or_fun_call suggests invalid code by removing type information

[tommilligan]

Summary

Clippy suggests/auto-fixes to invalid code for lint or_fun_call. It's invalid if the inserted value contains type information that is not available elsewhere.

https://rust-lang.github.io/rust-clippy/master/#or_fun_call

Reproducer

Minimal example (working minimal repro available to run at https://github.com/tommilligan/rust-clippy-repro-9790):

use std::collections::HashMap;

pub fn example() {
    let mut parent = HashMap::new();
    let grandchild = parent.entry(2).or_insert(Vec::new());
    grandchild.push(-1);
}

Output:

warning: failed to automatically apply fixes suggested by rustc to crate `clippy_new_after_insert`

after fixes were automatically applied the compiler reported errors within these files:

  * src/lib.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/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[E0282]: type annotations needed for `&mut V`
 --> src/lib.rs:5:9
  |
5 |     let grandchild = parent.entry(2).or_default();
  |         ^^^^^^^^^^
6 |     grandchild.push(-1);
  |                ---- type must be known at this point
  |
help: consider giving `grandchild` an explicit type, where the type for type parameter `V` is specified
  |
5 |     let grandchild: &mut V = parent.entry(2).or_default();
  |                   ++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0282`.
Original diagnostics will follow.

warning: use of `or_insert` followed by a call to `new`
 --> src/lib.rs:5:38
  |
5 |     let grandchild = parent.entry(2).or_insert(Vec::new());
  |                                      ^^^^^^^^^^^^^^^^^^^^^ help: try this: `or_default()`
  |
  = note: `#[warn(clippy::or_fun_call)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call

Version

rustc 1.65.0 (897e37553 2022-11-02)
binary: rustc
commit-hash: 897e37553bba8b42751c67658967889d11ecd120
commit-date: 2022-11-02
host: x86_64-unknown-linux-gnu
release: 1.65.0
LLVM version: 15.0.0

Additional Labels

@rustbot label +I-suggestion-causes-error

[tommilligan]

Added a minimal repro at https://github.com/tommilligan/rust-clippy-repro-9790

I would suggest that a better suggestion in this case would be .or_insert_with(Vec::new), which preserves type information.

[J-ZhengLi]

Looks like this issue has already been fixed, as the minimal repro doesn't trigger any warnings now, I'm guessing it was fixed by these few lines:

rust-clippy/clippy_lints/src/methods/or_fun_call.rs

Lines 43 to 45 in b31bce4

	if !expr_type_is_certain(cx, receiver) {
	return false;
	}

I would suggest that a better suggestion in this case would be .or_insert_with(Vec::new)...

theoretically it should suggest that... don't know if it's a bug or not, I'll wait for next week after my last adjustment in #13085 arrives at nightly rust, to see if that fix it.

@rustbot claim

claim for now in case I forgor~