auto merge of #20889 : Manishearth/rust/trait-error, r=nikomatsakis

fixes #20783

r? @nikomatsakis

src/test/compile-fail/on-unimplemented-bad-anno.rs

@@ -0,0 +1,37 @@
+// 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.
+// ignore-tidy-linelength
+
+#![feature(on_unimplemented)]
+
+#![allow(unused)]
+
+#[rustc_on_unimplemented = "test error `{Self}` with `{Bar}` `{Baz}` `{Quux}`"]
+trait Foo<Bar, Baz, Quux>{}
+
+#[rustc_on_unimplemented="a collection of type `{Self}` cannot be built from an iterator over elements of type `{A}`"]
+trait MyFromIterator<A> {
+    /// Build a container with elements from an external iterator.
+    fn my_from_iter<T: Iterator<Item=A>>(iterator: T) -> Self;
+}
+
+#[rustc_on_unimplemented] //~ ERROR this attribute must have a value
+trait BadAnnotation1 {}
+
+#[rustc_on_unimplemented = "Unimplemented trait error on `{Self}` with params `<{A},{B},{C}>`"]
+//~^ ERROR there is no type parameter C on trait BadAnnotation2
+trait BadAnnotation2<A,B> {}
+
+#[rustc_on_unimplemented = "Unimplemented trait error on `{Self}` with params `<{A},{B},{}>`"]
+//~^ only named substitution parameters are allowed
+trait BadAnnotation3<A,B> {}
+
+pub fn main() {
+}

src/test/compile-fail/on-unimplemented.rs

@@ -0,0 +1,38 @@
+// 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.
+// ignore-tidy-linelength
+
+#![feature(on_unimplemented)]
+
+#[rustc_on_unimplemented = "test error `{Self}` with `{Bar}` `{Baz}` `{Quux}`"]
+trait Foo<Bar, Baz, Quux>{}
+
+fn foobar<U: Clone, T: Foo<u8, U, u32>>() -> T {
+
+}
+
+#[rustc_on_unimplemented="a collection of type `{Self}` cannot be built from an iterator over elements of type `{A}`"]
+trait MyFromIterator<A> {
+    /// Build a container with elements from an external iterator.
+    fn my_from_iter<T: Iterator<Item=A>>(iterator: T) -> Self;
+}
+
+fn collect<A, I: Iterator<Item=A>, B: MyFromIterator<A>>(it: I) -> B {
+    MyFromIterator::my_from_iter(it)
+}
+
+pub fn main() {
+    let x = vec!(1u8, 2, 3, 4);
+    let y: Option<Vec<u8>> = collect(x.iter()); // this should give approximately the same error for x.iter().collect()
+    //~^ ERROR
+    //~^^ NOTE a collection of type `core::option::Option<collections::vec::Vec<u8>>` cannot be built from an iterator over elements of type `&u8`
+    let x: String = foobar(); //~ ERROR
+    //~^ NOTE test error `collections::string::String` with `u8` `_` `u32`
+}