1616761 - ./mach lint -l clippy doesn't work correct on some rust code

Status: NEW

(Developer Infrastructure :: Lint and Formatting, defect, P3)

Description

[Sylvestre Ledru [:Sylvestre]]

With the diff

diff --git a/mozglue/static/rust/lib.rs b/mozglue/static/rust/lib.rs
--- a/mozglue/static/rust/lib.rs
+++ b/mozglue/static/rust/lib.rs
@@ -17,16 +17,22 @@ extern "C" {
 }
 
 /// Truncate a string at the closest unicode character boundary
 /// ```
 /// assert_eq!(str_truncate_valid("éà", 3), "é");
 /// assert_eq!(str_truncate_valid("éà", 4), "éè");
 /// ```
 fn str_truncate_valid(s: &str, mut mid: usize) -> &str {
+    let mut a=1;
+    let mut b=1;
+
+    a = b;
+    b = a;
+
     loop {
         if let Some(res) = s.get(..mid) {
             return res;
         }
         mid -= 1;
     }
 }

Warnings are clearly detected by the compiler

 0:04.07    Compiling mozglue-static v0.1.0 (/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust)
 0:04.19 warning: value assigned to `a` is never read
 0:04.19   --> mozglue/static/rust/lib.rs:25:13
 0:04.19    |
 0:04.19 25 |     let mut a=1;
 0:04.19    |             ^
 0:04.19    |

but ./mach lint -l clippy fails to report any issue:

% ./mach lint -l clippy mozglue/static/rust/lib.rs -v
09:02:38.862 clippy (2174047) | Passing the following paths:
/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust/lib.rs
09:02:38.891 clippy (2174047) | Path = /home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust/lib.rs
09:02:38.891 clippy (2174047) | Path translated to = /home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust/Cargo.toml
09:02:38.891 clippy (2174047) | Command: ['/home/sylvestre/.cargo/bin/cargo', 'clean', '--manifest-path', '/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust/Cargo.toml']
09:02:38.938 clippy (2174047) | Command: ['/home/sylvestre/.cargo/bin/cargo', 'clippy', '--message-format=json', '--manifest-path', '/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust/Cargo.toml']
09:02:42.862 clippy (2174047) | Could not parse the output:
09:02:42.863 clippy (2174047) | clippy output: b'   Compiling cc v1.0.47'
09:02:42.863 clippy (2174047) | Could not parse the output:
09:02:42.863 clippy (2174047) | clippy output: b'    Checking arrayvec v0.5.1'
09:02:42.863 clippy (2174047) | Could not parse the output:
09:02:42.863 clippy (2174047) | clippy output: b'   Compiling mozglue-static v0.1.0 (/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust)'
09:02:42.863 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b'error: failed to run custom build command for `mozglue-static v0.1.0 (/home/sylvestre/dev/mozilla/autoland.hg/mozglue/static/rust)`'
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b''
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b'Caused by:'
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b"  process didn't exit successfully: `/home/sylvestre/dev/mozilla/autoland.hg/target/debug/build/mozglue-static-0a8c877e8e3fa413/build-script-build` (exit code: 101)"
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b'--- stderr'
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b"thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /rustc/5e1a799842ba6ed4a57e91f7ab9435947482f7d8/src/libcore/macros/mod.rs:15:40"
09:02:42.864 clippy (2174047) | Could not parse the output:
09:02:42.864 clippy (2174047) | clippy output: b'note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.'
09:02:42.865 clippy (2174047) | Could not parse the output:
09:02:42.865 clippy (2174047) | clippy output: b''
09:02:42.865 clippy (2174047) | Finished in 4.09 seconds
✖ 0 problems (0 errors, 0 warnings)