Function diff

core/tests/testutils/mod.rs:353–398

Generates a textual diff of `golden` and `generated`. The output is meant to be useful for human consumption when a test fails and is not guaranteed to be in patch format. Returns the empty string when the two files match.

(golden: &Path, generated: &Path)

///
/// Returns the empty string when the two files match.
fn diff(golden: &Path, generated: &Path) -> io::Result<String> {
    match process::Command::new("diff")
        .args([OsStr::new("-u"), golden.as_os_str(), generated.as_os_str()])
        .output()
    {
        Ok(result) => {
            let Some(code) = result.status.code() else {
                return Err(io::Error::other("diff crashed"));
            };
            let Ok(stdout) = String::from_utf8(result.stdout) else {
                return Err(io::Error::other("diff printed non-UTF8 content to stdout"));
            };
            let Ok(stderr) = String::from_utf8(result.stderr) else {
                return Err(io::Error::other("diff printed non-UTF8 content to stderr"));
            };

            let mut diff = stdout;
            diff.push_str(&stderr);
            if code == 0 && !diff.is_empty() {
                return Err(io::Error::other("diff succeeded but output is not empty"));
            } else if code != 0 && diff.is_empty() {
                return Err(io::Error::other("diff succeeded but output is empty"));
            }

            Ok(diff)
        }

        Err(e) if e.kind() == io::ErrorKind::NotFound => {
            let left = fs::read_to_string(golden)?;
            let right = fs::read_to_string(generated)?;

            let mut diff = String::new();
            if left != right {
                diff.push_str("Golden\n");
                diff.push_str("======\n");
                diff.push_str(&left);
                diff.push_str("\n\nActual\n");
                diff.push_str("======\n");
                diff.push_str(&right);
            }
            Ok(diff)
        }

        Err(e) => Err(e),
    }
}

#[test]
fn test_diff_same() -> io::Result<()> {