What causes "at least one chunk" in GitoxideLabs/gitoxide?

Validate the index has chunks before calling highest_offset (e.g. check chunks.is_empty() or use a fallible accessor)

at least one chunk

Error message

at least one chunk

What it means

highest_offset() returns the end offset of the last chunk in a chunk file index and asserts via expect that at least one chunk exists. The type's documentation claims one or more chunks are guaranteed (the index requires mandatory chunks at parse time), so an empty chunk list indicates a corrupted or hand-constructed index and panics.

Solutions

Validate the index has chunks before calling highest_offset (e.g. check chunks.is_empty() or use a fallible accessor)
Re-generate or re-read the index file from a valid source; the file is likely corrupt
Use from_bytes/official parse paths which enforce mandatory chunks instead of manual construction
Report the corrupt file scenario if the standard parser can produce an empty chunk list

Example fix

// before
let end = index.highest_offset();
// after
if index.chunks().is_empty() {
    return Err(message("chunk file index has no chunks"));
}
let end = index.highest_offset();

Defensive patterns

Strategy: validation

Validate before calling

// Guard before using an index whose chunks you did not get from the official parser:
if index.chunks().is_empty() { return Err(anyhow!("chunk index has no chunks")); }

Try / catch

// Since highest_offset panics, pre-validate instead:
let end = if index.chunks().is_empty() { Default::default() } else { index.highest_offset() };

Prevention

Only build chunk indexes via the official parser that enforces mandatory chunks
Validate index files (checksums) before parsing
Re-create corrupted pack/graph index files rather than reading them
Avoid hand-constructing Index values in production code

When it happens

Trigger: Calling highest_offset() on a gix_chunk::file::Index that was constructed with an empty chunks vector — e.g. via direct/low-level construction bypassing the parser that enforces mandatory chunks.

Common situations: Corrupted or truncated multi-pack/commit-graph index files where mandatory chunk entries were dropped; code paths that build Index manually in tests or tooling.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of GitoxideLabs/gitoxide@e73179060b (2026-09-08). Data as JSON: /api/errors/84c428cdd76e2133. Report an issue: GitHub.

Appendix: source

Thrown at gix-chunk/src/file/index.rs:72

    ) -> Result<T, Message> {
        self.chunks
            .iter()
            .find_map(|c| (c.kind == kind).then(|| crate::range::into_usize_or_panic(c.offset.clone())))
            .map(validate)
            .ok_or_else(make_message(kind))
    }

    /// Find a chunk of `kind` and return its data slice based on its offset.
    pub fn data_by_id<'a>(&self, data: &'a [u8], kind: Id) -> Result<&'a [u8], Message> {
        let offset = self.offset_by_id(kind)?;
        Ok(&data[crate::range::into_usize(offset)
            .ok_or_else(|| message("The offsets into the file couldn't be represented by usize"))?])
    }

    /// Return the end offset of the last chunk, which is the highest offset as well.
    /// It's definitely available as we have one or more chunks.
    pub fn highest_offset(&self) -> crate::file::Offset {
        self.chunks.last().expect("at least one chunk").offset.end
    }
}

fn make_message(kind: Id) -> impl FnOnce() -> Message {
    move || message!("Chunk named '{}' was not found in chunk file index", kind.as_bstr())
}

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