squash! built-in add -i: allow filtering the modified files list

built-in add -i: allow filtering the modified files list

In the `update` command of `git add -i`, we are primarily interested in the
list of modified files that have worktree (i.e. unstaged) changes.

At the same time, we need to determine _also_ the staged changes, to be
able to produce the full added/deleted information.

The Perl script version of `git add -i` has a parameter of the
`list_modified()` function for that matter. In C, we can be a lot more
precise, using an `enum`.

The C implementation of the filter also has an easier time to avoid
unnecessary work, simply by using an adaptive order of the `diff-index`
and `diff-files` phases, and then skipping files in the second phase
when they have not been seen in the first phase.

Seeing as we change the meaning of the `phase` field, we rename it to
`mode` to reflect that the order depends on the exact invocation of the
`git add -i` command.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

add-interactive.c

@@ -427,7 +427,7 @@ static int pathname_entry_cmp(const void *unused_cmp_data,
 }
 
 struct collection_status {
-	enum { FROM_WORKTREE = 0, FROM_INDEX = 1 } phase;
+	enum { FROM_WORKTREE = 0, FROM_INDEX = 1 } mode;
 
 	const char *reference;
 
@@ -473,7 +473,7 @@ static void collect_changes_cb(struct diff_queue_struct *q,
 		}
 
 		file_item = entry->item;
-		adddel = s->phase == FROM_INDEX ?
+		adddel = s->mode == FROM_INDEX ?
 			&file_item->index : &file_item->worktree;
 		other_adddel = s->phase == FROM_INDEX ?
 			&file_item->worktree : &file_item->index;
@@ -526,9 +526,9 @@ static int get_modified_files(struct repository *r,
 		struct setup_revision_opt opt = { 0 };
 
 		if (filter == INDEX_ONLY)
-			s.phase = i ? FROM_WORKTREE : FROM_INDEX;
+			s.mode = (i == 0) ? FROM_INDEX : FROM_WORKTREE;
 		else
-			s.phase = i ? FROM_INDEX : FROM_WORKTREE;
+			s.mode = (i == 0) ? FROM_WORKTREE : FROM_INDEX;
 		s.skip_unseen = filter && i;
 
 		opt.def = is_initial ?
@@ -544,7 +544,7 @@ static int get_modified_files(struct repository *r,
 		if (ps)
 			copy_pathspec(&rev.prune_data, ps);
 
-		if (s.phase == FROM_INDEX)
+		if (s.mode == FROM_INDEX)
 			run_diff_index(&rev, 1);
 		else {
 			rev.diffopt.flags.ignore_dirty_submodules = 1;