normalize_erasing_regions -> try_normalize_erasing_regions

Author: smoelius

tests/ui/needless_borrow.fixed

@@ -139,6 +139,7 @@ fn main() {
     let _ = std::any::Any::type_id(&""); // Don't lint. `Any` is only bound
     let _ = Box::new(&""); // Don't lint. Type parameter appears in return type
     ref_as_ref_path(&""); // Don't lint. Argument type is not a type parameter
+    refs_only(&()); // Don't lint. `&T` implements trait, but `T` doesn't
     multiple_constraints_normalizes_to_different(&[[""]], &[""]); // Don't lint. Projected type appears in arguments
 }
 
@@ -238,6 +239,20 @@ where
 {
 }
 
+trait RefsOnly {
+    type Referent;
+}
+
+impl<T> RefsOnly for &T {
+    type Referent = T;
+}
+
+fn refs_only<T>(_: T)
+where
+    T: RefsOnly<Referent = ()>,
+{
+}
+
 fn multiple_constraints_normalizes_to_different<T, U, V>(_: T, _: U)
 where
     T: IntoIterator<Item = U>,

tests/ui/needless_borrow.rs

@@ -139,6 +139,7 @@ fn main() {
     let _ = std::any::Any::type_id(&""); // Don't lint. `Any` is only bound
     let _ = Box::new(&""); // Don't lint. Type parameter appears in return type
     ref_as_ref_path(&""); // Don't lint. Argument type is not a type parameter
+    refs_only(&()); // Don't lint. `&T` implements trait, but `T` doesn't
     multiple_constraints_normalizes_to_different(&[[""]], &[""]); // Don't lint. Projected type appears in arguments
 }
 
@@ -238,6 +239,20 @@ where
 {
 }
 
+trait RefsOnly {
+    type Referent;
+}
+
+impl<T> RefsOnly for &T {
+    type Referent = T;
+}
+
+fn refs_only<T>(_: T)
+where
+    T: RefsOnly<Referent = ()>,
+{
+}
+
 fn multiple_constraints_normalizes_to_different<T, U, V>(_: T, _: U)
 where
     T: IntoIterator<Item = U>,

tests/ui/needless_borrow.stderr

@@ -157,19 +157,19 @@ LL |     let _ = Some("").unwrap_or(&"");
    |                                ^^^ help: change this to: `""`
 
 error: this expression borrows a value the compiler would automatically borrow
-  --> $DIR/needless_borrow.rs:186:13
+  --> $DIR/needless_borrow.rs:187:13
    |
 LL |             (&self.f)()
    |             ^^^^^^^^^ help: change this to: `(self.f)`
 
 error: this expression borrows a value the compiler would automatically borrow
-  --> $DIR/needless_borrow.rs:195:13
+  --> $DIR/needless_borrow.rs:196:13
    |
 LL |             (&mut self.f)()
    |             ^^^^^^^^^^^^^ help: change this to: `(self.f)`
 
 error: the borrowed expression implements the required traits
-  --> $DIR/needless_borrow.rs:283:55
+  --> $DIR/needless_borrow.rs:298:55
    |
 LL |         let _ = std::process::Command::new("ls").args(&["-a", "-l"]).status().unwrap();
    |                                                       ^^^^^^^^^^^^^ help: change this to: `["-a", "-l"]`