don't resolve type variables twice

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -347,31 +347,31 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         let obligation = &mut pending_obligation.obligation;
 
         debug!(?obligation, "process_obligation pre-resolve");
+        let infcx = self.selcx.infcx();
 
         if obligation.predicate.has_infer_types_or_consts() {
+            if obligation.predicate.has_late_bound_vars_in_projection() {
+                let mut obligations = Vec::new();
+                let predicate = crate::traits::project::try_normalize_with_depth_to(
+                    self.selcx,
+                    obligation.param_env,
+                    obligation.cause.clone(),
+                    obligation.recursion_depth + 1,
+                    obligation.predicate,
+                    &mut obligations,
+                );
+                if predicate != obligation.predicate {
+                    obligations.push(obligation.with(predicate));
+                    return ProcessResult::Changed(mk_pending(obligations));
+                }
+            }
+
             obligation.predicate =
                 self.selcx.infcx().resolve_vars_if_possible(obligation.predicate);
         }
 
         debug!(?obligation, ?obligation.cause, "process_obligation");
 
-        let infcx = self.selcx.infcx();
-
-        if obligation.predicate.has_late_bound_vars_in_projection() {
-            let mut obligations = Vec::new();
-            let predicate = crate::traits::project::try_normalize_with_depth_to(
-                self.selcx,
-                obligation.param_env,
-                obligation.cause.clone(),
-                obligation.recursion_depth + 1,
-                obligation.predicate,
-                &mut obligations,
-            );
-            if predicate != obligation.predicate {
-                obligations.push(obligation.with(predicate));
-                return ProcessResult::Changed(mk_pending(obligations));
-            }
-        }
         let binder = obligation.predicate.kind();
         match binder.no_bound_vars() {
             None => match binder.skip_binder() {

src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-85455.rs

@@ -7,7 +7,6 @@ trait SomeTrait<'a> {
 fn give_me_ice<T>() {
     callee::<fn(&()) -> <T as SomeTrait<'_>>::Associated>();
     //~^ ERROR the trait bound `T: SomeTrait<'_>` is not satisfied [E0277]
-    //~| ERROR the trait bound `T: SomeTrait<'_>` is not satisfied [E0277]
 }
 
 fn callee<T: Fn<(&'static (),)>>() {

src/test/ui/higher-rank-trait-bounds/normalize-under-binder/issue-85455.stderr

@@ -9,17 +9,6 @@ help: consider restricting type parameter `T`
 LL | fn give_me_ice<T: SomeTrait<'_>>() {
    |                 +++++++++++++++
 
-error[E0277]: the trait bound `T: SomeTrait<'_>` is not satisfied
-  --> $DIR/issue-85455.rs:8:14
-   |
-LL |     callee::<fn(&()) -> <T as SomeTrait<'_>>::Associated>();
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `SomeTrait<'_>` is not implemented for `T`
-   |
-help: consider restricting type parameter `T`
-   |
-LL | fn give_me_ice<T: SomeTrait<'_>>() {
-   |                 +++++++++++++++
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/hrtb/issue-62203-hrtb-ice.stderr

@@ -1,27 +1,3 @@
-error[E0271]: type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39]> as T0<'r, (&'r u8,)>>::O == <_ as Ty<'r>>::V`
-  --> $DIR/issue-62203-hrtb-ice.rs:38:19
-   |
-LL |     let v = Unit2.m(
-   |                   ^ type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39]> as T0<'r, (&'r u8,)>>::O == <_ as Ty<'r>>::V`
-   |
-note: expected this to be `<_ as Ty<'_>>::V`
-  --> $DIR/issue-62203-hrtb-ice.rs:21:14
-   |
-LL |     type O = T::Output;
-   |              ^^^^^^^^^
-   = note: expected associated type `<_ as Ty<'_>>::V`
-                       found struct `Unit4`
-   = help: consider constraining the associated type `<_ as Ty<'_>>::V` to `Unit4` or calling a method that returns `<_ as Ty<'_>>::V`
-   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
-note: required by a bound in `T1::m`
-  --> $DIR/issue-62203-hrtb-ice.rs:27:51
-   |
-LL |     fn m<'a, B: Ty<'a>, F>(&self, f: F) -> Unit1
-   |        - required by a bound in this
-LL |     where
-LL |         F: for<'r> T0<'r, (<Self as Ty<'r>>::V,), O = <B as Ty<'r>>::V>,
-   |                                                   ^^^^^^^^^^^^^^^^^^^^ required by this bound in `T1::m`
-
 error[E0271]: type mismatch resolving `for<'r> <[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39] as FnOnce<((&'r u8,),)>>::Output == Unit3`
   --> $DIR/issue-62203-hrtb-ice.rs:40:9
    |
@@ -48,6 +24,30 @@ LL |     where
 LL |         F: for<'r> T0<'r, (<Self as Ty<'r>>::V,), O = <B as Ty<'r>>::V>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `T1::m`
 
+error[E0271]: type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39]> as T0<'r, (&'r u8,)>>::O == <_ as Ty<'r>>::V`
+  --> $DIR/issue-62203-hrtb-ice.rs:38:19
+   |
+LL |     let v = Unit2.m(
+   |                   ^ type mismatch resolving `for<'r> <L<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39]> as T0<'r, (&'r u8,)>>::O == <_ as Ty<'r>>::V`
+   |
+note: expected this to be `<_ as Ty<'_>>::V`
+  --> $DIR/issue-62203-hrtb-ice.rs:21:14
+   |
+LL |     type O = T::Output;
+   |              ^^^^^^^^^
+   = note: expected associated type `<_ as Ty<'_>>::V`
+                       found struct `Unit4`
+   = help: consider constraining the associated type `<_ as Ty<'_>>::V` to `Unit4` or calling a method that returns `<_ as Ty<'_>>::V`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+note: required by a bound in `T1::m`
+  --> $DIR/issue-62203-hrtb-ice.rs:27:51
+   |
+LL |     fn m<'a, B: Ty<'a>, F>(&self, f: F) -> Unit1
+   |        - required by a bound in this
+LL |     where
+LL |         F: for<'r> T0<'r, (<Self as Ty<'r>>::V,), O = <B as Ty<'r>>::V>,
+   |                                                   ^^^^^^^^^^^^^^^^^^^^ required by this bound in `T1::m`
+
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0271`.