ty
         };
 
-        // If the obligation contains any inference types or consts in associated
-        // type substs, then we don't match any projection candidates against it.
-        // This isn't really correct, but otherwise we can end up in a case where
-        // we constrain inference variables by selecting a single predicate, when
-        // we need to stay general. See issue #91762.
-        let (_, predicate_own_substs) =
-            obligation.predicate.trait_ref_and_own_substs(self.infcx.tcx);
-        if predicate_own_substs.iter().any(|g| g.has_infer_types_or_consts()) {
-            return false;
-        }
         self.infcx
             .at(&obligation.cause, obligation.param_env)
             .sup(obligation.predicate, infer_projection)

src/test/ui/generic-associated-types/issue-74824.rs

@@ -17,6 +17,7 @@ impl<T> UnsafeCopy for T {}
 fn main() {
     let b = Box::new(42usize);
     let copy = <()>::copy(&b);
+    //~^ type annotations needed
 
     let raw_b = Box::deref(&b) as *const _;
     let raw_copy = Box::deref(&copy) as *const _;

src/test/ui/generic-associated-types/issue-74824.stderr

@@ -27,6 +27,13 @@ help: consider restricting type parameter `T`
 LL |     type Copy<T: std::clone::Clone>: Copy = Box<T>;
    |                +++++++++++++++++++
 
-error: aborting due to 2 previous errors
+error[E0282]: type annotations needed
+  --> $DIR/issue-74824.rs:19:16
+   |
+LL |     let copy = <()>::copy(&b);
+   |                ^^^^^^^^^^ cannot infer type for type parameter `T` declared on the associated function `copy`
+
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0277, E0282.
+For more information about an error, try `rustc --explain E0277`.

src/test/ui/generic-associated-types/issue-91762.rs

@@ -23,7 +23,7 @@ pub trait FunctorExt<T>: Sized {
 
         arg = self;
         ret = <Self::Base as Functor>::fmap(arg);
-        //~^ mismatched types
+        //~^ type annotations needed
     }
 }
 

src/test/ui/generic-associated-types/issue-91762.stderr

@@ -1,22 +1,9 @@
-error[E0308]: mismatched types
-  --> $DIR/issue-91762.rs:25:45
+error[E0282]: type annotations needed
+  --> $DIR/issue-91762.rs:25:15
    |
-LL | / pub trait FunctorExt<T>: Sized {
-LL | |     type Base: Functor<With<T> = Self>;
-LL | |
-LL | |     fn fmap<U>(self) {
-...  |
-LL | |         ret = <Self::Base as Functor>::fmap(arg);
-   | |                                             ^^^ expected associated type, found type parameter `Self`
-LL | |
-LL | |     }
-LL | | }
-   | |_- this type parameter
-   |
-   = note: expected associated type `<<Self as FunctorExt<T>>::Base as Functor>::With<_>`
-               found type parameter `Self`
-   = note: you might be missing a type parameter or trait bound
+LL |         ret = <Self::Base as Functor>::fmap(arg);
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the associated function `fmap`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0282`.