merge: enable progress reporting for rename detection

The user can enable or disable it explicitly with the new
--progress, but it defaults to checking isatty(2).

This works only with merge-recursive and subtree. In theory
we could pass a progress flag to other strategies, but none
of them support progress at this point, so let's wait until
they grow such a feature before worrying about propagating
it.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/merge-options.txt

@@ -75,9 +75,17 @@ option can be used to override --squash.
 ifndef::git-pull[]
 -q::
 --quiet::
-	Operate quietly.
+	Operate quietly. Implies --no-progress.
 
 -v::
 --verbose::
 	Be verbose.
+
+--progress::
+--no-progress::
+	Turn progress on/off explicitly. If neither is specified,
+	progress is shown if standard error is connected to a terminal.
+	Note that not all merge strategies may support progress
+	reporting.
+
 endif::git-pull[]

builtin/merge.c

@@ -58,6 +58,7 @@ static int option_renormalize;
 static int verbosity;
 static int allow_rerere_auto;
 static int abort_current_merge;
+static int show_progress = -1;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
@@ -200,6 +201,7 @@ static struct option builtin_merge_options[] = {
 	OPT__VERBOSITY(&verbosity),
 	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_END()
 };
 
@@ -659,6 +661,8 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 			o.subtree_shift = "";
 
 		o.renormalize = option_renormalize;
+		o.show_rename_progress =
+			show_progress == -1 ? isatty(2) : show_progress;
 
 		for (x = 0; x < xopts_nr; x++)
 			if (parse_merge_opt(&o, xopts[x]))
@@ -944,6 +948,9 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, builtin_merge_options,
 			builtin_merge_usage, 0);
 
+	if (verbosity < 0 && show_progress == -1)
+		show_progress = 0;
+
 	if (abort_current_merge) {
 		int nargc = 2;
 		const char *nargv[] = {"reset", "--merge", NULL};

merge-recursive.c

@@ -441,6 +441,7 @@ static struct string_list *get_renames(struct merge_options *o,
 			    o->diff_rename_limit >= 0 ? o->diff_rename_limit :
 			    1000;
 	opts.rename_score = o->rename_score;
+	opts.show_rename_progress = o->show_rename_progress;
 	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	if (diff_setup_done(&opts) < 0)
 		die("diff setup failed");

merge-recursive.h

@@ -21,6 +21,7 @@ struct merge_options {
 	int merge_rename_limit;
 	int rename_score;
 	int needed_rename_limit;
+	int show_rename_progress;
 	int call_depth;
 	struct strbuf obuf;
 	struct string_list current_file_set;