coolio

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

@@ -419,7 +419,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     let mut no_candidates_apply = true;
 
                     for c in candidate_set.vec.iter() {
-                        if self.evaluate_candidate(stack, c)?.may_apply() {
+                        if self.evaluate_candidate(stack, c, false)?.may_apply() {
                             no_candidates_apply = false;
                             break;
                         }
@@ -490,7 +490,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // is needed for specialization. Propagate overflow if it occurs.
         let mut candidates = candidates
             .into_iter()
-            .map(|c| match self.evaluate_candidate(stack, &c) {
+            .map(|c| match self.evaluate_candidate(stack, &c, false) {
                 Ok(eval) if eval.may_apply() => {
                     Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
                 }
@@ -1234,7 +1234,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
 
         match self.candidate_from_obligation(stack) {
-            Ok(Some(c)) => self.evaluate_candidate(stack, &c),
+            Ok(Some(c)) => self.evaluate_candidate(stack, &c, true),
             Ok(None) => Ok(EvaluatedToAmbig),
             Err(Overflow(OverflowError::Canonical)) => Err(OverflowError::Canonical),
             Err(..) => Ok(EvaluatedToErr),
@@ -1269,6 +1269,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
         candidate: &SelectionCandidate<'tcx>,
+        leak_check_higher_ranked_goal: bool,
     ) -> Result<EvaluationResult, OverflowError> {
         let mut result = self.evaluation_probe(|this, outer_universe| {
             // We eagerly instantiate higher ranked goals to prevent universe errors
@@ -1281,7 +1282,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // in an overlap error in coherence.
             let p = self.infcx.instantiate_binder_with_placeholders(stack.obligation.predicate);
             let obligation = stack.obligation.with(this.tcx(), ty::Binder::dummy(p));
-            *outer_universe = self.infcx.universe();
+            if !leak_check_higher_ranked_goal {
+                *outer_universe = self.infcx.universe();
+            }
             match this.confirm_candidate(&obligation, candidate.clone()) {
                 Ok(selection) => {
                     debug!(?selection);

tests/ui/higher-ranked/trait-bounds/issue-30786-1.rs

@@ -1,6 +1,6 @@
 // normalize-stderr-test: "long-type-\d+" -> "long-type-hash"
 
-// rust-lang/rust#30786: the use of `for<'b> &'b mut A: Stream<Item=T`
+// rust-lang/rust#30786: the use of `for<'b> &'b mut A: Stream<Item=T>`
 // should act as assertion that item does not borrow from its stream;
 // but an earlier buggy rustc allowed `.map(|x: &_| x)` which does
 // have such an item.
@@ -113,12 +113,8 @@ fn variant1() {
     // we deduce it somehow from a reuqirement that `Map: Stream` I
     // guess.
     let map = source.mapx(|x: &_| x);
-    //~^ ERROR implementation of `FnOnce` is not general enough
     let filter = map.filterx(|x: &_| true);
-    //~^ ERROR implementation of `FnOnce` is not general enough
-    //~| ERROR implementation of `FnOnce` is not general enough
-    //~| ERROR implementation of `FnOnce` is not general enough
-    //~| ERROR implementation of `FnOnce` is not general enough
+    //~^ ERROR the method `filterx` exists for struct
 }
 
 fn main() {}

tests/ui/higher-ranked/trait-bounds/issue-30786-1.stderr

@@ -1,50 +1,21 @@
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-30786-1.rs:115:15
-   |
-LL |     let map = source.mapx(|x: &_| x);
-   |               ^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
-   |
-   = note: closure with signature `fn(&'2 u64) -> &u64` must implement `FnOnce<(&'1 u64,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 u64,)>`, for some specific lifetime `'2`
-
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-30786-1.rs:117:18
-   |
-LL |     let filter = map.filterx(|x: &_| true);
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
-   |
-   = note: closure with signature `fn(&'2 u64) -> &u64` must implement `FnOnce<(&'1 u64,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 u64,)>`, for some specific lifetime `'2`
-
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-30786-1.rs:117:18
+error[E0599]: the method `filterx` exists for struct `Map<Repeat, {closure@issue-30786-1.rs:115:27}>`, but its trait bounds were not satisfied
+  --> $DIR/issue-30786-1.rs:116:22
    |
+LL | pub struct Map<S, F> {
+   | -------------------- method `filterx` not found for this struct because it doesn't satisfy `_: StreamExt`
+...
 LL |     let filter = map.filterx(|x: &_| true);
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
+   |                      ^^^^^^^ method cannot be called on `Map<Repeat, {closure@issue-30786-1.rs:115:27}>` due to unsatisfied trait bounds
    |
-   = note: closure with signature `fn(&'2 u64) -> &u64` must implement `FnOnce<(&'1 u64,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 u64,)>`, for some specific lifetime `'2`
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-30786-1.rs:117:18
-   |
-LL |     let filter = map.filterx(|x: &_| true);
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
-   |
-   = note: closure with signature `fn(&'2 u64) -> &u64` must implement `FnOnce<(&'1 u64,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 u64,)>`, for some specific lifetime `'2`
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: implementation of `FnOnce` is not general enough
-  --> $DIR/issue-30786-1.rs:117:18
-   |
-LL |     let filter = map.filterx(|x: &_| true);
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
+note: the following trait bounds were not satisfied:
+      `&'a mut &Map<Repeat, {closure@$DIR/issue-30786-1.rs:115:27: 115:34}>: Stream`
+      `&'a mut &mut Map<Repeat, {closure@$DIR/issue-30786-1.rs:115:27: 115:34}>: Stream`
+      `&'a mut Map<Repeat, {closure@$DIR/issue-30786-1.rs:115:27: 115:34}>: Stream`
+  --> $DIR/issue-30786-1.rs:98:50
    |
-   = note: closure with signature `fn(&'2 u64) -> &u64` must implement `FnOnce<(&'1 u64,)>`, for any lifetime `'1`...
-   = note: ...but it actually implements `FnOnce<(&'2 u64,)>`, for some specific lifetime `'2`
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+LL | impl<T> StreamExt for T where for<'a> &'a mut T: Stream {}
+   |         ---------     -                          ^^^^^^ unsatisfied trait bound introduced here
 
-error: aborting due to 5 previous errors
+error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0599`.