Add an optional argument for --color options

Make git-branch, git-show-branch, git-grep, and all the diff-based
programs accept an optional argument <when> for --color.  The argument
is a colorbool: "always", "never", or "auto".  If no argument is given,
"always" is used;  --no-color is an alias for --color=never.  This makes
the command-line interface consistent with other GNU tools, such as `ls'
and `grep', and with the git-config color options.  Note that, without
an argument, --color and --no-color work exactly as before.

To implement this, two internal changes were made:

1. Allow the first argument of git_config_colorbool() to be NULL,
   in which case it returns -1 if the argument isn't "always", "never",
   or "auto".

2. Add OPT_COLOR_FLAG(), OPT__COLOR(), and parse_opt_color_flag_cb()
   to the option parsing library.  The callback uses
   git_config_colorbool(), so color.h is now a dependency
   of parse-options.c.

Signed-off-by: Mark Lodato <lodatom@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/parse-options.c b/parse-options.c
index d218122af..c83035d01 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -2,6 +2,7 @@
 #include "parse-options.h"
 #include "cache.h"
 #include "commit.h"
+#include "color.h"
 
 static int parse_options_usage(const char * const *usagestr,
 			       const struct option *opts);
@@ -599,6 +600,21 @@ int parse_opt_approxidate_cb(const struct option *opt, const char *arg,
 	return 0;
 }
 
+int parse_opt_color_flag_cb(const struct option *opt, const char *arg,
+			    int unset)
+{
+	int value;
+
+	if (!arg)
+		arg = unset ? "never" : (const char *)opt->defval;
+	value = git_config_colorbool(NULL, arg, -1);
+	if (value < 0)
+		return opterror(opt,
+			"expects \"always\", \"auto\", or \"never\"", 0);
+	*(int *)opt->value = value;
+	return 0;
+}
+
 int parse_opt_verbosity_cb(const struct option *opt, const char *arg,
 			   int unset)
 {