deprecated lint should not warn within a deprecated module

[aturon]

The stability lint was recently changed to warn on use of deprecated items even when they are defined in the same crate. An unintended consequence is that, when an entire module is deprecated, the body of the module will warn on every use of items defined within it.

We should change this behavior, but it's not entirely clear what the rule should be or how to implement it.

[aturon]

cc @sfackler

[steveklabnik]

To reproduce:

#![feature(staged_api)]
#![staged_api]

#[unstable(feature = "lol", issue = "1")]
#[deprecated(since = "1.0.0", reason = "lol")]
mod nope {
    pub fn foo() {}
    pub fn bar() {}
}

fn main() {
    nope::foo();
    nope::bar();
}

this will give both

hello.rs:12:5: 12:14 warning: use of deprecated item: lol, #[warn(deprecated)] on by default
hello.rs:12     nope::foo();
                ^~~~~~~~~
hello.rs:13:5: 13:14 warning: use of deprecated item: lol, #[warn(deprecated)] on by default
hello.rs:13     nope::bar();
                ^~~~~~~~~

It's been a year, with no discussion at all. I'm not sure this is worth doing.

[TimNN]

This just came up again in #35128, although a little bit more surprisingly, due to the expansion of format_args! inside of a deprecated function.

@steveklabnik: If I understand the original issue correctly, I believe your code should continue to warn about the use of deprecated item.

I believe the issue is that the following warning should not happen:

#[deprecated]
mod nope {
    fn foo() {}

    fn bar() {
        foo() //~ WARN use of deprecated item
    }
}

[eddyb]

The fix doesn't seem that hard. depr_map can contain a DefId pointing to the definition marked with the #[deprecated] attribute, instead of Deprecation (which can be obtained on demand).
Then, if the current node and the referenced node both have the same DefId, no warning is issued.

[TimNN]

If nobody has picked this up by then, I'll see if I can come up with a fix for this towards the end of the week.

[cengiz-io]

@eddyb I can work this if nobody else wants to.

LiveEdit: I guess @TimNN wants. 🍀