reset: support "--mixed --intent-to-add" mode

When --mixed is used, entries could be removed from index if the
target ref does not have them. When "reset" is used in preparation for
commit spliting (in a dirty worktree), it could be hard to track what
files to be added back. The new option --intent-to-add simplifies it
by marking all removed files intent-to-add.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>

Documentation/git-reset.txt

@@ -10,7 +10,7 @@ SYNOPSIS
 [verse]
 'git reset' [-q] [<tree-ish>] [--] <paths>...
 'git reset' (--patch | -p) [<tree-ish>] [--] [<paths>...]
-'git reset' [--soft | --mixed | --hard | --merge | --keep] [-q] [<commit>]
+'git reset' [--soft | --mixed [-N] | --hard | --merge | --keep] [-q] [<commit>]
 
 DESCRIPTION
 -----------
@@ -60,6 +60,9 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	Resets the index but not the working tree (i.e., the changed files
 	are preserved but not marked for commit) and reports what has not
 	been updated. This is the default action.
++
+If `-N` is specified, removed paths are marked as intent-to-add (see
+linkgit:git-add[1]).
 
 --hard::
 	Resets the index and working tree. Any changes to tracked files in the

builtin/reset.c

@@ -116,32 +116,42 @@ static void update_index_from_diff(struct diff_queue_struct *q,
 		struct diff_options *opt, void *data)
 {
 	int i;
+	int intent_to_add = *(int *)data;
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filespec *one = q->queue[i]->one;
-		if (one->mode && !is_null_sha1(one->sha1)) {
-			struct cache_entry *ce;
-			ce = make_cache_entry(one->mode, one->sha1, one->path,
-				0, 0);
-			if (!ce)
-				die(_("make_cache_entry failed for path '%s'"),
-				    one->path);
-			add_cache_entry(ce, ADD_CACHE_OK_TO_ADD |
-				ADD_CACHE_OK_TO_REPLACE);
-		} else
+		int is_missing = !(one->mode && !is_null_sha1(one->sha1));
+		struct cache_entry *ce;
+
+		if (is_missing && !intent_to_add) {
 			remove_file_from_cache(one->path);
+			continue;
+		}
+
+		ce = make_cache_entry(one->mode, one->sha1, one->path,
+				      0, 0);
+		if (!ce)
+			die(_("make_cache_entry failed for path '%s'"),
+			    one->path);
+		if (is_missing) {
+			ce->ce_flags |= CE_INTENT_TO_ADD;
+			set_object_name_for_intent_to_add_entry(ce);
+		}
+		add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 	}
 }
 
 static int read_from_tree(const struct pathspec *pathspec,
-			  unsigned char *tree_sha1)
+			  unsigned char *tree_sha1,
+			  int intent_to_add)
 {
 	struct diff_options opt;
 
 	memset(&opt, 0, sizeof(opt));
 	copy_pathspec(&opt.pathspec, pathspec);
 	opt.output_format = DIFF_FORMAT_CALLBACK;
 	opt.format_callback = update_index_from_diff;
+	opt.format_callback_data = &intent_to_add;
 
 	if (do_diff_cache(tree_sha1, &opt))
 		return 1;
@@ -258,6 +268,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	const char *rev;
 	unsigned char sha1[20];
 	struct pathspec pathspec;
+	int intent_to_add = 0;
 	const struct option options[] = {
 		OPT__QUIET(&quiet, N_("be quiet, only report errors")),
 		OPT_SET_INT(0, "mixed", &reset_type,
@@ -270,6 +281,8 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		OPT_SET_INT(0, "keep", &reset_type,
 				N_("reset HEAD but keep local changes"), KEEP),
 		OPT_BOOL('p', "patch", &patch_mode, N_("select hunks interactively")),
+		OPT_BOOL('N', "intent-to-add", &intent_to_add,
+				N_("record only the fact that removed paths will be added later")),
 		OPT_END()
 	};
 
@@ -327,6 +340,9 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		die(_("%s reset is not allowed in a bare repository"),
 		    _(reset_type_names[reset_type]));
 
+	if (intent_to_add && reset_type != MIXED)
+		die(_("-N can only be used with --mixed"));
+
 	/* Soft reset does not touch the index file nor the working tree
 	 * at all, but requires them in a good order.  Other resets reset
 	 * the index file to the tree object we are switching to. */
@@ -338,7 +354,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 		int newfd = hold_locked_index(lock, 1);
 		if (reset_type == MIXED) {
 			int flags = quiet ? REFRESH_QUIET : REFRESH_IN_PORCELAIN;
-			if (read_from_tree(&pathspec, sha1))
+			if (read_from_tree(&pathspec, sha1, intent_to_add))
 				return 1;
 			refresh_index(&the_index, flags, NULL, NULL,
 				      _("Unstaged changes after reset:"));

cache.h

@@ -489,6 +489,7 @@ extern int add_to_index(struct index_state *, const char *path, struct stat *, i
 extern int add_file_to_index(struct index_state *, const char *path, int flags);
 extern struct cache_entry *make_cache_entry(unsigned int mode, const unsigned char *sha1, const char *path, int stage, int refresh);
 extern int ce_same_name(const struct cache_entry *a, const struct cache_entry *b);
+extern void set_object_name_for_intent_to_add_entry(struct cache_entry *ce);
 extern int index_name_is_other(const struct index_state *, const char *, int);
 extern void *read_blob_data_from_index(struct index_state *, const char *, unsigned long *);
 

read-cache.c

@@ -579,7 +579,7 @@ static struct cache_entry *create_alias_ce(struct cache_entry *ce, struct cache_
 	return new;
 }
 
-static void record_intent_to_add(struct cache_entry *ce)
+void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 {
 	unsigned char sha1[20];
 	if (write_sha1_file("", 0, blob_type, sha1))
@@ -665,7 +665,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		if (index_path(ce->sha1, path, st, HASH_WRITE_OBJECT))
 			return error("unable to index file %s", path);
 	} else
-		record_intent_to_add(ce);
+		set_object_name_for_intent_to_add_entry(ce);
 
 	if (ignore_case && alias && different_name(ce, alias))
 		ce = create_alias_ce(ce, alias);

t/t7102-reset.sh

@@ -535,4 +535,19 @@ test_expect_success 'reset with paths accepts tree' '
 	git diff HEAD --exit-code
 '
 
+test_expect_success 'reset -N keeps removed files as intent-to-add' '
+	echo new-file >new-file &&
+	git add new-file &&
+	git reset -N HEAD &&
+
+	tree=$(git write-tree) &&
+	git ls-tree $tree new-file >actual &&
+	>expect &&
+	test_cmp expect actual &&
+
+	git diff --name-only >actual &&
+	echo new-file >expect &&
+	test_cmp expect actual
+'
+
 test_done