librustc: Take the parameter space into account when combining type

parameters.

This can break code that mistakenly used type parameters in place of
`Self`. For example, this will break:

    trait Foo {
        fn bar<X>(u: X) -> Self {
            u
        }
    }

Change this code to not contain a type error. For example:

    trait Foo {
        fn bar<X>(_: X) -> Self {
            self
        }
    }

Closes #15172.

[breaking-change]

src/librustc/middle/typeck/infer/combine.rs

@@ -445,7 +445,8 @@ pub fn super_tys<C:Combine>(this: &C, a: ty::t, b: ty::t) -> cres<ty::t> {
         }
       }
 
-      (&ty::ty_param(ref a_p), &ty::ty_param(ref b_p)) if a_p.idx == b_p.idx => {
+      (&ty::ty_param(ref a_p), &ty::ty_param(ref b_p)) if
+          a_p.idx == b_p.idx && a_p.space == b_p.space => {
         Ok(a)
       }
 

src/test/compile-fail/type-params-in-different-spaces-1.rs

@@ -0,0 +1,25 @@
+// Copyright 2014 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.
+
+use std::num::Num;
+
+trait BrokenAdd: Num {
+    fn broken_add<T>(&self, rhs: T) -> Self {
+        *self + rhs //~ ERROR mismatched types
+    }
+}
+
+impl<T: Num> BrokenAdd for T {}
+
+pub fn main() {
+    let foo: u8 = 0u8;
+    let x: u8 = foo.broken_add("hello darkness my old friend".to_string());
+    println!("{}", x);
+}

src/test/compile-fail/type-params-in-different-spaces-2.rs

@@ -0,0 +1,35 @@
+// Copyright 2014 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.
+
+trait Tr<T> {
+    fn op(T) -> Self;
+}
+
+// these compile as if Self: Tr<U>, even tho only Self: Tr<Self or T>
+trait A:    Tr<Self> {
+    fn test<U>(u: U) -> Self {
+        Tr::op(u)   //~ ERROR expected Tr<U>, but found Tr<Self>
+    }
+}
+trait B<T>: Tr<T> {
+    fn test<U>(u: U) -> Self {
+        Tr::op(u)   //~ ERROR expected Tr<U>, but found Tr<T>
+    }
+}
+
+impl<T> Tr<T> for T {
+    fn op(t: T) -> T { t }
+}
+impl<T> A for T {}
+
+fn main() {
+    std::io::println(A::test((&7306634593706211700, 8)));
+}
+

src/test/compile-fail/type-params-in-different-spaces-3.rs

@@ -0,0 +1,18 @@
+// Copyright 2014 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.
+
+trait Tr {
+    fn test<X>(u: X) -> Self {
+        u   //~ ERROR mismatched types
+    }
+}
+
+fn main() {}
+