What causes "Source or destination is binary and we can't diff that" in GitoxideLabs/gitoxide?

Confirm the files you intend to diff are text (check for binary content, e.g. no NUL bytes)

Source or destination is binary and we can't diff that

Error message

Source or destination is binary and we can't diff that

What it means

When diffing two blobs, `gix` detects whether the source or destination content is binary (e.g. contains NUL bytes or other non-text data). Since the text diffing machinery only works on tokenizable text, `Operation::SourceOrDestinationIsBinary` is returned and the CLI converts it into this error — git-like behavior of refusing to diff binary files.

Solutions

Confirm the files you intend to diff are text (check for binary content, e.g. no NUL bytes)
Use a diff tool that supports binary files (e.g. git's binary diff or a dedicated compare) instead of this text-diff command
Set appropriate .gitattributes so binary files are marked and handled as such
Strip or normalize the binary content (e.g. re-encode to UTF-8) before diffing

Example fix

// before
let outcome = repo.diff_tree_to_tree(...)  // hits binary pair
// after
if outcome.operation == Operation::SourceOrDestinationIsBinary {
    eprintln!("skipping binary file");
} else { /* proceed with diff */ }

Defensive patterns

Strategy: fallback

Validate before calling

fn looks_binary(data: &[u8]) -> bool {
    data.contains(&0) || data.starts_with(&[0xFF, 0xFE])
}
if looks_binary(&old_data) || looks_binary(&new_data) {
    eprintln!("skipping binary file");
    return Ok(());
}

Try / catch

match outcome.operation {
    Operation::SourceOrDestinationIsBinary => {
        eprintln!("binary file, using fallback compare");
        // fallback: report as binary-changed or use a binary diff
    }
    op => { /* text diff */ }
}

Prevention

Check for NUL bytes / use a binary-detection heuristic before text-diffing blobs
Mark binary files in .gitattributes
Handle Operation::SourceOrDestinationIsBinary explicitly in your match arms instead of assuming text

When it happens

Trigger: Calling `file` in gitoxide-core/src/repository/diff.rs on a pair of blobs where either the old or new object's buffer is classified as binary, producing `Operation::SourceOrDestinationIsBinary` in the diff outcome.

Common situations: Diffing images, compiled artifacts, or files with NUL bytes/odd encodings; a file saved in UTF-16 or with a stray NUL byte gets classified as binary even though it looks textual.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of GitoxideLabs/gitoxide@e73179060b (2026-09-08). Data as JSON: /api/errors/a22f8c1284273614. Report an issue: GitHub.

Appendix: source

Thrown at gitoxide-core/src/repository/diff.rs:197

    resource_cache.set_resource(
        new_blob_id,
        gix::object::tree::EntryKind::Blob,
        new_path.as_ref(),
        gix::diff::blob::ResourceKind::NewOrDestination,
        &repo.objects,
    )?;

    let outcome = resource_cache.prepare_diff()?;

    use gix::diff::blob::platform::prepare_diff::Operation;

    let algorithm = match outcome.operation {
        Operation::InternalDiff { algorithm } => algorithm,
        Operation::ExternalCommand { .. } => {
            unreachable!("We disabled that")
        }
        Operation::SourceOrDestinationIsBinary => {
            anyhow::bail!("Source or destination is binary and we can't diff that")
        }
    };

    let interner = gix::diff::blob::InternedInput::new(
        tokens_for_diffing(outcome.old.data.as_slice().unwrap_or_default()),
        tokens_for_diffing(outcome.new.data.as_slice().unwrap_or_default()),
    );

    let diff = gix::diff::blob::diff_with_slider_heuristics(algorithm, &interner);
    let rendered = gix::diff::blob::UnifiedDiff::new(
        &diff,
        &interner,
        gix::diff::blob::unified_diff::ConsumeBinaryHunk::new(BString::default(), "\n"),
        gix::diff::blob::unified_diff::ContextSize::symmetrical(3),
    )
    .consume()?;
    write!(out, "{rendered}")?;

View on GitHub (pinned to e73179060b)