Check uses of Self in impls in the compiler rather than during expansion

Closes #23909

src/test/compile-fail/self-impl.rs

@@ -0,0 +1,32 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that unsupported uses of `Self` in impls don't crash
+
+struct Bar;
+
+trait Foo {
+    type Baz;
+}
+
+impl Foo for Bar {
+    type Baz = bool;
+}
+
+impl Bar {
+    fn f() {
+        let _: <Self>::Baz = true;
+//~^ERROR: ambiguous associated type; specify the type using the syntax `<Bar as Trait>::Baz`
+        let _: Self::Baz = true;
+//~^ERROR: ambiguous associated type; specify the type using the syntax `<Bar as Trait>::Baz`
+    }
+}
+
+fn main() {}

src/test/run-pass/self-impl.rs

@@ -22,6 +22,17 @@ impl Foo {
     fn foo(_x: Self, _y: &Self, _z: Box<Self>) -> Self {
         Foo
     }
+
+    fn baz() {
+        // Test that Self cannot be shadowed.
+        type Foo = i32;
+        // There is no empty method on i32.
+        Self::empty();
+
+        let _: Self = Foo;
+    }
+
+    fn empty() {}
 }
 
 // Test uses when implementing a trait and with a type parameter.
@@ -30,12 +41,18 @@ pub struct Baz<X> {
 }
 
 trait Bar<X> {
+    type Qux;
+
     fn bar(x: Self, y: &Self, z: Box<Self>) -> Self;
     fn dummy(&self, x: X) { }
 }
 
 impl Bar<isize> for Box<Baz<isize>> {
+    type Qux = i32;
+
     fn bar(_x: Self, _y: &Self, _z: Box<Self>) -> Self {
+        let _: Self::Qux = 42;
+        let _: <Self as Bar<isize>>::Qux = 42;
         box Baz { f: 42 }
     }
 }
@@ -43,6 +60,6 @@ impl Bar<isize> for Box<Baz<isize>> {
 fn main() {
     let _: Foo = Foo::foo(Foo, &Foo, box Foo);
     let _: Box<Baz<isize>> = Bar::bar(box Baz { f: 42 },
-                                    &box Baz { f: 42 },
-                                    box box Baz { f: 42 });
+                                      &box Baz { f: 42 },
+                                      box box Baz { f: 42 });
 }