Consider param-env candidates even if they have errors

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

@@ -244,7 +244,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .param_env
             .caller_bounds()
             .iter()
-            .filter(|p| !p.references_error())
             .filter_map(|p| p.as_trait_clause())
             // Micro-optimization: filter out predicates relating to different traits.
             .filter(|p| p.def_id() == stack.obligation.predicate.def_id())

tests/ui/async-await/in-trait/unconstrained-impl-region.rs

@@ -14,7 +14,6 @@ impl<'a> Actor for () {
 //~^ ERROR the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
     type Message = &'a ();
     async fn on_mount(self, _: impl Inbox<&'a ()>) {}
-    //~^ ERROR the trait bound `impl Inbox<&'a ()>: Inbox<&'a ()>` is not satisfied
 }
 
 fn main() {}

tests/ui/async-await/in-trait/unconstrained-impl-region.stderr

@@ -1,22 +1,9 @@
-error[E0277]: the trait bound `impl Inbox<&'a ()>: Inbox<&'a ()>` is not satisfied
-  --> $DIR/unconstrained-impl-region.rs:16:5
-   |
-LL |     async fn on_mount(self, _: impl Inbox<&'a ()>) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Inbox<&'a ()>` is not implemented for `impl Inbox<&'a ()>`
-   |
-note: required by a bound in `<() as Actor>::on_mount`
-  --> $DIR/unconstrained-impl-region.rs:16:37
-   |
-LL |     async fn on_mount(self, _: impl Inbox<&'a ()>) {}
-   |                                     ^^^^^^^^^^^^^ required by this bound in `<() as Actor>::on_mount`
-
 error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
   --> $DIR/unconstrained-impl-region.rs:13:6
    |
 LL | impl<'a> Actor for () {
    |      ^^ unconstrained lifetime parameter
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0207, E0277.
-For more information about an error, try `rustc --explain E0207`.
+For more information about this error, try `rustc --explain E0207`.

tests/ui/traits/error-reporting/apit-with-bad-path.rs

@@ -0,0 +1,10 @@
+// Ensure that we don't emit an E0270 for "`impl AsRef<Path>: AsRef<Path>` not satisfied".
+
+fn foo(filename: impl AsRef<Path>) {
+    //~^ ERROR cannot find type `Path` in this scope
+    std::fs::write(filename, "hello").unwrap();
+}
+
+fn main() {
+    foo("/tmp/hello");
+}

tests/ui/traits/error-reporting/apit-with-bad-path.stderr

@@ -0,0 +1,14 @@
+error[E0412]: cannot find type `Path` in this scope
+  --> $DIR/apit-with-bad-path.rs:3:29
+   |
+LL | fn foo(filename: impl AsRef<Path>) { 
+   |                             ^^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::path::Path;
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0412`.

tests/ui/traits/error-reporting/where-clause-with-bad-path.rs

@@ -0,0 +1,10 @@
+// Ensure that we don't emit an E0270 for "`impl AsRef<Path>: AsRef<Path>` not satisfied".
+
+fn foo<T: AsRef<Path>>(filename: T) {
+    //~^ ERROR cannot find type `Path` in this scope
+    std::fs::write(filename, "hello").unwrap();
+}
+
+fn main() {
+    foo("/tmp/hello");
+}

tests/ui/traits/error-reporting/where-clause-with-bad-path.stderr

@@ -0,0 +1,14 @@
+error[E0412]: cannot find type `Path` in this scope
+  --> $DIR/where-clause-with-bad-path.rs:3:17
+   |
+LL | fn foo<T: AsRef<Path>>(filename: T) {
+   |                 ^^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::path::Path;
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0412`.