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Repository Rebuild System

Source file: Modules/rebuild.py

The rebuild system reconstructs complete file states from commit history. It powers restore, diff, status comparisons, checkout, merge, revert, and clone.

Core Idea

Leaf does not store every commit as a complete copy of the project. Instead:

  1. The first commit stores a complete snapshot.
  2. Later commits store line-based diffs and deleted-file lists.
  3. Rebuild walks the first-parent chain from the first relevant commit to the requested commit.
  4. Each snapshot or diff is applied to an in-memory file map.

Rebuild Flow

requested commit
      │
      ▼
first-parent chain
      │
      ▼
oldest commit → newest commit
      │
      ├── snapshot: copy full file contents into memory
      └── diff: apply additions/context lines and deletions
      │
      ▼
complete file state

Functions

leaf_rebuild(commit_id, log)

Returns a dictionary representing the repository files at a commit:

{
    "path/to/file.txt": ["line 1\n", "line 2\n"]
}

Behavior:

  • Returns {} when no commit ID is supplied.
  • Builds a commit lookup map from log.
  • Calculates the reversed first-parent chain.
  • Loads snapshot files for snapshot commits.
  • Removes files listed in each diff commit’s deleted field.
  • Applies stored diff lines to reconstruct changed files.

write_working_tree(files)

Writes a rebuilt file map into the project directory.

Behavior:

  • Finds currently trackable files.
  • Removes files that are no longer present in the target state.
  • Creates missing directories.
  • Writes each target file’s content.

Important Limitations

  • Rebuild follows the first-parent chain. Merge commits store multiple parents, but file reconstruction uses the mainline path for deterministic rebuild behavior.
  • Leaf stores text content as lines. Binary files are skipped by the commit-state capture process.

Commands That Depend on Rebuild

Command How rebuild is used
leaf restore Recreates the selected commit and writes it to disk.
leaf diff Compares rebuilt commit state with the working tree.
leaf status Compares rebuilt HEAD state with current files.
leaf checkout Writes branch state or saved session to disk.
leaf merge Rebuilds base, target, and source commits.
leaf revert Rebuilds before/after states for the reverted commit.
leaf clone Rebuilds the cloned branch into the destination directory.