Make orphan check diagnostics clearer

closes #22388

Author: Jorge Aparicio

src/librustc_typeck/coherence/orphan.rs

@@ -88,15 +88,10 @@ impl<'cx, 'tcx,'v> visit::Visitor<'v> for OrphanChecker<'cx, 'tcx> {
                     Err(traits::OrphanCheckErr::UncoveredTy(param_ty)) => {
                         if !ty::has_attr(self.tcx, trait_def_id, "old_orphan_check") {
                             span_err!(self.tcx.sess, item.span, E0210,
-                                    "type parameter `{}` is not constrained by any local type; \
-                                     only traits defined in the current crate can be implemented \
-                                     for a type parameter",
+                                    "type parameter `{}` must be used as the type parameter for \
+                                     some local type (e.g. `MyStruct<T>`); only traits defined in \
+                                     the current crate can be implemented for a type parameter",
                                     param_ty.user_string(self.tcx));
-                            self.tcx.sess.span_note(
-                                item.span,
-                                &format!("for a limited time, you can add \
-                                          `#![feature(old_orphan_check)]` to your crate \
-                                          to disable this rule"));
                         }
                     }
                 }

src/test/auxiliary/orphan_check_diagnostics.rs

@@ -0,0 +1,11 @@
+// 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.
+
+pub trait RemoteTrait {}

src/test/compile-fail/coherence-bigint-param.rs

@@ -16,6 +16,6 @@ use lib::Remote1;
 pub struct BigInt;
 
 impl<T> Remote1<BigInt> for T { }
-//~^ ERROR type parameter `T` is not constrained
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/coherence-cow-no-cover.rs

@@ -18,6 +18,6 @@ use lib::{Remote,Pair};
 pub struct Cover<T>(T);
 
 impl<T,U> Remote for Pair<Cover<T>,U> { }
-//~^ ERROR type parameter `U` is not constrained by any local type
+//~^ ERROR type parameter `U` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/coherence-cross-crate-conflict.rs

@@ -16,7 +16,7 @@ extern crate trait_impl_conflict;
 use trait_impl_conflict::Foo;
 
 impl<A> Foo for A {
-    //~^ ERROR type parameter `A` is not constrained
+    //~^ ERROR type parameter `A` must be used as the type parameter for some local type
     //~^^ ERROR E0119
 }
 

src/test/compile-fail/coherence-lone-type-parameter.rs

@@ -13,6 +13,7 @@
 extern crate "coherence-lib" as lib;
 use lib::Remote;
 
-impl<T> Remote for T { } //~ ERROR type parameter `T` is not constrained
+impl<T> Remote for T { }
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/coherence-overlapping-pairs.rs

@@ -16,6 +16,6 @@ use lib::Remote;
 struct Foo;
 
 impl<T> Remote for lib::Pair<T,Foo> { }
-//~^ ERROR type parameter `T` is not constrained
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/coherence-pair-covered-uncovered-1.rs

@@ -18,7 +18,7 @@ use lib::{Remote1, Pair};
 
 pub struct Local<T>(T);
 
-impl<T,U> Remote1<Pair<T,Local<U>>> for i32 { }
-//~^ ERROR type parameter `T` is not constrained
+impl<T, U> Remote1<Pair<T, Local<U>>> for i32 { }
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/coherence-pair-covered-uncovered.rs

@@ -16,6 +16,6 @@ use lib::{Remote, Pair};
 struct Local<T>(T);
 
 impl<T,U> Remote for Pair<T,Local<U>> { }
-//~^ ERROR type parameter `T` is not constrained
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }

src/test/compile-fail/orphan-check-diagnostics.rs

@@ -0,0 +1,23 @@
+// 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.
+
+// aux-build:orphan_check_diagnostics.rs
+// see #22388
+
+extern crate orphan_check_diagnostics;
+
+use orphan_check_diagnostics::RemoteTrait;
+
+trait LocalTrait {}
+
+impl<T> RemoteTrait for T where T: LocalTrait {}
+//~^ ERROR type parameter `T` must be used as the type parameter for some local type
+
+fn main() {}