[PATCH 03/19] built-in add -p: show colored hunks by default

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

Just like the Perl version, we now generate two diffs if `color.diff` is
set: one with and one without color. Then we parse them in parallel and
record which hunks start at which offsets in both.

Note that this is a (slight) deviation from the way the Perl version did
it: we are no longer reading the output of `diff-files` line by line
(which is more natural for Perl than for C), but in one go, and parse
everything later, so we might just as well do it in synchrony.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 add-patch.c | 79 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 62 insertions(+), 17 deletions(-)

diff --git a/add-patch.c b/add-patch.c
index d1b1a080e4..79eefa9505 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -4,9 +4,10 @@
 #include "run-command.h"
 #include "argv-array.h"
 #include "pathspec.h"
+#include "color.h"
 
 struct hunk {
-	size_t start, end;
+	size_t start, end, colored_start, colored_end;
 	enum { UNDECIDED_HUNK = 0, SKIP_HUNK, USE_HUNK } use;
 };
 
@@ -15,7 +16,7 @@ struct add_p_state {
 	struct strbuf answer, buf;
 
 	/* parsed diff */
-	struct strbuf plain;
+	struct strbuf plain, colored;
 	struct hunk head;
 	struct hunk *hunk;
 	size_t hunk_nr, hunk_alloc;
@@ -39,26 +40,50 @@ static void setup_child_process(struct add_p_state *s,
 
 static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 {
-	struct strbuf *plain = &s->plain;
+	struct argv_array args = ARGV_ARRAY_INIT;
+	struct strbuf *plain = &s->plain, *colored = NULL;
 	struct child_process cp = CHILD_PROCESS_INIT;
-	char *p, *pend;
-	size_t i;
+	char *p, *pend, *colored_p = NULL, *colored_pend = NULL;
+	size_t i, color_arg_index;
 	struct hunk *hunk = NULL;
 	int res;
 
 	/* Use `--no-color` explicitly, just in case `diff.color = always`. */
-	setup_child_process(s, &cp,
-			 "diff-files", "-p", "--no-color", "--", NULL);
+	argv_array_pushl(&args, "diff-files", "-p", "--no-color", "--", NULL);
+	color_arg_index = args.argc - 2;
 	for (i = 0; i < ps->nr; i++)
-		argv_array_push(&cp.args, ps->items[i].original);
+		argv_array_push(&args, ps->items[i].original);
 
+	setup_child_process(s, &cp, NULL);
+	cp.argv = args.argv;
 	res = capture_command(&cp, plain, 0);
-	if (res)
+	if (res) {
+		argv_array_clear(&args);
 		return error(_("could not parse diff"));
-	if (!plain->len)
+	}
+	if (!plain->len) {
+		argv_array_clear(&args);
 		return 0;
+	}
 	strbuf_complete_line(plain);
 
+	if (want_color_fd(1, -1)) {
+		struct child_process colored_cp = CHILD_PROCESS_INIT;
+
+		setup_child_process(s, &colored_cp, NULL);
+		xsnprintf((char *)args.argv[color_arg_index], 8, "--color");
+		colored_cp.argv = args.argv;
+		colored = &s->colored;
+		res = capture_command(&colored_cp, colored, 0);
+		argv_array_clear(&args);
+		if (res)
+			return error(_("could not parse colored diff"));
+		strbuf_complete_line(colored);
+		colored_p = colored->buf;
+		colored_pend = colored_p + colored->len;
+	}
+	argv_array_clear(&args);
+
 	/* parse hunks */
 	p = plain->buf;
 	pend = p + plain->len;
@@ -82,20 +107,37 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 			memset(hunk, 0, sizeof(*hunk));
 
 			hunk->start = p - plain->buf;
+			if (colored)
+				hunk->colored_start = colored_p - colored->buf;
 		}
 
 		p = eol == pend ? pend : eol + 1;
 		hunk->end = p - plain->buf;
+
+		if (colored) {
+			char *colored_eol = memchr(colored_p, '\n',
+						   colored_pend - colored_p);
+			if (colored_eol)
+				colored_p = colored_eol + 1;
+			else
+				colored_p = colored_pend;
+
+			hunk->colored_end = colored_p - colored->buf;
+		}
 	}
 
 	return 0;
 }
 
 static void render_hunk(struct add_p_state *s, struct hunk *hunk,
-			struct strbuf *out)
+			int colored, struct strbuf *out)
 {
-	strbuf_add(out, s->plain.buf + hunk->start,
-		   hunk->end - hunk->start);
+	if (colored)
+		strbuf_add(out, s->colored.buf + hunk->colored_start,
+			   hunk->colored_end - hunk->colored_start);
+	else
+		strbuf_add(out, s->plain.buf + hunk->start,
+			   hunk->end - hunk->start);
 }
 
 static void reassemble_patch(struct add_p_state *s, struct strbuf *out)
@@ -103,12 +145,12 @@ static void reassemble_patch(struct add_p_state *s, struct strbuf *out)
 	struct hunk *hunk;
 	size_t i;
 
-	render_hunk(s, &s->head, out);
+	render_hunk(s, &s->head, 0, out);
 
 	for (i = 0; i < s->hunk_nr; i++) {
 		hunk = s->hunk + i;
 		if (hunk->use == USE_HUNK)
-			render_hunk(s, hunk, out);
+			render_hunk(s, hunk, 0, out);
 	}
 }
 
@@ -130,12 +172,13 @@ static int patch_update_file(struct add_p_state *s)
 	struct hunk *hunk;
 	char ch;
 	struct child_process cp = CHILD_PROCESS_INIT;
+	int colored = !!s->colored.len;
 
 	if (!s->hunk_nr)
 		return 0;
 
 	strbuf_reset(&s->buf);
-	render_hunk(s, &s->head, &s->buf);
+	render_hunk(s, &s->head, colored, &s->buf);
 	fputs(s->buf.buf, stdout);
 	for (;;) {
 		if (hunk_index >= s->hunk_nr)
@@ -162,7 +205,7 @@ static int patch_update_file(struct add_p_state *s)
 			break;
 
 		strbuf_reset(&s->buf);
-		render_hunk(s, hunk, &s->buf);
+		render_hunk(s, hunk, colored, &s->buf);
 		fputs(s->buf.buf, stdout);
 
 		strbuf_reset(&s->buf);
@@ -252,6 +295,7 @@ int run_add_p(struct repository *r, const struct pathspec *ps)
 					 NULL, NULL, NULL) < 0 ||
 	    parse_diff(&s, ps) < 0) {
 		strbuf_release(&s.plain);
+		strbuf_release(&s.colored);
 		return -1;
 	}
 
@@ -261,5 +305,6 @@ int run_add_p(struct repository *r, const struct pathspec *ps)
 	strbuf_release(&s.answer);
 	strbuf_release(&s.buf);
 	strbuf_release(&s.plain);
+	strbuf_release(&s.colored);
 	return 0;
 }
-- 
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