[PATCH v3] 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 plain.

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    |    4 ++-
 5 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index a8e0876..a1e36d7 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -635,10 +635,10 @@ 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..fd999fb 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_NORMAL,	/* 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..186eff8 100755
--- a/t/t4034-diff-words.sh
+++ b/t/t4034-diff-words.sh
@@ -8,6 +8,7 @@ test_expect_success setup '
 
 	git config diff.color.old red
 	git config diff.color.new green
+	git config diff.color.func magenta
 
 '
 
@@ -16,6 +17,7 @@ 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 +72,7 @@ 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: (ad7ace7..) bw/func-color (depends on: master)