[PATCH v3] difftool: Change prompt to display the number of files in the diff queue

@@ -806,6 +806,15 @@ temporary file --- it is removed when 'GIT_EXTERNAL_DIFF' exits.
 +
 For a path that is unmerged, 'GIT_EXTERNAL_DIFF' is called with 1
 parameter, <path>.
++
+For each path 'GIT_EXTERNAL_DIFF' is called, two environment variables,
+'GIT_DIFF_PATH_COUNTER' and 'GIT_DIFF_PATH_TOTAL' are set.
+
+'GIT_DIFF_PATH_COUNTER'::
+	A 1-based counter incremented by one for every path.
+
+'GIT_DIFF_PATH_TOTAL'::
+	The total number of paths.
 
 other
 ~~~~~

@@ -2899,11 +2899,16 @@ static void run_external_diff(const char *pgm,
 			      struct diff_filespec *one,
 			      struct diff_filespec *two,
 			      const char *xfrm_msg,
-			      int complete_rewrite)
+			      int complete_rewrite,
+			      struct diff_options *o)
 {
 	const char *spawn_arg[10];
 	int retval;
 	const char **arg = &spawn_arg[0];
+	struct diff_queue_struct *q = &diff_queued_diff;
+	const char *env[3] = { NULL };
+	char env_counter[50];
+	char env_total[50];
 
 	if (one && two) {
 		struct diff_tempfile *temp_one, *temp_two;

@@ -2928,7 +2933,14 @@ static void run_external_diff(const char *pgm,
 	}
 	*arg = NULL;
 	fflush(NULL);
-	retval = run_command_v_opt(spawn_arg, RUN_USING_SHELL);
+
+	env[0] = env_counter;
+	snprintf(env_counter, sizeof(env_counter), "GIT_DIFF_PATH_COUNTER=%d",
+			++o->diff_path_counter);
+	env[1] = env_total;
+	snprintf(env_total, sizeof(env_total), "GIT_DIFF_PATH_TOTAL=%d", q->nr);
+
+	retval = run_command_v_opt_cd_env(spawn_arg, RUN_USING_SHELL, NULL, env);
 	remove_tempfile();
 	if (retval) {
 		fprintf(stderr, "external diff died, stopping at %s.\n", name);

@@ -3042,7 +3054,7 @@ static void run_diff_cmd(const char *pgm,
 
 	if (pgm) {
 		run_external_diff(pgm, name, other, one, two, xfrm_msg,
-				  complete_rewrite);
+				  complete_rewrite, o);
 		return;
 	}
 	if (one && two)

@@ -3317,6 +3329,8 @@ void diff_setup_done(struct diff_options *options)
 		options->output_format = DIFF_FORMAT_NO_OUTPUT;
 		DIFF_OPT_SET(options, EXIT_WITH_STATUS);
 	}
+
+    options->diff_path_counter = 0;
 }
 
 static int opt_arg(const char *arg, int arg_short, const char *arg_long, int *val)

@@ -164,6 +164,8 @@ struct diff_options {
 	diff_prefix_fn_t output_prefix;
 	int output_prefix_length;
 	void *output_prefix_data;
+
+	int diff_path_counter;
 };
 
 enum color_diff {

@@ -40,7 +40,8 @@ launch_merge_tool () {
 	# the user with the real $MERGED name before launching $merge_tool.
 	if should_prompt
 	then
-		printf "\nViewing: '%s'\n" "$MERGED"
+		printf "\nViewing (%s/%s): '%s'\n" "$GIT_DIFF_PATH_COUNTER" \
+			"$GIT_DIFF_PATH_TOTAL" "$MERGED"
 		if use_ext_cmd
 		then
 			printf "Launch '%s' [Y/n]: " \

@@ -193,6 +193,20 @@ test_expect_success 'GIT_EXTERNAL_DIFF with more than one changed files' '
 	GIT_EXTERNAL_DIFF=echo git diff
 '
 
+write_script external-diff.sh <<\EOF
+echo $GIT_DIFF_PATH_COUNTER of $GIT_DIFF_PATH_TOTAL >>counter.txt
+EOF
+
+test_expect_success 'GIT_EXTERNAL_DIFF path counter/total' '
+	GIT_EXTERNAL_DIFF=./external-diff.sh git diff &&
+	echo "1 of 2" >expect &&
+	head -n 1 counter.txt >actual &&
+	test_cmp expect actual &&
+	echo "2 of 2" >expect &&
+	tail -n 1 counter.txt >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'GIT_EXTERNAL_DIFF generates pretty paths' '
 	touch file.ext &&
 	git add file.ext &&

@@ -2936,7 +2936,7 @@ static void run_external_diff(const char *pgm,
 
 	env[0] = env_counter;
 	snprintf(env_counter, sizeof(env_counter), "GIT_DIFF_PATH_COUNTER=%d",
-			++o->diff_path_counter);
+		 ++o->diff_path_counter);
 	env[1] = env_total;
 	snprintf(env_total, sizeof(env_total), "GIT_DIFF_PATH_TOTAL=%d", q->nr);
 

@@ -3330,7 +3330,7 @@ void diff_setup_done(struct diff_options *options)
 		DIFF_OPT_SET(options, EXIT_WITH_STATUS);
 	}
 
-    options->diff_path_counter = 0;
+	options->diff_path_counter = 0;
 }
 
 static int opt_arg(const char *arg, int arg_short, const char *arg_long, int *val)