[PATCH v2] Give the hunk comment its own color

[Bert Wesarg <bert.wesarg@googlemail.com>]

Inspired by the coloring of quilt.

Introduce a separate color for the hunk comment part, i.e. the current function.
Whitespace between hunk header and hunk comment is now printed as plain.

The current default is magenta. But I'm not settled on this. My favorite would
be bold yellow.

Now with updated test suit.

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>

---
 Documentation/config.txt |    8 +++---
 combine-diff.c           |    5 +++-
 diff.c                   |   64 +++++++++++++++++++++++++++++++++++++++++++--
 diff.h                   |    1 +
 t/t4034-diff-words.sh    |    3 +-
 5 files changed, 72 insertions(+), 9 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index cb73d75..421cd50 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -598,10 +598,10 @@ color.diff.<slot>::
 	Use customized color for diff colorization.  `<slot>` specifies
 	which part of the patch to use the specified color, and is one
 	of `plain` (context text), `meta` (metainformation), `frag`
-	(hunk header), `old` (removed lines), `new` (added lines),
-	`commit` (commit headers), or `whitespace` (highlighting
-	whitespace errors). The values of these variables may be specified as
-	in color.branch.<slot>.
+	(hunk header), 'func' (function in hunk header), `old` (removed lines),
+	`new` (added lines), `commit` (commit headers), or `whitespace`
+	(highlighting whitespace errors). The values of these variables may be
+	specified as in color.branch.<slot>.
 
 color.grep::
 	When set to `always`, always highlight matches.  When `false` (or
diff --git a/combine-diff.c b/combine-diff.c
index 5b63af1..6162691 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -524,6 +524,7 @@ static void dump_sline(struct sline *sline, unsigned long cnt, int num_parent,
 	int i;
 	unsigned long lno = 0;
 	const char *c_frag = diff_get_color(use_color, DIFF_FRAGINFO);
+	const char *c_func = diff_get_color(use_color, DIFF_FUNCINFO);
 	const char *c_new = diff_get_color(use_color, DIFF_FILE_NEW);
 	const char *c_old = diff_get_color(use_color, DIFF_FILE_OLD);
 	const char *c_plain = diff_get_color(use_color, DIFF_PLAIN);
@@ -588,7 +589,9 @@ static void dump_sline(struct sline *sline, unsigned long cnt, int num_parent,
 				    comment_end = i;
 			}
 			if (comment_end)
-				putchar(' ');
+				printf("%s%s %s%s", c_reset,
+						    c_plain, c_reset,
+						    c_func);
 			for (i = 0; i < comment_end; i++)
 				putchar(hunk_comment[i]);
 		}
diff --git a/diff.c b/diff.c
index 0d7f5ea..e210525 100644
--- a/diff.c
+++ b/diff.c
@@ -39,6 +39,7 @@ static char diff_colors[][COLOR_MAXLEN] = {
 	GIT_COLOR_GREEN,	/* NEW */
 	GIT_COLOR_YELLOW,	/* COMMIT */
 	GIT_COLOR_BG_RED,	/* WHITESPACE */
+	GIT_COLOR_MAGENTA,	/* FUNCINFO */
 };
 
 static void diff_filespec_load_driver(struct diff_filespec *one);
@@ -60,6 +61,8 @@ static int parse_diff_color_slot(const char *var, int ofs)
 		return DIFF_COMMIT;
 	if (!strcasecmp(var+ofs, "whitespace"))
 		return DIFF_WHITESPACE;
+	if (!strcasecmp(var+ofs, "func"))
+		return DIFF_FUNCINFO;
 	die("bad config variable '%s'", var);
 }
 
