checkout,merge: disallow overwriting ignored files with --no-overwrite-ignore

Ignored files usually are generated files (e.g. .o files) and can be
safely discarded. However sometimes users may have important files in
working directory, but still want a clean "git status", so they mark
them as ignored files. But in this case, these files should not be
overwritten without asking first.

Enable this use case with --no-overwrite-ignore, where git only sees
tracked and untracked files, no ignored files. Those who mix
discardable ignored files with important ones may have to sort it out
themselves.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -34,6 +34,7 @@ struct checkout_opts {
 	int force_detach;
 	int writeout_stage;
 	int writeout_error;
+	int overwrite_ignore;
 
 	/* not set by parse_options */
 	int branch_exists;
@@ -409,9 +410,11 @@ static int merge_working_tree(struct checkout_opts *opts,
 		topts.gently = opts->merge && old->commit;
 		topts.verbose_update = !opts->quiet;
 		topts.fn = twoway_merge;
-		topts.dir = xcalloc(1, sizeof(*topts.dir));
-		topts.dir->flags |= DIR_SHOW_IGNORED;
-		setup_standard_excludes(topts.dir);
+		if (opts->overwrite_ignore) {
+			topts.dir = xcalloc(1, sizeof(*topts.dir));
+			topts.dir->flags |= DIR_SHOW_IGNORED;
+			setup_standard_excludes(topts.dir);
+		}
 		tree = parse_tree_indirect(old->commit ?
 					   old->commit->object.sha1 :
 					   EMPTY_TREE_SHA1_BIN);
@@ -926,6 +929,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			    3),
 		OPT__FORCE(&opts.force, "force checkout (throw away local modifications)"),
 		OPT_BOOLEAN('m', "merge", &opts.merge, "perform a 3-way merge with the new branch"),
+		OPT_BOOLEAN(0, "overwrite-ignore", &opts.overwrite_ignore, "update ignored files (default)"),
 		OPT_STRING(0, "conflict", &conflict_style, "style",
 			   "conflict style (merge or diff3)"),
 		OPT_BOOLEAN('p', "patch", &patch_mode, "select hunks interactively"),
@@ -937,6 +941,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	memset(&opts, 0, sizeof(opts));
 	memset(&new, 0, sizeof(new));
+	opts.overwrite_ignore = 1;
 
 	gitmodules_config();
 	git_config(git_checkout_config, &opts);

builtin/merge.c

@@ -48,6 +48,7 @@ static int show_diffstat = 1, shortlog_len, squash;
 static int option_commit = 1, allow_fast_forward = 1;
 static int fast_forward_only, option_edit;
 static int allow_trivial = 1, have_message;
+static int overwrite_ignore = 1;
 static struct strbuf merge_msg;
 static struct commit_list *remoteheads;
 static struct strategy **use_strategies;
@@ -207,6 +208,7 @@ static struct option builtin_merge_options[] = {
 	OPT_BOOLEAN(0, "abort", &abort_current_merge,
 		"abort the current in-progress merge"),
 	OPT_SET_INT(0, "progress", &show_progress, "force progress reporting", 1),
+	OPT_BOOLEAN(0, "overwrite-ignore", &overwrite_ignore, "update ignored files (default)"),
 	OPT_END()
 };
 
@@ -773,10 +775,12 @@ int checkout_fast_forward(const unsigned char *head, const unsigned char *remote
 	memset(&trees, 0, sizeof(trees));
 	memset(&opts, 0, sizeof(opts));
 	memset(&t, 0, sizeof(t));
-	memset(&dir, 0, sizeof(dir));
-	dir.flags |= DIR_SHOW_IGNORED;
-	setup_standard_excludes(&dir);
-	opts.dir = &dir;
+	if (overwrite_ignore) {
+		memset(&dir, 0, sizeof(dir));
+		dir.flags |= DIR_SHOW_IGNORED;
+		setup_standard_excludes(&dir);
+		opts.dir = &dir;
+	}
 
 	opts.head_idx = 1;
 	opts.src_index = &the_index;