---

yaml
---
r: 172895
b: refs/heads/batch
c: 02d0a8b
h: refs/heads/master
i:
  172893: e4ead5d
  172891: 27c8c1f
  172887: b560d63
  172879: 6656f4d
  172863: 648b36b
v: v3

Author: Manishearth

[refs]

@@ -29,7 +29,7 @@ refs/tags/0.12.0: f0c419429ef30723ceaf6b42f9b5a2aeb5d2e2d1
 refs/heads/issue-18208-method-dispatch-2: 9e1eae4fb9b6527315b4441cf8a0f5ca911d1671
 refs/heads/automation-fail: 1bf06495443584539b958873e04cc2f864ab10e4
 refs/heads/issue-18208-method-dispatch-3-quick-reject: 2009f85b9f99dedcec4404418eda9ddba90258a2
-refs/heads/batch: ad7e33efee023822bd63fa6f942c25582ef12a1e
+refs/heads/batch: 02d0a8bbcf0a64339e4279c4ddb4841189ba5069
 refs/heads/building: 126db549b038c84269a1e4fe46f051b2c15d6970
 refs/heads/beta: 44a287e6eb22ec3c2a687fc156813577464017f7
 refs/heads/windistfix: 7608dbad651f02e837ed05eef3d74a6662a6e928

branches/batch/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/batch/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() {
 }