Re: [PATCH] builtin-commit: fix partial-commit support

Junio C Hamano [off-list ref] writes:

...
Additionally:

   - read the index file after pre-commit hook returns, as the
     hook can modify it to affect the contents of the commit.

 - remove the temporary index file .git/next-index-* after
   commit is done or aborted.

 - run post-commit hook with the real index file to be used
   after the commit (previously it gave the temporary commit if
   a partial commit was made).

 - resurrect the safety mechanism to refuse partial commits
   during a merge to match the scripted version.

 static char *prepare_index(const char **files, const char *prefix)
 {
 	int fd;
 	struct tree *tree;
-	struct lock_file *next_index_lock;
+	struct path_list partial;
+	const char **pathspec = NULL;
 
 	if (interactive) {
 		interactive_add();
+		commit_style = COMMIT_NORMAL;

This should be COMMIT_AS_IS, to match the scripted version.

+	/*
+	 * A partial commit.
+	 *
+	 * (0) find the set of affected paths [NEEDSWORK]

This [NEEDSWORK] has been resolved.

+	 * (1) get lock on the real index file;
+	 * (2) update the_index with the given paths;
+	 * (3) write the_index out to the real index (still locked);
+	 * (4) get lock on the false index file;
+	 * (5) reset the_index from HEAD, but keep the addition;

This ", but keep the addition" is no longer necessary; the set
of paths discovered in step (0) _will_ include the added paths
that are named by the user in **files.

+	 * (6) update the_index the same way as (2);
+	 * (7) write the_index out to the false index file;
+	 * (8) return the name of the false index file (still locked);
+	 *
+	 * The caller should run hooks on the locked false index, and

 ... "create the commit using the false index", of course.

+	 * (A) if all goes well, commit the real index;
+	 * (B) on failure, rollback the real index;
+	 * In either case, rollback the false index.
+	 */