Incorrect warning explicit lifetimes could be elided

[ikezedev]

Summary

I get false positive to remove a lifetime, when indeed that lifetime is used.

Lint Name

needless_lifetimes

Reproducer

I tried this code:

use derivative::Derivative;

struct TestContext;

#[derive(Derivative)]
#[derivative(Debug)]
struct SessionTest<'a> {
    #[derivative(Debug = "ignore")]
    context: &'a TestContext,
}

I saw this happen:

warning: the following explicit lifetimes could be elided: 'a
  --> iam-smoke-tests/tests/sessions.rs:16:20
   |
16 | struct SessionTest<'a> {
   |                    ^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
   = note: `#[warn(clippy::needless_lifetimes)]` on by default
help: elide the lifetimes
   |
16 - struct SessionTest<'a> {
16 + struct SessionTest'_> {

I expected to see this happen:

Version

rustc 1.83.0 (90b35a623 2024-11-26)
binary: rustc
commit-hash: 90b35a6239c3d8bdabc530a6a0816f7ff89a0aaf
commit-date: 2024-11-26
host: x86_64-unknown-linux-gnu
release: 1.83.0
LLVM version: 19.1.1

Additional Labels

No response

[samueltardieu]

The suggested change is also syntactically incorrect: struct SessionTest'_>

[samueltardieu]

This is due to a bug in the derivative crate, which is no longer maintained. derivative generates code but misuses quote::quote_spanned to do so. Using quote instead would fix the problem. This prevents Clippy from distinguishing code generated from the derivative macro attribute from code written by the user. Only the latter should be linted, as indeed the code generated by the macro contains useless references but this should not be reported.

The bug will likely never be fixed in the unmaintained derivative crate, and should no longer be used. See this security advisory for an alternative.