Add more tests

Author: compiler-errors

Diff for: compiler/rustc_hir_typeck/src/method/probe.rs

@@ -1343,7 +1343,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             // We collapse to a subtrait pick *after* filtering unstable candidates
             // to make sure we don't prefer a unstable subtrait method over a stable
             // supertrait method.
-            if self.tcx.features().supertrait_item_shadowing {
+            if self.tcx.features().supertrait_item_shadowing() {
                 if let Some(pick) =
                     self.collapse_candidates_to_subtrait_pick(self_ty, &applicable_candidates)
                 {

Diff for: tests/ui/methods/supertrait-shadowing/assoc-const.rs

@@ -0,0 +1,23 @@
+//@ run-pass
+//@ check-run-results
+
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+trait A {
+    const CONST: i32;
+}
+impl<T> A for T {
+    const CONST: i32 = 1;
+}
+
+trait B: A {
+    const CONST: i32;
+}
+impl<T> B for T {
+    const CONST: i32 = 2;
+}
+
+fn main() {
+    println!("{}", i32::CONST);
+}

Diff for: tests/ui/methods/supertrait-shadowing/assoc-const.run.stdout

@@ -0,0 +1 @@
+2

Diff for: tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.rs

@@ -0,0 +1,23 @@
+#![feature(supertrait_item_shadowing)]
+
+struct W<T>(T);
+
+trait Upstream {
+    fn hello(&self) {}
+}
+impl<T> Upstream for T {}
+
+trait Downstream: Upstream {
+    fn hello(&self) {}
+}
+impl<T> Downstream for W<T> where T: Foo {}
+
+trait Foo {}
+
+fn main() {
+    let x = W(Default::default());
+    x.hello();
+    //~^ ERROR the trait bound `i32: Foo` is not satisfied
+    //~| WARN trait method `hello` from `Downstream` shadows identically named method from supertrait
+    let _: i32 = x.0;
+}

Diff for: tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.stderr

@@ -0,0 +1,38 @@
+warning: trait method `hello` from `Downstream` shadows identically named method from supertrait
+  --> $DIR/false-subtrait-after-inference.rs:19:7
+   |
+LL |     x.hello();
+   |       ^^^^^
+   |
+note: method from `Downstream` shadows a supertrait method
+  --> $DIR/false-subtrait-after-inference.rs:11:5
+   |
+LL |     fn hello(&self) {}
+   |     ^^^^^^^^^^^^^^^
+note: method from `Upstream` is shadowed by a subtrait method
+  --> $DIR/false-subtrait-after-inference.rs:6:5
+   |
+LL |     fn hello(&self) {}
+   |     ^^^^^^^^^^^^^^^
+   = note: `#[warn(supertrait_item_shadowing)]` on by default
+
+error[E0277]: the trait bound `i32: Foo` is not satisfied
+  --> $DIR/false-subtrait-after-inference.rs:19:7
+   |
+LL |     x.hello();
+   |       ^^^^^ the trait `Foo` is not implemented for `i32`, which is required by `W<_>: Downstream`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/false-subtrait-after-inference.rs:15:1
+   |
+LL | trait Foo {}
+   | ^^^^^^^^^
+note: required for `W<i32>` to implement `Downstream`
+  --> $DIR/false-subtrait-after-inference.rs:13:9
+   |
+LL | impl<T> Downstream for W<T> where T: Foo {}
+   |         ^^^^^^^^^^     ^^^^          --- unsatisfied trait bound introduced here
+
+error: aborting due to 1 previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

Diff for: tests/ui/methods/supertrait-shadowing/out-of-scope.rs

@@ -0,0 +1,25 @@
+//@ run-pass
+//@ check-run-results
+
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+mod out_of_scope {
+    pub trait Subtrait: super::Supertrait {
+        fn hello(&self) {
+            println!("subtrait");
+        }
+    }
+    impl<T> Subtrait for T {}
+}
+
+trait Supertrait {
+    fn hello(&self) {
+        println!("supertrait");
+    }
+}
+impl<T> Supertrait for T {}
+
+fn main() {
+    ().hello();
+}

Diff for: tests/ui/methods/supertrait-shadowing/out-of-scope.run.stdout

@@ -0,0 +1 @@
+supertrait

Diff for: tests/ui/methods/supertrait-shadowing/trivially-false-subtrait.rs

@@ -0,0 +1,26 @@
+//@ check-pass
+
+// Make sure we don't prefer a subtrait that we would've otherwise eliminated
+// in `consider_probe` during method probing.
+
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+struct W<T>(T);
+
+trait Upstream {
+    fn hello(&self) {}
+}
+impl<T> Upstream for T {}
+
+trait Downstream: Upstream {
+    fn hello(&self) {}
+}
+impl<T> Downstream for W<T> where T: Foo {}
+
+trait Foo {}
+
+fn main() {
+    let x = W(1i32);
+    x.hello();
+}

Diff for: tests/ui/methods/supertrait-shadowing/type-dependent.rs

@@ -0,0 +1,29 @@
+//@ run-pass
+//@ check-run-results
+
+// Makes sure we can shadow with type-dependent method syntax.
+
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+trait A {
+    fn hello() {
+        println!("A");
+    }
+}
+impl<T> A for T {}
+
+trait B: A {
+    fn hello() {
+        println!("B");
+    }
+}
+impl<T> B for T {}
+
+fn foo<T>() {
+    T::hello();
+}
+
+fn main() {
+    foo::<()>();
+}

Diff for: tests/ui/methods/supertrait-shadowing/type-dependent.run.stdout

@@ -0,0 +1 @@
+B