Lesson 23 · commit-tree: storing the commit

commit-tree: storing the commit

Building the commit body and storing it deserve to be one command. Today you wrap it as commit-tree, which stores a commit for a given tree and returns its id, and confirm the stored object reads back as a commit.

The goal

Store a commit object with commit-tree and read it back.

Start here - the target

TO DO

Scenario: commit-tree stores a readable commit

Giventhe root tree b7c8f173c30a232f001cc4d77c259e4c99afbbd8, the fixed identity and time, and the message Initial commit

WhenCommitTree(tree, no parents, ident, message) stores the commit

Thenit returns f18e98d326b190d096879422d56d4ac5cf572db1

AndCatFile of that id reports type commit, and the object round-trips through the store

Background

commit-tree is the plumbing command that takes a tree id (and later, parent ids) and writes a commit object, returning its id. It is a thin wrapper over the body assembly from the last lesson plus WriteObject, but making it a named operation gives the rest of the project a clean handle: “commit this tree.” We give it a parents argument now even though we pass none yet, because the very next lesson needs it.

The confirmation is that the commit is a first-class object in the store: cat-file reports its type as commit, and its bytes read back unchanged. Everything in Git is one of a handful of object types in one object database, and commits are no exception. Real git cat-file -p f18e98d3... prints the same tree line, identity lines, and message you stored.

Make it work

// build the body (last lesson) and store it; return the id
func (r *Repo) CommitTree(tree string, parents []string, ident, msg string) (string, error) {
  body := buildCommitBody(tree, parents, ident, msg)
  return r.WriteObject("commit", body)
}

CheckpointDONE

commit-tree stores commits you can read back. Commit and stop here.