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Macro checks thwart unreachable_pub lint #52665
Description
Recently we landed a change which squashes all lints tied to foreign macros, but this can thwart lints like unreachable_pub in unusual fashions. The unreachable_pub lint can't be fixed unless all its warnings are fixed, which means the following examples fails to compile after being fixed:
// bar.rs
#![crate_type = "lib"]
#[macro_export]
macro_rules! a {
(pub static ref $name:ident : $t:ty = $val:expr) => (
pub struct $name { _wut: () }
pub static $name: $t = $val;
)
}and then
// foo.rs
#![crate_type = "lib"]
#![feature(rust_2018_preview)]
#![warn(rust_2018_idioms)]
#[macro_use]
#[allow(macro_use_extern_crate)]
extern crate bar;
mod m1 {
pub struct Foo;
}
mod lookup {
use crate::m1::Foo;
a!(pub static ref F: Foo = Foo);
}
pub fn f() {
drop(&lookup::F);
}compiled with:
$ rustc +nightly bar.rs
$ rustc +nightly foo.rs -L .
warning: unreachable `pub` item
--> foo.rs:10:5
|
10 | pub struct Foo;
| ---^^^^^^^^^^^^
| |
| help: consider restricting its visibility: `crate`
|
note: lint level defined here
--> foo.rs:3:9
|
3 | #![warn(rust_2018_idioms)]
| ^^^^^^^^^^^^^^^^
= note: #[warn(unreachable_pub)] implied by #[warn(rust_2018_idioms)]
= help: or consider exporting it for use by other crates
but the corrected code doesn't compile!
This is a reuced example where a! is lazy_static!, but I believe the issue here is that the lints behind the lazy_static! invocation are being ignored which means that Foo is actually fully public (because F is) and the lint is no longer applicable as a result.
cc @Manishearth, @oli-obk
Activity
oli-obk commentedon Jul 24, 2018
I don't know if this is solvable in general.
Or are you asking for not squashing the lint behind macros? That's easy, just add
report_in_external_macro: truetorust/src/librustc_lint/builtin.rs
Lines 1392 to 1396 in c7cba3d
alexcrichton commentedon Jul 24, 2018
I'm also not sure it's solvable! It may be a bit of a red herring here to say this is related to macro quashing, it's just sort of hiding the real bug.
I think a better way to put this may be that:
unreachable_publint's suggestions don't work unless you apply all the suggestions.lazy_static!'s generated static). In the macro above there's no way to usecratevisibility.unreachable_pubmay not provide correct suggestions.The macro quashing is meaning you don't even see one of the suggestions (the one in the macro invocation), but even if we display the lint it wouldn't be actionable by rustfix anyway.
oli-obk commentedon Jul 24, 2018
So...
For each lint candidate that has not been squished:
This is a bit extreme and might lead to loads of false negatives, so we should check to ensure that
still lints.
Rollup merge of rust-lang#52926 - alexcrichton:trim-idioms-lints, r=o…