mozilla/rust — pull request #10844 by huonw (2013-12-07 02:57:14+00:00)
Title: Make error messages from deriving(Foo) point to the deriving declaration as well as the field

Previously something like

struct NotEq;

#[deriving(Eq)]
struct Error {
foo: NotEq
}

would just point to the `foo` field, with no mention of the
`deriving(Eq)`. With this patch, the compiler creates a note saying "in
expansion of #[deriving(Eq)]" pointing to the Eq.

(includes some cleanup/preparation.)