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y86-dev opened this issue Mar 25, 2025 · 3 comments · May be fixed by #14470
Open

cast_lossless not triggered by char as u32 #14469

y86-dev opened this issue Mar 25, 2025 · 3 comments · May be fixed by #14470
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C-bug Category: Clippy is not doing the correct thing good-first-issue These issues are a good way to get started with Clippy I-false-negative Issue: The lint should have been triggered on code, but wasn't

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@y86-dev
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y86-dev commented Mar 25, 2025 •
edited by rustbot
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Summary

Casting a char to a u32 is lossless, but the cast_lossless lint doesn't cover it.

Lint Name

cast_lossless

Reproducer

I tried this code:

#![deny(clippy::cast_lossless)]

fn main() {
    let _ = '|' as u32;
}

Playground

I expected to see this happen: Compiler error

error: casts from `char` to `u32` can be expressed infallibly using `From`
 --> src/main.rs:4:13
  |
4 |     let _ = '|' as u32;
  |             ^^^^^^^^^^
  |
  = help: an `as` cast can become silently lossy if the types change in the future
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
note: the lint level is defined here
 --> src/main.rs:1:9
  |
1 | #![deny(clippy::cast_lossless)]
  |         ^^^^^^^^^^^^^^^^^^^^^
help: use `u32::from` instead
  |
4 |     let _ = u32::from('|');
  |             ~~~~~~~~~~~~~~

Instead, this happened:

The code compiled without any issues.

Version

rustc 1.87.0-nightly (1aeb99d24 2025-03-19)
binary: rustc
commit-hash: 1aeb99d248e1b0069110cb03c6f1dcc7b36fd7f3
commit-date: 2025-03-19
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

(also on stable via playground)

This issue has been assigned to @lapla-cogito via this comment.
@y86-dev y86-dev added C-bug Category: Clippy is not doing the correct thing I-false-negative Issue: The lint should have been triggered on code, but wasn't labels Mar 25, 2025
@ojeda ojeda mentioned this issue Mar 25, 2025
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@samueltardieu samueltardieu added the good-first-issue These issues are a good way to get started with Clippy label Mar 25, 2025
@lapla-cogito lapla-cogito linked a pull request Mar 25, 2025 that will close this issue
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@zen-zap
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zen-zap commented Apr 14, 2025

@rustbot claim

@samueltardieu
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@zen-zap It looks like @lapla-cogito has already submitted a pull request to fix the issue but forgot to assign themselves.

@rustbot assign @lapla-cogito

@rustbot rustbot assigned rustbot and unassigned zen-zap Apr 14, 2025
@zen-zap
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zen-zap commented Apr 14, 2025

oh that's fine .. thanks

@samueltardieu samueltardieu assigned rustbot and unassigned rustbot Apr 14, 2025
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C-bug Category: Clippy is not doing the correct thing good-first-issue These issues are a good way to get started with Clippy I-false-negative Issue: The lint should have been triggered on code, but wasn't
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cast_lossless: lint when converting usize, isize, char and float as well lapla-cogito/rust-clippy
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@samueltardieu @rustbot @zen-zap @y86-dev