cargo fmt fails to write fixes for "trailing whitespace" despite correct file permissions

[altunenes]

Hi! When running cargo fmt, rustfmt correctly identifies "left behind trailing whitespace" errors, but it fails to write the fixes to the file. It exits with the error warning: rustfmt has failed to format.

This issue occurs even when:

• File and directory permissions are all correct (owner rw- on the file, rwx on the directory).
• The file has no immutable flags (like uchg on macOS).
• The file is demonstrably writable by the same user (e.g., echo " " >> ... works successfully).
• No other programs (like an IDE) have the file open.
• It made other adjustments for this specific file -video.rs- (meaning the fmt command made changes to the file but caused errors in some places).

errors:

➜  cuneus git:(cargo-fmt) cargo fmt
error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:185:185:1
    |
185 |             
    | ^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:190:190:1
    |
190 |             
    | ^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:195:195:1
    |
195 |                         
    | ^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:200:200:1
    |
200 |                             
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:203:203:1
    |
203 |                             
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:218:218:1
    |
218 |                             
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:225:225:1
    |
225 |                             
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:229:229:1
    |
229 |                             
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:243:243:1
    |
243 |                                 
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:246:246:1
    |
246 |                                 
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:250:250:1
    |
250 |                                 
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:254:254:116
    |
254 |                                     .max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal)) 
    |                                                                                                                    ^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:258:258:1
    |
258 |                                 
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:293:293:1
    |
293 |                                 
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:306:306:1
    |
306 |             
    | ^^^^^^^^^^^^
    |

warning: rustfmt has failed to format. See previous 15 errors.

file:
https://github.com/altunenes/cuneus/blob/cargo-fmt/src/gst/video.rs

rustc --version && rustfmt --version && sw_vers
rustc 1.88.0 (6b00bc388 2025-06-23)
rustfmt 1.8.0-stable (6b00bc3880 2025-06-23)
ProductName:		macOS
ProductVersion:		26.0.1
BuildVersion:		25A362

to fix it manually:

sed -i '' 's/[[:space:]]*$//' /Users/enes/Desktop/cuneus/src/gst/video.rs

[Manishearth]

This is intended behavior, it happens when rustfmt is unable to format a line usually due to something specific about the code in that line.

It doesn't happen due to permissions issues or whatever.

[altunenes]

This is intended behavior, it happens when rustfmt is unable to format a line usually due to something specific about the code in that line.

It doesn't happen due to permissions issues or whatever.

Thank you for the clarification! To confirm I understand correctly: Is it this long line (line 254) that rustfmt is unable to format? And because it's failing on this one line, it's intentionally giving up on the entire file and not saving any of the other simple fixes (like the trailing whitespace)?

error[internal]: left behind trailing whitespace
   --> /Users/enes/Desktop/cuneus/src/gst/video.rs:254:254:116
    |
254 |                                     .max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal)) 
    |                                                                                                                    ^
    |

To reiterate, I already solved the problem initially;

sed -i '' 's/[[:space:]]*$//' /Users/enes/Desktop/cuneus/src/gst/video.rs
I'm just trying to understand the logic behind it. :-)

[Manishearth]

Yes, it's the long line. When rustfmt fails to format something it usually just gives up on the entire file iirc.