Correctly handle binders inside trait predicates

src/librustc_resolve/late/lifetimes.rs

@@ -883,7 +883,6 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                         })
                         .collect();
                     if !lifetimes.is_empty() {
-                        self.trait_ref_hack = true;
                         let next_early_index = self.next_early_index();
                         let scope = Scope::Binder {
                             lifetimes,
@@ -895,9 +894,10 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                         let result = self.with(scope, |old_scope, this| {
                             this.check_lifetime_params(old_scope, &bound_generic_params);
                             this.visit_ty(&bounded_ty);
+                            this.trait_ref_hack = true;
                             walk_list!(this, visit_param_bound, bounds);
+                            this.trait_ref_hack = false;
                         });
-                        self.trait_ref_hack = false;
                         result
                     } else {
                         self.visit_ty(&bounded_ty);
@@ -932,13 +932,15 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
         debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
 
         let should_pop_missing_lt = self.is_trait_ref_fn_scope(trait_ref);
-        if !self.trait_ref_hack
+
+        let trait_ref_hack = take(&mut self.trait_ref_hack);
+        if !trait_ref_hack
             || trait_ref.bound_generic_params.iter().any(|param| match param.kind {
                 GenericParamKind::Lifetime { .. } => true,
                 _ => false,
             })
         {
-            if self.trait_ref_hack {
+            if trait_ref_hack {
                 struct_span_err!(
                     self.tcx.sess,
                     trait_ref.span,
@@ -968,10 +970,11 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
                 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
                 this.visit_trait_ref(&trait_ref.trait_ref);
-            })
+            });
         } else {
             self.visit_trait_ref(&trait_ref.trait_ref);
         }
+        self.trait_ref_hack = trait_ref_hack;
         if should_pop_missing_lt {
             self.missing_named_lifetime_spots.pop();
         }

src/test/ui/where-clauses/where-lifetime-resolution.rs

@@ -7,7 +7,6 @@ fn f() where
     //~^ ERROR use of undeclared lifetime name `'a`
     for<'a> dyn for<'b> Trait2<'a, 'b>: Trait2<'a, 'b>,
     //~^ ERROR use of undeclared lifetime name `'b`
-    //~| ERROR nested quantification of lifetimes
 {}
 
 fn main() {}

src/test/ui/where-clauses/where-lifetime-resolution.stderr

@@ -7,12 +7,6 @@ LL |     for<'a> dyn Trait1<'a>: Trait1<'a>, // OK
 LL |     (dyn for<'a> Trait1<'a>): Trait1<'a>,
    |                                      ^^ undeclared lifetime
 
-error[E0316]: nested quantification of lifetimes
-  --> $DIR/where-lifetime-resolution.rs:8:17
-   |
-LL |     for<'a> dyn for<'b> Trait2<'a, 'b>: Trait2<'a, 'b>,
-   |                 ^^^^^^^^^^^^^^^^^^^^^^
-
 error[E0261]: use of undeclared lifetime name `'b`
   --> $DIR/where-lifetime-resolution.rs:8:52
    |
@@ -22,6 +16,6 @@ LL | fn f() where
 LL |     for<'a> dyn for<'b> Trait2<'a, 'b>: Trait2<'a, 'b>,
    |                                                    ^^ undeclared lifetime
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0261`.