extensions/git/src/git.ts/Repository/getCommit
class Repository:	async getCommit(ref: string): Promise<Commit> {
		const result = await this.exec(['show', '-s', `--format=${COMMIT_FORMAT}`, '-z', ref]);
		const commits = parseGitCommits(result.stdout);
		if (commits.length === 0) {
			return Promise.reject<Commit>('bad commit format');
		}
		return commits[0];
	}