Week 2 - M3: Real refs, HEAD, and minigit log

[aman-a-shah]

Owner: @DanisLol
Module: 3 - Commits & branching
File you own: minigit/commits.py
Week: 2 of 10 - Real Bytes on Disk

Fix first - from the Week 1 review

minigit commit -m x crashes: AttributeError: 'CommitManager' object has no attribute 'store'.
__init__ only sets self.store when store is passed. Uncomment the fallbacks:

self.store = store or ObjectStore(repo_path)
self.tree = tree or WorkingTree(repo_path)

Also raise RefNotFoundError -> raise RefNotFoundError(name) so the CLI prints something.

What changes this week

• Week 1 refs lived in self._refs and vanished when the process exited
• Week 2 a ref is a real file: .minigit/refs/heads/<branch>, content = one commit hash + \n
• HEAD is a real file: ref: refs/heads/main\n

Steps

1. Branch week2/m3-real-refs (branch off main after M1 merges)
2. Delete self._refs and self._head. Helpers instead:
   • _ref_path(name) -> self.root / ".minigit" / "refs" / "heads" / name
   • read_head() -> str | None - ref: refs/heads/x -> "x"; raw hash -> detached, return the hash
   • write_head(name) -> write ref: refs/heads/<name>\n
   • read_ref(name) -> str | None - file missing = branch has no commits yet
   • write_ref(name, commit_hash) -> mkdir(parents=True, exist_ok=True), write hash + \n
3. create_commit(tree_hash, parents, author, message):
   • _format_commit stays byte-for-byte identical to Week 1
   • write the commit object, then advance the current branch ref to the new hash
   • a commit that doesn't move a ref is unreachable garbage - moving the ref is the point
4. create_branch(name, commit_hash) -> write_ref; name already exists -> MiniGitError
5. list_branches -> sorted(p.name for p in refs_dir.iterdir()), * marks read_head()
6. switch_branch(name) -> unknown ref = RefNotFoundError(name), else write_head(name)
   • # Week 4 - also resolve ref -> commit -> tree and call self.tree.checkout(tree_hash)
7. minigit commit -m "<msg>" for real:
   • tree_hash = self.tree.build_tree_from_index() (still a stub hash this week - fine)
   • parents = [read_ref(current_branch)], or [] when the branch file doesn't exist yet (root commit)
   • author from .minigit/config if present, else "minigit <minigit@local>"
   • print the short hash: [main a1b2c3d] <msg>
8. New command minigit log:
   • walk from read_ref(current) back through parents, print <hash> <message first line> per commit
   • no commits yet -> print no commits yet, return 0
   • parse the commit body back out of store.read_object(hash) - the format is yours, so is the parser
9. merge stays return None # Week 4 fast-forward / Week 5 three-way
10. Tests tests/test_commits.py - real ObjectStore(tmp_path), drop FakeObjectStore:
    • commit on an empty repo -> zero parent lines, ref file created
    • second commit -> one parent line, points at the first
    • the ref file actually moved
    • create_branch twice -> raises
    • switch_branch("nope") -> RefNotFoundError
    • branch, commit, switch back -> the two branches point at different hashes
    • log output has one line per commit, newest first
11. quality-check green -> commit, push, PR

Notes

• run minigit init (@mahis1067's, landing this week) before touching refs in a test
• branching copies a 40-char string and zero object data - that is why it's instant

Done when

• Week 1 store crash fixed
• refs and HEAD are real files
• create_commit moves the current branch ref
• minigit commit / branch / checkout / log all work across separate CLI calls
• tests use the real object store
• quality-check green
• PR open + reviewed