fn get_changed_paths_between_trees_internal()

in focus/util/src/git_helper.rs [546:732]

• 152 lines of code
• 4 McCabe index (conditional complexity)

fn get_changed_paths_between_trees_internal(
    repo: &git2::Repository,
    acc: &mut Vec<Vec<PathBuf>>,
    current_path: &[PathBuf],
    lhs: Option<&git2::Tree>,
    rhs: Option<&git2::Tree>,
) -> Result<()> {
    let lhs_entries: Vec<_> = lhs.map(|tree| tree.iter().collect()).unwrap_or_default();
    let lhs_entries: HashMap<&[u8], &git2::TreeEntry> = lhs_entries
        .iter()
        .map(|entry| (entry.name_bytes(), entry))
        .collect();

    let rhs_entries: Vec<_> = rhs.map(|tree| tree.iter().collect()).unwrap_or_default();
    let rhs_entries: HashMap<&[u8], &git2::TreeEntry> = rhs_entries
        .iter()
        .map(|entry| (entry.name_bytes(), entry))
        .collect();

    let all_entry_names: HashSet<&[u8]> = lhs_entries
        .keys()
        .chain(rhs_entries.keys())
        .cloned()
        .collect();
    let entries: HashMap<&[u8], (Option<&git2::TreeEntry>, Option<&git2::TreeEntry>)> =
        all_entry_names
            .into_iter()
            .map(|entry_name| {
                (
                    entry_name,
                    (
                        lhs_entries.get(entry_name).copied(),
                        rhs_entries.get(entry_name).copied(),
                    ),
                )
            })
            .collect();

    for (entry_name, (lhs_entry, rhs_entry)) in entries {
        enum ClassifiedEntry {
            Absent,
            NotATree(git2::Oid, i32),
            Tree(git2::Oid, i32),
        }

        fn classify_entry(entry: Option<&git2::TreeEntry>) -> Result<ClassifiedEntry> {
            let entry = match entry {
                Some(entry) => entry,
                None => return Ok(ClassifiedEntry::Absent),
            };

            let file_mode = entry.filemode_raw();
            match entry.kind() {
                Some(git2::ObjectType::Tree) => Ok(ClassifiedEntry::Tree(entry.id(), file_mode)),
                _ => Ok(ClassifiedEntry::NotATree(entry.id(), file_mode)),
            }
        }

        let get_tree = |oid| {
            match repo.find_tree(oid) {
                Ok(tree) => Ok(tree),
                Err(err) => {
                    Err(anyhow!(
                        "Tree entry {oid:?} was said to be an object of kind tree, but it could not be looked up: {err}",
                    ))
                }
            }
        };

        let full_entry_path = {
            let entry_name = match std::str::from_utf8(entry_name) {
                Ok(entry_name) => entry_name,
                Err(_) => continue,
            };
            let mut full_entry_path = current_path.to_vec();
            full_entry_path.push(PathBuf::from(entry_name));
            full_entry_path
        };
        match (classify_entry(lhs_entry)?, classify_entry(rhs_entry)?) {
            (ClassifiedEntry::Absent, ClassifiedEntry::Absent) => {
                // Shouldn't happen, but there's no issue here.
            }

            (
                ClassifiedEntry::NotATree(lhs_oid, lhs_file_mode),
                ClassifiedEntry::NotATree(rhs_oid, rhs_file_mode),
            ) => {
                if lhs_oid == rhs_oid && lhs_file_mode == rhs_file_mode {
                    // Unchanged file, do nothing.
                } else {
                    // Changed file.
                    acc.push(full_entry_path);
                }
            }

            (ClassifiedEntry::Absent, ClassifiedEntry::NotATree(_, _))
            | (ClassifiedEntry::NotATree(_, _), ClassifiedEntry::Absent) => {
                // Added, removed, or changed file.
                acc.push(full_entry_path);
            }

            (ClassifiedEntry::Absent, ClassifiedEntry::Tree(tree_oid, _))
            | (ClassifiedEntry::Tree(tree_oid, _), ClassifiedEntry::Absent) => {
                // A directory was added or removed. Add all entries from that
                // directory.
                let tree = get_tree(tree_oid)?;
                get_changed_paths_between_trees_internal(
                    repo,
                    acc,
                    &full_entry_path,
                    Some(&tree),
                    None,
                )?;
            }

            (ClassifiedEntry::NotATree(_, _), ClassifiedEntry::Tree(tree_oid, _))
            | (ClassifiedEntry::Tree(tree_oid, _), ClassifiedEntry::NotATree(_, _)) => {
                // A file was changed into a directory. Add both the file and
                // all subdirectory entries as changed entries.
                let tree = get_tree(tree_oid)?;
                get_changed_paths_between_trees_internal(
                    repo,
                    acc,
                    &full_entry_path,
                    Some(&tree),
                    None,
                )?;
                acc.push(full_entry_path);
            }

            (
                ClassifiedEntry::Tree(lhs_tree_oid, lhs_file_mode),
                ClassifiedEntry::Tree(rhs_tree_oid, rhs_file_mode),
            ) => {
                match (
                    (lhs_tree_oid == rhs_tree_oid),
                    // Note that there should only be one possible file mode for
                    // an entry which points to a tree, but it's possible that
                    // some extra non-meaningful bits are set. Should we report
                    // a change in that case? This code takes the conservative
                    // approach and reports a change.
                    (lhs_file_mode == rhs_file_mode),
                ) {
                    (true, true) => {
                        // Unchanged entry, do nothing.
                    }

                    (true, false) => {
                        // Only the directory changed, but none of its contents.
                        acc.push(full_entry_path);
                    }

                    (false, true) => {
                        let lhs_tree = get_tree(lhs_tree_oid)?;
                        let rhs_tree = get_tree(rhs_tree_oid)?;

                        // Only include the files changed in the subtrees, and
                        // not the directory itself.
                        get_changed_paths_between_trees_internal(
                            repo,
                            acc,
                            &full_entry_path,
                            Some(&lhs_tree),
                            Some(&rhs_tree),
                        )?;
                    }

                    (false, false) => {
                        let lhs_tree = get_tree(lhs_tree_oid)?;
                        let rhs_tree = get_tree(rhs_tree_oid)?;

                        get_changed_paths_between_trees_internal(
                            repo,
                            acc,
                            &full_entry_path,
                            Some(&lhs_tree),
                            Some(&rhs_tree),
                        )?;
                        acc.push(full_entry_path);
                    }
                }
            }
        }
    }

    Ok(())
}