librustc: Can mark functions as deprecated.

[luqmana]

#723 - Add a deprecated items check to lint.

So far it actually only works for functions. I'm not exactly sure how to go about doing it for things like types, structs etc and catching only their uses.

[brson]

Awesome. Can you add a test? Here's an example: https://github.com/mozilla/rust/blob/incoming/src/test/compile-fail/lint-deprecated-self.rs

Checking use of deprecated types will require either looking through the types of all the nodes in the type context, or possibly adding a new table of 'used types' to the type context. Types would be added to this table by the type checker during unification.

[luqmana]

Hmm ok. Also, are methods handled differently than regular fn's in the def_map? There's def_fn and def_static_method.

[brson]

I am not familiar enough with resolve to know what's in def_map, but @pcwalton, @nikomatsakis or @catamorphism might be.

[catamorphism]

@luqmana def_fn is just for functions AFAIK. The compiler treats method access like field access, so (regular) methods don't use def_fn or def_static_method. The exception is static methods (declared with static fn).

This should all be documented, but isn't. Feel free to ask follow-up questions...

[catamorphism]

(see middle::typeck::check::method for the gory details)

[luqmana]

So how could I get the ast::def_id associated with a ast::expr_method_call to lookup the ast::item?

[catamorphism]

@luqmana You can't, because the method you're actually calling isn't known until trans time. For example:

trait A { fn f(); }

impl P: A { fn f() {} }
impl Q: A { #[deprecated] fn f() {} }

fn g<T: A>(x: T) {
    x.f();
}

Does g call the deprecated Q method, or the non-deprecated P method? There's no way to know until monomorphization, which is part of trans.

So you could do this check as part of trans (as a sort of link-time lint check) or just punt on allowing impl methods to have a #[deprecated] attribute.

[catamorphism]

I'm not sure what the status of this is; closing. @luqmana -- feel free to open a new pull requests, or ask questions on IRC if you're blocked!