Fix incorrect usage of `EvaluatedToOk` when evaluating `TypeOutlives`

A global predicate is not guarnatenteed to outlive all regions.
If the predicate involves late-bound regions, then it may fail
to outlive other regions (e.g. `for<'b> &'b bool: 'static` does not
hold)

We now only produce `EvaluatedToOk` when a global predicate has no
late-bound regions - in that case, the ony region that can be present
in the type is 'static

4 files changed, 82 insertions, 1 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 767cb1618bb..ee16d6b3cfb 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -558,7 +558,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 },
 
                 ty::PredicateKind::TypeOutlives(pred) => {
-                    if pred.0.is_known_global() {
+                    // A global type with no late-bound regions can only
+                    // contain the "'static" lifetime (any other lifetime
+                    // would either be late-bound or local), so it is guaranteed
+                    // to outlive any other lifetime
+                    if pred.0.is_global(self.infcx.tcx) && !pred.0.has_late_bound_regions() {
                         Ok(EvaluatedToOk)
                     } else {
                         Ok(EvaluatedToOkModuloRegions)
diff --git a/src/test/ui/traits/project-modulo-regions.rs b/src/test/ui/traits/project-modulo-regions.rs
new file mode 100644
index 00000000000..f0c0dd3ed95
--- /dev/null
+++ b/src/test/ui/traits/project-modulo-regions.rs
@@ -0,0 +1,55 @@
+// revisions: with_clause without_clause
+// Tests that `EvaluatedToOkModuloRegions` from a projection sub-obligation
+// is correctly propagated
+
+#![feature(rustc_attrs)]
+
+trait MyTrait {
+    type Assoc;
+}
+
+struct MyStruct;
+
+impl MyTrait for MyStruct {
+    // Evaluating this projection will result in `EvaluatedToOkModuloRegions`
+    // (when `with_clause` is enabled)
+    type Assoc = <Bar as MyTrait>::Assoc;
+}
+
+struct Bar;
+
+// The `where` clause on this impl will cause us to produce `EvaluatedToOkModuloRegions`
+// when evaluating a projection involving this impl
+#[cfg(with_clause)]
+impl MyTrait for Bar where for<'b> &'b (): 'b {
+    type Assoc = bool;
+}
+
+// This impl tests that the `EvaluatedToOkModuoRegions` result that we get
+// is really due to the `where` clause on the `with_clause` impl
+#[cfg(without_clause)]
+impl MyTrait for Bar {
+    type Assoc = bool;
+}
+
+// The implementation of `#[rustc_evaluate_where_clauses]` doesn't perform
+// normalization, so we need to place the projection predicate behind a normal
+// trait predicate
+struct Helper {}
+trait HelperTrait {}
+impl HelperTrait for Helper where <MyStruct as MyTrait>::Assoc: Sized {}
+
+// Evaluating this 'where' clause will (recursively) end up evaluating
+// `for<'b> &'b (): 'b`, which will produce `EvaluatedToOkModuloRegions`
+#[rustc_evaluate_where_clauses]
+fn test(val: MyStruct) where Helper: HelperTrait  {
+    panic!()
+}
+
+fn foo(val: MyStruct) {
+    test(val);
+    //[with_clause]~^     ERROR evaluate(Binder(TraitPredicate(<Helper as HelperTrait>, polarity:Positive), [])) = Ok(EvaluatedToOkModuloRegions)
+    //[without_clause]~^^ ERROR evaluate(Binder(TraitPredicate(<Helper as HelperTrait>, polarity:Positive), [])) = Ok(EvaluatedToOk)
+}
+
+fn main() {}
diff --git a/src/test/ui/traits/project-modulo-regions.with_clause.stderr b/src/test/ui/traits/project-modulo-regions.with_clause.stderr
new file mode 100644
index 00000000000..2434c32c818
--- /dev/null
+++ b/src/test/ui/traits/project-modulo-regions.with_clause.stderr
@@ -0,0 +1,11 @@
+error: evaluate(Binder(TraitPredicate(<Helper as HelperTrait>, polarity:Positive), [])) = Ok(EvaluatedToOkModuloRegions)
+  --> $DIR/project-modulo-regions.rs:50:5
+   |
+LL | fn test(val: MyStruct) where Helper: HelperTrait  {
+   |                                      ----------- predicate
+...
+LL |     test(val);
+   |     ^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/traits/project-modulo-regions.without_clause.stderr b/src/test/ui/traits/project-modulo-regions.without_clause.stderr
new file mode 100644
index 00000000000..9d35690d5f0
--- /dev/null
+++ b/src/test/ui/traits/project-modulo-regions.without_clause.stderr
@@ -0,0 +1,11 @@
+error: evaluate(Binder(TraitPredicate(<Helper as HelperTrait>, polarity:Positive), [])) = Ok(EvaluatedToOk)
+  --> $DIR/project-modulo-regions.rs:50:5
+   |
+LL | fn test(val: MyStruct) where Helper: HelperTrait  {
+   |                                      ----------- predicate
+...
+LL |     test(val);
+   |     ^^^^
+
+error: aborting due to previous error
+