facebook/flow · error · std::io::Error

invalid file index

Error message

invalid file index

What it means

Serialized Flow heaps reference files by index into a heap file table. When the heap is loaded and a dependency is resolved back to a FileKey, file_from_index bounds-checks the index against the table; an index outside it yields ErrorKind::InvalidData "invalid file index". In practice the heap bytes and the file table disagree — a corrupted, truncated, or version-mismatched saved heap.

Source

Thrown at rust_port/crates/flow_heap/src/transaction.rs:919

        }

        self.with_committed_state(|state| {
            let mut gc_state = state.gc_state.lock();
            gc_state.new_alloc_size = gc_state.new_alloc_size.saturating_add(count);
        });
    }

    fn file_index(file_to_index: &BTreeMap<FileKey, u32>, file: &FileKey) -> u32 {
        *file_to_index
            .get(file)
            .expect("file should have been collected in heap file table")
    }

    fn file_from_index(files: &[FileKey], index: u32) -> io::Result<FileKey> {
        files
            .get(index as usize)
            .map(Dupe::dupe)
            .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "invalid file index"))
    }

    fn collect_dependency_file_keys(dependency: &Dependency, file_keys: &mut BTreeSet<FileKey>) {
        match dependency.target() {
            DependencyTarget::HasteModule(_) => {}
            DependencyTarget::File(file) => {
                file_keys.insert(file.dupe());
            }
        }
    }

    fn collect_resolved_module_file_keys(
        module: &crate::resolved_requires::ResolvedModule,
        file_keys: &mut BTreeSet<FileKey>,
    ) {
        if let Some(dependency) = module.as_dependency() {
            Self::collect_dependency_file_keys(&dependency, file_keys);
        }

View on GitHub (pinned to f88ac94bcf)

Solutions

1. Delete the saved-state/heap artifacts for that project so Flow rebuilds the heap from sources.
2. Make sure the process reading the heap is the same Flow build that wrote it (no mixed versions on PATH or in CI caches).
3. If it recurs, check for disk-full or filesystem corruption during the save path.

Example fix

# before: stale heap written by an older build keeps failing to load
flow check

# after: drop saved state so the heap is rebuilt from sources
rm -rf .flow-saved-state   # or your configured saved-state directory
flow check

fn is_invalid_file_index(e: &std::io::Error) -> bool {
    e.kind() == std::io::ErrorKind::InvalidData && e.to_string().contains("invalid file index")
}

Treat InvalidData 'invalid file index' as a disposable-cache failure: catch it, delete the saved heap/saved-state directory, and rebuild from sources. The heap is derived data — never surface it to users as unrecoverable.

When it happens

Trigger: Loading a saved-state heap whose serialized indices were written against a different file table than the one supplied at read time (format or version change between writer and reader), or a heap file truncated/corrupted by a crash or full disk during save.

Common situations: Upgrading Flow across a heap-format change while reusing saved state from the older build; a process killed mid-save leaving a half-written heap; disk-full during the save leaving truncated shards.

Related errors

• hh_load_heap: invalid magic number
• hh_load_heap: invalid shard count
• Can't decode daemon parameters: {}
• failed to decompress
• failed to deserialize AST

AI-assisted analysis of facebook/flow@f88ac94bcf (2026-08-20). Data as JSON: /api/errors/71c592285a864e37. Report an issue: GitHub.