clippy --fix generates broken code for new_without_default when Foo::new has type bounds #16255
Description
Summary
As title; when clippy --fix is run against code containing an arg-less Foo::new() method with generic type bounds, it flags the new_without_default lint, and attempts to fix by emitting an unbounded Default impl (which fails to typecheck).
Obviously this isn't a huge deal because I can just add the bound myself trivially.
Reproducer
Code:
use std::marker::PhantomData; pub struct Foo<T> { marker: PhantomData<T> } impl<T> Foo<T> { pub fn new() -> Self where T: Clone { Self { marker: PhantomData } } } fn main() { Foo::<u64>::new(); println!("Hello, world!"); }Current output:
➜ clippyprob git:(master) 251218000110> cargo clippy --fix Checking clippyprob v0.1.0 (/Users/swwu/clippyprob) warning: failed to automatically apply fixes suggested by rustc to crate `clippyprob` 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[E0277]: the trait bound `T: std::clone::Clone` is not satisfied --> src/main.rs:9:9 | 9 | Self::new() | ^^^^^^^^^^^ the trait `std::clone::Clone` is not implemented for `T` | note: required by a bound in `Foo::<T>::new` --> src/main.rs:15:18 | 14 | pub fn new() -> Self | --- required by a bound in this associated function 15 | where T: Clone | ^^^^^ required by this bound in `Foo::<T>::new` help: consider restricting type parameter `T` with trait `Clone` | 7 | impl<T: std::clone::Clone> Default for Foo<T> { | +++++++++++++++++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0277`. Original diagnostics will follow. warning: you should consider adding a `Default` implementation for `Foo<T>` --> src/main.rs:8:5 | 8 | / pub fn new() -> Self 9 | | where T: Clone 10 | | { 11 | | Self { marker: PhantomData } 12 | | } | |_____^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#new_without_default = note: `#[warn(clippy::new_without_default)]` on by default help: try adding this | 7 + impl<T> Default for Foo<T> { 8 + fn default() -> Self { 9 + Self::new() 10 + } 11 + } | warning: `clippyprob` (bin "clippyprob") generated 1 warning (run `cargo clippy --fix --bin "clippyprob" -p clippyprob` to apply 1 suggestion) Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.56s According to --broken-code, clippy attempts to add the following diff:
7 + impl<T> Default for Foo<T> { 8 + fn default() -> Self { 9 + Self::new() 10 + } 11 + } Desired output:
Clippy fixes it and doesn't exit with compiler errors and a message telling me to open a bug report. Presumably it should be emitting something like this instead:
7 + impl<T> Default for Foo<T> where T: Clone { 8 + fn default() -> Self { 9 + Self::new() 10 + } 11 + } Version
rustc 1.92.0 (ded5c06cf 2025-12-08) binary: rustc commit-hash: ded5c06cf21d2b93bffd5d884aa6e96934ee4234 commit-date: 2025-12-08 host: aarch64-apple-darwin release: 1.92.0 LLVM version: 21.1.3 Additional Labels
No response