---

yaml
---
r: 172542
b: refs/heads/auto
c: 02d0a8b
h: refs/heads/master
v: v3

Author: Manishearth

[refs]

@@ -10,7 +10,7 @@ refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: ad7e33efee023822bd63fa6f942c25582ef12a1e
+refs/heads/auto: 02d0a8bbcf0a64339e4279c4ddb4841189ba5069
 refs/heads/servo: af82457af293e2a842ba6b7759b70288da276167
 refs/tags/release-0.6: b4ebcfa1812664df5e142f0134a5faea3918544c
 refs/tags/0.1: b19db808c2793fe2976759b85a355c3ad8c8b336

branches/auto/src/doc/reference.md

@@ -2117,6 +2117,13 @@ macro scope.
   destructors from being run twice. Destructors might be run multiple times on
   the same object with this attribute.
 - `doc` - Doc comments such as `/// foo` are equivalent to `#[doc = "foo"]`.
+- `rustc_on_unimplemented` - Write a custom note to be shown along with the error
+   when the trait is found to be unimplemented on a type.
+   You may use format arguments like `{T}`, `{A}` to correspond to the
+   types at the point of use corresponding to the type parameters of the
+   trait of the same name. `{Self}` will be replaced with the type that is supposed
+   to implement the trait but doesn't. To use this, the `on_unimplemented` feature gate
+   must be enabled.
 
 ### Conditional compilation
 

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

@@ -29,6 +29,9 @@ trait BadAnnotation1 {}
 //~^ 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() {
 }