rustfmt produces different results when run from build.rs script when in workspace crate

[mattdurak]

We have a build.rs script that produces a source file and then runs "rustfmt" on it. We use a "rustfmt.toml" file with style_edition = "2021" to try to get the same behavior as running cargo fmt.

However, when building, we get this output:

impl BlockStorageAllocateBlockAsyncCallbackResult {
    fn decode(src: u32) -> Result<Self, DecodeError> {
        let result = match src {
            1 => BlockStorageAllocateBlockAsyncCallbackResult::Ok,
            2 => BlockStorageAllocateBlockAsyncCallbackResult::AlreadyExists,
            3 => BlockStorageAllocateBlockAsyncCallbackResult::Error,
            _ => return Err(DecodeError::new(format!(
                "Decode BlockStorageAllocateBlockAsyncCallbackResult: Unsupported enum value: {}",
                src
            ))),
        };
        Ok(result)
    }
}

But then running cargo fmt on the same workspace produces this output:

impl BlockStorageAllocateBlockAsyncCallbackResult {
    fn decode(src: u32) -> Result<Self, DecodeError> {
        let result = match src {
            1 => BlockStorageAllocateBlockAsyncCallbackResult::Ok,
            2 => BlockStorageAllocateBlockAsyncCallbackResult::AlreadyExists,
            3 => BlockStorageAllocateBlockAsyncCallbackResult::Error,
            _ => {
                return Err(DecodeError::new(format!(
                "Decode BlockStorageAllocateBlockAsyncCallbackResult: Unsupported enum value: {}",
                src
            )))
            }
        };
        Ok(result)
    }
}

Note the extra braces.

This seems to happen when running from a workspace containing the crate specifically. It is annoying as building will produce code that requires re-running "cargo fmt" (else it fails our PR pipeline)

Minimal reproducible example available here: https://github.com/mattdurak/sample_rustfmt_bug

[ytmimi]

Thanks for the report, and for taking the time to put together the example repo. By the way, What version of rustfmt are you using?

[mattdurak]

rustfmt 1.8.0

[ytmimi]

What's the complete value when you run rustfmt --version? Does it not include a git hash?

[mattdurak]

INFO: detected rust-toolchain file C:\src\TEMP\fmt_bug\rust-toolchain - default toolchain will be overridden by ms-1.86
rustfmt 1.8.0

[mattdurak]

Sorry, that's the internal Microsoft supply-chain version, I just did a repro with rustup 1.86:

rustfmt --version
rustfmt 1.8.0-stable (05f9846f89 2025-03-31)