built-in add -p: support interactive.diffFilter

The Perl version supports post-processing the colored diff (that is
generated in addition to the uncolored diff, intended to offer a
prettier user experience) by a command configured via that config
setting, and now the built-in version does that, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

add-interactive.c

@@ -52,6 +52,17 @@ void init_add_i_state(struct add_i_state *s, struct repository *r)
 		diff_get_color(s->use_color, DIFF_FILE_OLD));
 	init_color(r, s, "new", s->file_new_color,
 		diff_get_color(s->use_color, DIFF_FILE_NEW));
+
+	FREE_AND_NULL(s->interactive_diff_filter);
+	git_config_get_string("interactive.difffilter",
+			      &s->interactive_diff_filter);
+}
+
+void clear_add_i_state(struct add_i_state *s)
+{
+	FREE_AND_NULL(s->interactive_diff_filter);
+	memset(s, 0, sizeof(*s));
+	s->use_color = -1;
 }
 
 /*
@@ -1149,6 +1160,7 @@ int run_add_i(struct repository *r, const struct pathspec *ps)
 	strbuf_release(&print_file_item_data.worktree);
 	strbuf_release(&header);
 	prefix_item_list_clear(&commands);
+	clear_add_i_state(&s);
 
 	return res;
 }

add-interactive.h

@@ -15,9 +15,12 @@ struct add_i_state {
 	char context_color[COLOR_MAXLEN];
 	char file_old_color[COLOR_MAXLEN];
 	char file_new_color[COLOR_MAXLEN];
+
+	char *interactive_diff_filter;
 };
 
 void init_add_i_state(struct add_i_state *s, struct repository *r);
+void clear_add_i_state(struct add_i_state *s);
 
 struct repository;
 struct pathspec;

add-patch.c

@@ -398,6 +398,7 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 
 	if (want_color_fd(1, -1)) {
 		struct child_process colored_cp = CHILD_PROCESS_INIT;
+		const char *diff_filter = s->s.interactive_diff_filter;
 
 		setup_child_process(s, &colored_cp, NULL);
 		xsnprintf((char *)args.argv[color_arg_index], 8, "--color");
@@ -407,6 +408,24 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 		argv_array_clear(&args);
 		if (res)
 			return error(_("could not parse colored diff"));
+
+		if (diff_filter) {
+			struct child_process filter_cp = CHILD_PROCESS_INIT;
+
+			setup_child_process(s, &filter_cp,
+					    diff_filter, NULL);
+			filter_cp.git_cmd = 0;
+			filter_cp.use_shell = 1;
+			strbuf_reset(&s->buf);
+			if (pipe_command(&filter_cp,
+					 colored->buf, colored->len,
+					 &s->buf, colored->len,
+					 NULL, 0) < 0)
+				return error(_("failed to run '%s'"),
+					     diff_filter);
+			strbuf_swap(colored, &s->buf);
+		}
+
 		strbuf_complete_line(colored);
 		colored_p = colored->buf;
 		colored_pend = colored_p + colored->len;
@@ -531,6 +550,9 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 						   colored_pend - colored_p);
 			if (colored_eol)
 				colored_p = colored_eol + 1;
+			else if (p != pend)
+				/* colored shorter than non-colored? */
+				goto mismatched_output;
 			else
 				colored_p = colored_pend;
 
@@ -555,6 +577,15 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 		 */
 		hunk->splittable_into++;
 
+	/* non-colored shorter than colored? */
+	if (colored_p != colored_pend) {
+mismatched_output:
+		error(_("mismatched output from interactive.diffFilter"));
+		advise(_("Your filter must maintain a one-to-one correspondence\n"
+			 "between its input and output lines."));
+		return -1;
+	}
+
 	return 0;
 }
 
@@ -1612,6 +1643,7 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 	    parse_diff(&s, ps) < 0) {
 		strbuf_release(&s.plain);
 		strbuf_release(&s.colored);
+		clear_add_i_state(&s.s);
 		return -1;
 	}
 
@@ -1630,5 +1662,6 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 	strbuf_release(&s.buf);
 	strbuf_release(&s.plain);
 	strbuf_release(&s.colored);
+	clear_add_i_state(&s.s);
 	return 0;
 }