Revert to only using opportunistic_resolve_vars for existing places

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -322,7 +322,22 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
                 }
             }
 
-            ty::ReVar(_) => self.canonicalize_region_mode.canonicalize_free_region(self, r),
+            ty::ReVar(vid) => {
+                let resolved_vid = self
+                    .infcx
+                    .unwrap()
+                    .inner
+                    .borrow_mut()
+                    .unwrap_region_constraints()
+                    .opportunistic_resolve_var(vid);
+                debug!(
+                    "canonical: region var found with vid {:?}, \
+                     opportunistically resolved to {:?}",
+                    vid, r
+                );
+                let r = self.tcx.reuse_or_mk_region(r, ty::ReVar(resolved_vid));
+                self.canonicalize_region_mode.canonicalize_free_region(self, r)
+            }
 
             ty::ReStatic
             | ty::ReEarlyBound(..)

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -623,6 +623,10 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         }
     }
 
+    pub fn opportunistic_resolve_var(&mut self, rid: ty::RegionVid) -> ty::RegionVid {
+        self.unification_table().find(rid).vid
+    }
+
     pub fn opportunistic_resolve_region(
         &mut self,
         tcx: TyCtxt<'tcx>,
@@ -692,8 +696,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         &self,
         value_count: usize,
     ) -> (Range<RegionVid>, Vec<RegionVariableOrigin>) {
-        let range = RegionVid::from(value_count as u32)
+        let range = RegionVid::from(value_count)..RegionVid::from(self.unification_table.len());
-            ..RegionVid::from(self.unification_table.len() as u32);
         (
             range.clone(),
             (range.start.index()..range.end.index())

compiler/rustc_infer/src/infer/resolve.rs

@@ -84,12 +84,18 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticRegionResolver<'a, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        let tcx = self.tcx();
+        match *r {
-        self.infcx
+            ty::ReVar(rid) => {
+                let resolved = self
+                    .infcx
                     .inner
                     .borrow_mut()
                     .unwrap_region_constraints()
-            .opportunistic_resolve_region(tcx, r)
+                    .opportunistic_resolve_var(rid);
+                self.tcx().reuse_or_mk_region(r, ty::ReVar(resolved))
+            }
+            _ => r,
+        }
     }
 
     fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {

src/test/ui/associated-types/associated-types-eq-hr.rs

@@ -102,8 +102,6 @@ pub fn call_tuple_two() {
     tuple_two::<Tuple>();
     //~^ ERROR implementation of `TheTrait` is not general enough
     //~| ERROR implementation of `TheTrait` is not general enough
-    //~| ERROR mismatched types
-    //~| ERROR mismatched types
 }
 
 pub fn call_tuple_three() {

src/test/ui/associated-types/associated-types-eq-hr.stderr

@@ -46,34 +46,6 @@ LL |     tuple_one::<Tuple>();
    = note: `Tuple` must implement `TheTrait<(&'0 isize, &'1 isize)>`, for any two lifetimes `'0` and `'1`...
    = note: ...but it actually implements `TheTrait<(&'2 isize, &'2 isize)>`, for some specific lifetime `'2`
 
-error[E0308]: mismatched types
-  --> $DIR/associated-types-eq-hr.rs:102:5
-   |
-LL |     tuple_two::<Tuple>();
-   |     ^^^^^^^^^^^^^^^^^^ lifetime mismatch
-   |
-   = note: expected reference `&'x isize`
-              found reference `&'y isize`
-note: the lifetime requirement is introduced here
-  --> $DIR/associated-types-eq-hr.rs:66:53
-   |
-LL |     T: for<'x, 'y> TheTrait<(&'x isize, &'y isize), A = &'y isize>,
-   |                                                     ^^^^^^^^^^^^^
-
-error[E0308]: mismatched types
-  --> $DIR/associated-types-eq-hr.rs:102:5
-   |
-LL |     tuple_two::<Tuple>();
-   |     ^^^^^^^^^^^^^^^^^^ lifetime mismatch
-   |
-   = note: expected reference `&'x isize`
-              found reference `&'y isize`
-note: the lifetime requirement is introduced here
-  --> $DIR/associated-types-eq-hr.rs:66:53
-   |
-LL |     T: for<'x, 'y> TheTrait<(&'x isize, &'y isize), A = &'y isize>,
-   |                                                     ^^^^^^^^^^^^^
-
 error: implementation of `TheTrait` is not general enough
   --> $DIR/associated-types-eq-hr.rs:102:5
    |
@@ -93,7 +65,7 @@ LL |     tuple_two::<Tuple>();
    = note: ...but it actually implements `TheTrait<(&'2 isize, &'2 isize)>`, for some specific lifetime `'2`
 
 error: implementation of `TheTrait` is not general enough
-  --> $DIR/associated-types-eq-hr.rs:114:5
+  --> $DIR/associated-types-eq-hr.rs:112:5
    |
 LL |     tuple_four::<Tuple>();
    |     ^^^^^^^^^^^^^^^^^^^ implementation of `TheTrait` is not general enough
@@ -101,7 +73,6 @@ LL |     tuple_four::<Tuple>();
    = note: `Tuple` must implement `TheTrait<(&'0 isize, &'1 isize)>`, for any two lifetimes `'0` and `'1`...
    = note: ...but it actually implements `TheTrait<(&'2 isize, &'2 isize)>`, for some specific lifetime `'2`
 
-error: aborting due to 9 previous errors
+error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0271, E0308.
+For more information about this error, try `rustc --explain E0271`.
-For more information about an error, try `rustc --explain E0271`.

