for-each-ref: introduce %(color:...) for color

Enhance 'git for-each-ref' with color formatting options.  You can now
use the following format in for-each-ref:

  %(color:green)%(refname:short)%(color:reset)

where color names are described in color.branch.*.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: artagnon

Documentation/git-for-each-ref.txt

@@ -101,6 +101,10 @@ HEAD::
 	'*' if HEAD matches current ref (the checked out branch), ' '
 	otherwise.
 
+color::
+	Change output color.  Followed by `:<colorname>`, where names
+	are described in `color.branch.*`.
+
 In addition to the above, for commit and tag objects, the header
 field names (`tree`, `parent`, `object`, `type`, and `tag`) can
 be used to specify the value in the header field.

builtin/for-each-ref.c

@@ -9,6 +9,7 @@
 #include "quote.h"
 #include "parse-options.h"
 #include "remote.h"
+#include "color.h"
 
 /* Quoting styles */
 #define QUOTE_NONE 0
@@ -76,6 +77,7 @@ static struct {
 	{ "symref" },
 	{ "flag" },
 	{ "HEAD" },
+	{ "color" },
 };
 
 /*
@@ -662,8 +664,13 @@ static void populate_value(struct refinfo *ref)
 			    !branch->merge[0]->dst)
 				continue;
 			refname = branch->merge[0]->dst;
-		}
-		else if (!strcmp(name, "flag")) {
+		} else if (!prefixcmp(name, "color:")) {
+			char color[COLOR_MAXLEN] = "";
+
+			color_parse(name + 6, "--format", color);
+			v->s = xstrdup(color);
+			continue;
+		} else if (!strcmp(name, "flag")) {
 			char buf[256], *cp = buf;
 			if (ref->flag & REF_ISSYMREF)
 				cp = copy_advance(cp, ",symref");

t/t6300-for-each-ref.sh

@@ -343,6 +343,23 @@ test_expect_success 'Check for invalid refname format' '
 	test_must_fail git for-each-ref --format="%(refname:INVALID)"
 '
 
+get_color ()
+{
+	git config --get-color no.such.slot "$1"
+}
+
+cat >expected <<EOF
+$(git rev-parse --short refs/heads/master) $(get_color green)master$(get_color reset)
+$(git rev-parse --short refs/remotes/origin/master) $(get_color green)origin/master$(get_color reset)
+$(git rev-parse --short refs/tags/testtag) $(get_color green)testtag$(get_color reset)
+$(git rev-parse --short refs/tags/two) $(get_color green)two$(get_color reset)
+EOF
+
+test_expect_success 'Check %(color:...) ' '
+	git for-each-ref --format="%(objectname:short) %(color:green)%(refname:short)%(color:reset)" >actual &&
+	test_cmp expected actual
+'
+
 cat >expected <<\EOF
 heads/master
 tags/master