Original issue: https://github.com/rust-lang/rust/issues/21195
Relevant PR: https://github.com/rust-lang/rust/pull/30778
Prior to this commit, if a compiletest testcase included the text
"HELP:" or "NOTE:" (note the colons), then it would indicate to the
compiletest suite that we should verify "help" and "note" expected
messages.
This commit updates this check to also check "HELP" and "NOTE" (not the
absense of colons) so that we always verify "help" and "note" expected
messages.
Also change several error messages to refer to "items" rather than
"methods", since associated items that require resolution during type
checking are not always methods.
That is, when offering suggestions for unresolved method calls, avoid
suggesting traits for which implementing the trait for the receiver type
either makes little sense (e.g. type errors, or sugared unboxed
closures), or violates coherence.
The latter is approximated by ensuring that at least one of `{receiver
type, trait}` is local. This isn't precisely correct due to
multidispatch, but the error messages one encounters in such situation
are useless more often than not; it is better to be conservative and
miss some cases, than have overly many false positives (e.g. writing
`some_slice.map(|x| ...)` uselessly suggested that one should implement
`IteratorExt` for `&[T]`, while the correct fix is to call `.iter()`).
Closes#21420.