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

@@ -9,7 +9,7 @@ LL |     let v = Unit2.m(
    = help: consider constraining the associated type `<_ as Ty<'_>>::V` to `Unit4`
    = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
 
-error[E0271]: type mismatch resolving `<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39] as FnOnce<((&'r u8,),)>>::Output == Unit3`
+error[E0271]: type mismatch resolving `<[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:39] as FnOnce<((&u8,),)>>::Output == Unit3`
   --> $DIR/issue-62203-hrtb-ice.rs:38:19
    |
 LL |     let v = Unit2.m(

src/test/ui/rfc1623.rs

@@ -23,10 +23,6 @@ static SOME_STRUCT: &SomeStruct = &SomeStruct {
     bar: &Bar { bools: &[true, true] },
     f: &id,
     //~^ ERROR implementation of `FnOnce` is not general enough
-    //~^^ mismatched types
-    //~^^^ mismatched types
-    //~^^^^ mismatched types
-    //~^^^^^ mismatched types
 };
 
 // very simple test for a 'static static with default lifetime

src/test/ui/rfc1623.stderr

@@ -1,39 +1,3 @@
-error[E0308]: mismatched types
-  --> $DIR/rfc1623.rs:24:8
-   |
-LL |     f: &id,
-   |        ^^^ one type is more general than the other
-   |
-   = note: expected reference `&'a Foo<'b>`
-              found reference `&'a Foo<'b>`
-
-error[E0308]: mismatched types
-  --> $DIR/rfc1623.rs:24:8
-   |
-LL |     f: &id,
-   |        ^^^ one type is more general than the other
-   |
-   = note: expected reference `&'a Foo<'b>`
-              found reference `&'a Foo<'b>`
-
-error[E0308]: mismatched types
-  --> $DIR/rfc1623.rs:24:8
-   |
-LL |     f: &id,
-   |        ^^^ one type is more general than the other
-   |
-   = note: expected reference `&'a Foo<'b>`
-              found reference `&'a Foo<'b>`
-
-error[E0308]: mismatched types
-  --> $DIR/rfc1623.rs:24:8
-   |
-LL |     f: &id,
-   |        ^^^ one type is more general than the other
-   |
-   = note: expected reference `&'a Foo<'b>`
-              found reference `&'a Foo<'b>`
-
 error: implementation of `FnOnce` is not general enough
   --> $DIR/rfc1623.rs:24:8
    |
@@ -43,6 +7,5 @@ LL |     f: &id,
    = note: `fn(&'2 Foo<'_>) -> &'2 Foo<'_> {id::<&'2 Foo<'_>>}` must implement `FnOnce<(&'1 Foo<'b>,)>`, for any lifetime `'1`...
    = note: ...but it actually implements `FnOnce<(&'2 Foo<'_>,)>`, for some specific lifetime `'2`
 
-error: aborting due to 5 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.

src/test/ui/traits/inductive-overflow/lifetime.rs

@@ -26,4 +26,6 @@ fn main() {
     // Should only be a few notes.
     is_send::<X<C<'static>>>();
     //~^ ERROR overflow evaluating
+    //~| 2 redundant requirements hidden
+    //~| required because of
 }

src/test/ui/traits/inductive-overflow/lifetime.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow evaluating the requirement `Box<X<C<'static>>>: NotAuto`
+error[E0275]: overflow evaluating the requirement `Box<X<C<'_>>>: NotAuto`
   --> $DIR/lifetime.rs:27:5
    |
 LL | fn is_send<S: NotAuto>() {}
@@ -7,11 +7,13 @@ LL | fn is_send<S: NotAuto>() {}
 LL |     is_send::<X<C<'static>>>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-note: required because of the requirements on the impl of `NotAuto` for `X<C<'static>>`
+note: required because of the requirements on the impl of `NotAuto` for `X<C<'_>>`
   --> $DIR/lifetime.rs:19:12
    |
 LL | impl<T: Y> NotAuto for X<T> where T::P: NotAuto {}
    |            ^^^^^^^     ^^^^
+   = note: 2 redundant requirements hidden
+   = note: required because of the requirements on the impl of `NotAuto` for `X<C<'static>>`
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/issue-60371.rs

@@ -9,7 +9,7 @@ trait Bug {
 impl Bug for &() {
     type Item = impl Bug; //~ ERROR `impl Trait` in type aliases is unstable
     //~^ ERROR the trait bound `(): Bug` is not satisfied
-    //~^^ ERROR the trait bound
+    //~^^ ERROR could not find defining uses
 
     const FUN: fn() -> Self::Item = || ();
     //~^ ERROR type alias impl trait is not permitted here

src/test/ui/type-alias-impl-trait/issue-60371.stderr

@@ -25,14 +25,11 @@ LL |     type Item = impl Bug;
    = help: the following implementations were found:
              <&() as Bug>
 
-error[E0277]: the trait bound `(): Bug` is not satisfied
+error: could not find defining uses
   --> $DIR/issue-60371.rs:10:17
    |
 LL |     type Item = impl Bug;
-   |                 ^^^^^^^^ the trait `Bug` is not implemented for `()`
+   |                 ^^^^^^^^
-   |
-   = help: the following implementations were found:
-             <&() as Bug>
 
 error: aborting due to 4 previous errors