@@ -344,6 +347,63 @@ static void emit_add_line(const char *reset,
 	}
 }
 
+static void emit_hunk_line(struct emit_callback *ecbdata,
+			   const char *line, int len)
+{
+	const char *plain = diff_get_color(ecbdata->color_diff, DIFF_PLAIN);
+	const char *frag = diff_get_color(ecbdata->color_diff, DIFF_FRAGINFO);
+	const char *func = diff_get_color(ecbdata->color_diff, DIFF_FUNCINFO);
+	const char *reset = diff_get_color(ecbdata->color_diff, DIFF_RESET);
+	const char *orig_line = line;
+	int orig_len = len;
+	const char *frag_start;
+	int frag_len;
+	const char *part_end = NULL;
+	int part_len = 0;
+
+	/* determine length of @ */
+	while (part_len < len && line[part_len] == '@')
+		part_len++;
+
+	/* find end of frag, (Ie. find second @@) */
+	part_end = memmem(line + part_len, len - part_len,
+			  line, part_len);
+	if (!part_end)
+		return emit_line(ecbdata->file, frag, reset, line, len);
+	/* calculate total length of frag */
+	part_len = (part_end + part_len) - line;
+
+	/* remember frag part, we emit only if we find a space separator */
+	frag_start = line;
+	frag_len = part_len;
+
+	/* consume hunk header */
+	len -= part_len;
+	line += part_len;
+
+	/*
+	 * for empty reminder or empty space sequence (exclusive any newlines
+	 * or carriage returns) emit complete original line as FRAGINFO
+	 */
+	if (!len || !(part_len = strspn(line, " \t")))
+		return emit_line(ecbdata->file, frag, reset,
+				 orig_line, orig_len);
+
+	/* now emit the hunk header as FRAGINFO */
+	emit_line(ecbdata->file, frag, reset, frag_start, frag_len);
+
+	/* print whitespace sep as PLAIN */
+	emit_line(ecbdata->file, plain, reset, line, part_len);
+
+	/* consume whitespace sep */
+	len -= part_len;
+	line += part_len;
+
+	/* print reminder as FUNCINFO */
+	if (len)
+		emit_line(ecbdata->file, func, reset, line, len);
+}
+
 static struct diff_tempfile *claim_diff_tempfile(void) {
 	int i;
 	for (i = 0; i < ARRAY_SIZE(diff_temp); i++)
@@ -781,9 +841,7 @@ static void fn_out_consume(void *priv, char *line, unsigned long len)
 			diff_words_flush(ecbdata);
 		len = sane_truncate_line(ecbdata, line, len);
 		find_lno(line, ecbdata);
-		emit_line(ecbdata->file,
-			  diff_get_color(ecbdata->color_diff, DIFF_FRAGINFO),
-			  reset, line, len);
+		emit_hunk_line(ecbdata, line, len);
 		if (line[len-1] != '\n')
 			putc('\n', ecbdata->file);
 		return;
diff --git a/diff.h b/diff.h
index 2740421..15fcecd 100644
--- a/diff.h
+++ b/diff.h
@@ -130,6 +130,7 @@ enum color_diff {
 	DIFF_FILE_NEW = 5,
 	DIFF_COMMIT = 6,
 	DIFF_WHITESPACE = 7,
+	DIFF_FUNCINFO = 8,
 };
 const char *diff_get_color(int diff_use_color, enum color_diff ix);
 #define diff_get_color_opt(o, ix) \
diff --git a/t/t4034-diff-words.sh b/t/t4034-diff-words.sh
index 21db6e9..64a7c38 100755
--- a/t/t4034-diff-words.sh
+++ b/t/t4034-diff-words.sh
@@ -16,6 +16,7 @@ decrypt_color () {
 		-e 's/.\[1m/<WHITE>/g' \
 		-e 's/.\[31m/<RED>/g' \
 		-e 's/.\[32m/<GREEN>/g' \
+		-e 's/.\[35m/<MAGENTA>/g' \
 		-e 's/.\[36m/<BROWN>/g' \
 		-e 's/.\[m/<RESET>/g'
 }
@@ -70,7 +71,7 @@ cat > expect <<\EOF
 <WHITE>+++ b/post<RESET>
 <BROWN>@@ -1 +1 @@<RESET>
 <RED>h(4)<RESET><GREEN>h(4),hh[44]<RESET>
-<BROWN>@@ -3,0 +4,4 @@ a = b + c<RESET>
+<BROWN>@@ -3,0 +4,4 @@<RESET> <RESET><MAGENTA>a = b + c<RESET>
 
 <GREEN>aa = a<RESET>
 
-- 
tg: (785c58e..) bw/func-color (depends on: master)