Summary
When trying to fix a clippy::single_match lint where the match value is a macro call, cargo clippy --fix is apparently trying to inline the macro, resulting in an error.
Reproducer
I ran cargo clippy --fix on the following code, which triggers the clippy::single_match lint:
macro_rules! foo {
() => {
$crate::bar()
};
}
fn bar() -> Option<usize> {
Some(42)
}
fn main() {
match foo!() {
Some(u) => println!("{}", u),
None => (),
}
}Clippy was not able to automatically fix the lint. This was the full output:
warning: failed to automatically apply fixes suggested by rustc to crate `clippy_bug`
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error: expected expression, found `$`
--> src/main.rs:12:22
|
12 | if let Some(u) = $crate::bar() { println!("{}", u) }
| ^ expected expression
warning: unused macro definition: `foo`
--> src/main.rs:1:14
|
1 | macro_rules! foo {
| ^^^
|
= note: `#[warn(unused_macros)]` on by default
error: aborting due to 1 previous error; 1 warning emitted
Original diagnostics will follow.
warning: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
--> src/main.rs:12:5
|
12 | / match foo!() {
13 | | Some(u) => println!("{}", u),
14 | | None => (),
15 | | }
| |_____^ help: try: `if let Some(u) = $crate::bar() { println!("{}", u) }`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_match
= note: `#[warn(clippy::single_match)]` on by default
warning: `clippy-bug` (bin "clippy-bug") generated 1 warning (run `cargo clippy --fix --bin "clippy-bug"` to apply 1 suggestion)
warning: failed to automatically apply fixes suggested by rustc to crate `clippy_bug`
after fixes were automatically applied the compiler reported errors within these files:
* src/main.rs
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag
The following errors were reported:
error: expected expression, found `$`
--> src/main.rs:12:22
|
12 | if let Some(u) = $crate::bar() { println!("{}", u) }
| ^ expected expression
warning: unused macro definition: `foo`
--> src/main.rs:1:14
|
1 | macro_rules! foo {
| ^^^
|
= note: `#[warn(unused_macros)]` on by default
error: aborting due to 1 previous error; 1 warning emitted
Original diagnostics will follow.
warning: `clippy-bug` (bin "clippy-bug" test) generated 1 warning (1 duplicate)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.07s
Version
rustc 1.85.1 (4eb161250 2025-03-15)
binary: rustc
commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181
commit-date: 2025-03-15
host: x86_64-unknown-linux-gnu
release: 1.85.1
LLVM version: 19.1.7
Additional Labels
Summary
When trying to fix a
clippy::single_matchlint where the match value is a macro call,cargo clippy --fixis apparently trying to inline the macro, resulting in an error.Reproducer
I ran
cargo clippy --fixon the following code, which triggers theclippy::single_matchlint:Clippy was not able to automatically fix the lint. This was the full output:
Version
Additional Labels