Clippy doesn't report error/warnings after cargo check

[b1zzu]

Environment

Project: https://github.com/b1zzu/wifiscanner/tree/clippy-bug (use the clippy-bug branch`)
Cargo: cargo 1.38.0 (23ef9a4ef 2019-08-20)
Clippy: clippy 0.0.212 (3aea860 2019-09-03)

Steps to reproduce

Run cargo clippy after cargo check

cargo check
cargo clippy

Clippy doesn't fail or display any errors.

Expected result

cargo clippy should fails with this errors:

warning: Constants have by default a `'static` lifetime
  --> src/lib.rs:87:22
   |
87 |     const PATH_ENV: &'static str = "PATH";
   |                     -^^^^^^^---- help: consider removing `'static`: `&str`
   |
   = note: `#[warn(clippy::redundant_static_lifetimes)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_static_lifetimes

error: approximate value of `f{32, 64}::consts::PI` found. Consider using it directly
  --> src/lib.rs:85:14
   |
85 |     let _x = 3.14;
   |              ^^^^
   |
   = note: `#[deny(clippy::approx_constant)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant

warning: single-character string constant used as pattern
   --> src/lib.rs:157:16
    |
157 |         .split("\n")
    |                ^^^^ help: try using a char instead: `'\n'`
    |
    = note: `#[warn(clippy::single_char_pattern)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_char_pattern

warning: single-character string constant used as pattern
   --> src/lib.rs:168:36
    |
168 |     for line in network_list.split("\n") {
    |                                    ^^^^ help: try using a char instead: `'\n'`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_char_pattern

error: aborting due to previous error

error: Could not compile `wifiscanner`.

To learn more, run the command again with --verbose.

Workaround

cargo check
cargo clean
cargo clippy

[mati865]

The only reasonable way to fix it is #3837

With nightly toolchain you can use cargo clippy-preview -Z unstable-options as workaround.

[b1zzu]

@mati865 for now I will use cargo clean before clippy

[matthiaskrgr]

It works better if you touch all files of your root crate, this way you don't have to rebuild all the dependencies every time:

find . | grep "\.rs$" | xargs touch ; cargo clippy

[flip1995]

I think we should document this (find . | grep "\.rs$" | xargs touch ; cargo clippy) until cargo clippy (in cargo) is stable.

[b1zzu]

@flip1995 where would you document it? In a new separate Troubleshooting section or as a comment/tips to the step-3-run-clippy

[flip1995]

I think at step-3-run-clippy is enough, since it will be removed anyway in the near future.

[maxbla]

This issue can also be triggered by running clippy multiple times with different options.
main.rs

fn main() {
    let _1 = 1_usize;
    println!("{}", _1);
}

$ cargo clean
$ cargo clippy -- --deny clippy::just_underscores_and_digits
    Compiling ...
error: consider choosing a more descriptive name
...
$ cargo clippy -- --allow clippy::all
$ cargo clippy -- --deny clippy::just_underscores_and_digits

cargo clean fixes this manifestation of the problem also

[sourcefrog]

It looks like this is now fixed?

cargo check
cargo clippy

shows the right errors every time I run it.

clippy 0.0.212 (69f99e7 2019-12-14)
cargo 1.41.0 (626f0f40e 2019-12-03)

[flip1995]

That would surprise me, because we didn't change anything.

I just tested #4612 (comment) and the behavior didn't change there.

[humb1t]

Clippy still depends on check: clippy 0.0.212 (4ee1206 2020-02-01)

[najamelan]

The only reasonable way to fix it is #3837

What about having cargo clippy run the touch **.rs workaround itself? It would depend on platform support for the touch command and globbing, but I feel this issue is important enough to try this.