lines_filter_map_ok: Incorrect suggestion when `Result` is a type alias

[taiki-e]

Description

Summary

It seems this lint always suggests map_while(Result::ok), but it is incorrect if Result in the current scope is a type alias other than std::io::Result.

Lint Name

lines_filter_map_ok

Reproducer

I tried this code:

#![warn(clippy::lines_filter_map_ok)]

use std::{fs::File, io::*};

pub struct MyError;
pub type Result<T> = std::result::Result<T, MyError>;

fn _f() {
    let _lines = BufReader::new(File::open("some-path").unwrap())
        .lines()
        .filter_map(|res| res.ok());
}

I saw this happen:

warning: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
  --> src/lib.rs:11:10
   |
11 |         .filter_map(|res| res.ok());
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
   |
note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
  --> src/lib.rs:9:18
   |
9  |       let _lines = BufReader::new(File::open("some-path").unwrap())
   |  __________________^
10 | |         .lines()
   | |________________^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#lines_filter_map_ok
note: the lint level is defined here
  --> src/lib.rs:1:9
   |
1  | #![warn(clippy::lines_filter_map_ok)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^

However, the suggested code (map_while(Result::ok)) cases compile error:

error[E0631]: type mismatch in function arguments
    --> src/lib.rs:11:20
     |
11   |         .map_while(Result::ok);
     |          --------- ^^^^^^^^^^
     |          |         |
     |          |         expected due to this
     |          |         found signature defined here
     |          required by a bound introduced by this call
     |
     = note: expected function signature `fn(std::result::Result<_, std::io::Error>) -> _`
                found function signature `fn(std::result::Result<_, MyError>) -> _`
note: required by a bound in `map_while`
    --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:1266:12
     |
1263 |     fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>
     |        --------- required by a bound in this associated function
...
1266 |         P: FnMut(Self::Item) -> Option<B>,
     |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Iterator::map_while`
help: consider wrapping the function in a closure
     |
11   |         .map_while(|arg0: std::result::Result<String, std::io::Error>| Result::ok(/* std::result::Result<String, MyError> */));
     |                    +++++++++++++++++++++++++++++++++++++++++++++++++++           ++++++++++++++++++++++++++++++++++++++++++++

I expected to see this happen: suggest map_while(|res| res.ok())

playground

Version

rustc 1.86.0-nightly (854f22563 2025-01-31)
binary: rustc
commit-hash: 854f22563c8daf92709fae18ee6aed52953835cd
commit-date: 2025-01-31
host: aarch64-apple-darwin
release: 1.86.0-nightly
LLVM version: 19.1.7

Additional Labels

@rustbot label +C-bug +I-suggestion-causes-error

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