Lint method doc comments which contain no examples that call the method

[clarfonthey]

Sort of long explanation for a simple thing: it's very common in Rust to provide code examples in doc comments to explain how a method is used. However, sometimes methods are the same, and we accidentally copy-paste a doc comment which does not actually call the method it's documenting. This should warn by default, because it's probably a mistake.

I don't think that this warning should warn for doc comments which don't contain code examples, just specifically ones that don't call the thing they're documenting. The former would be better for rustfmt, whereas the latter is something that would be good for a linter like clippy.

[mcarton]

I think that is quite hard because we don't ever lint doc examples, but maybe that would be possible somehow, don't know.