git config --get-colorbool

This adds an option to help scripts find out color settings from
the configuration file.

    git config --get-colorbool color.diff

inspects color.diff variable, and exits with status 0 (i.e. success) if
color is to be used.  It exits with status 1 otherwise.

If a script wants "true"/"false" answer to the standard output of the
command, it can pass an additional boolean parameter to its command
line, telling if its standard output is a terminal, like this:

    git config --get-colorbool color.diff true

When called like this, the command outputs "true" to its standard output
if color is to be used (i.e. "color.diff" says "always", "auto", or
"true"), and "false" otherwise.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 58 insertions, 7 deletions

diff --git a/Documentation/git-config.txt b/Documentation/git-config.txt
index 7640450787..98509b4f44 100644
--- a/Documentation/git-config.txt
+++ b/Documentation/git-config.txt
@@ -21,6 +21,7 @@ SYNOPSIS
 'git-config' [<file-option>] --remove-section name
 'git-config' [<file-option>] [-z|--null] -l | --list
 'git-config' [<file-option>] --get-color name [default]
+'git-config' [<file-option>] --get-colorbool name [stdout-is-tty]
 
 DESCRIPTION
 -----------
@@ -135,6 +136,15 @@ See also <<FILES>>.
 	output without getting confused e.g. by values that
 	contain line breaks.
 
+--get-colorbool name [stdout-is-tty]::
+
+	Find the color setting for `name` (e.g. `color.diff`) and output
+	"true" or "false".  `stdout-is-tty` should be either "true" or
+	"false", and is taken into account when configuration says
+	"auto".  If `stdout-is-tty` is missing, then checks the standard
+	output of the command itself, and exits with status 0 if color
+	is to be used, or exits with status 1 otherwise.
+
 --get-color name default::
 
 	Find the color configured for `name` (e.g. `color.diff.new`) and
diff --git a/builtin-branch.c b/builtin-branch.c
index c64768beb2..089cae5929 100644
--- a/builtin-branch.c
+++ b/builtin-branch.c
@@ -65,7 +65,7 @@ static int parse_branch_color_slot(const char *var, int ofs)
 static int git_branch_config(const char *var, const char *value)
 {
 	if (!strcmp(var, "color.branch")) {
-		branch_use_color = git_config_colorbool(var, value);
+		branch_use_color = git_config_colorbool(var, value, -1);
 		return 0;
 	}
 	if (!prefixcmp(var, "color.branch.")) {
diff --git a/builtin-config.c b/builtin-config.c
index 6175dc3738..d10b03f50c 100644
--- a/builtin-config.c
+++ b/builtin-config.c
@@ -3,7 +3,7 @@
 #include "color.h"
 
 static const char git_config_set_usage[] =
-"git-config [ --global | --system | [ -f | --file ] config-file ] [ --bool | --int ] [ -z | --null ] [--get | --get-all | --get-regexp | --replace-all | --add | --unset | --unset-all] name [value [value_regex]] | --rename-section old_name new_name | --remove-section name | --list | --get-color var [default]";
+"git-config [ --global | --system | [ -f | --file ] config-file ] [ --bool | --int ] [ -z | --null ] [--get | --get-all | --get-regexp | --replace-all | --add | --unset | --unset-all] name [value [value_regex]] | --rename-section old_name new_name | --remove-section name | --list | --get-color var [default] | --get-colorbool name [stdout-is-tty]";
 
 static char *key;
 static regex_t *key_regexp;
@@ -208,6 +208,43 @@ static int get_color(int argc, const char **argv)
 	return 0;
 }
 
+static int stdout_is_tty;
+static int get_colorbool_found;
+static int git_get_colorbool_config(const char *var, const char *value)
+{
+	if (!strcmp(var, get_color_slot))
+		get_colorbool_found =
+			git_config_colorbool(var, value, stdout_is_tty);
+	return 0;
+}
+
+static int get_colorbool(int argc, const char **argv)
+{
+	/*
+	 * git config --get-colorbool <slot> [<stdout-is-tty>]
+	 *
+	 * returns "true" or "false" depending on how <slot>
+	 * is configured.
+	 */
+
+	if (argc == 2)
+		stdout_is_tty = git_config_bool("command line", argv[1]);
+	else if (argc == 1)
+		stdout_is_tty = isatty(1);
+	else
+		usage(git_config_set_usage);
+	get_colorbool_found = 0;
+	get_color_slot = argv[0];
+	git_config(git_get_colorbool_config);
+
+	if (argc == 1) {
+		return get_colorbool_found ? 0 : 1;
+	} else {
+		printf("%s\n", get_colorbool_found ? "true" : "false");
+		return 0;
+	}
+}
+
 int cmd_config(int argc, const char **argv, const char *prefix)
 {
 	int nongit = 0;
@@ -283,6 +320,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 			return 0;
 		} else if (!strcmp(argv[1], "--get-color")) {
 			return get_color(argc-2, argv+2);
+		} else if (!strcmp(argv[1], "--get-colorbool")) {
+			return get_colorbool(argc-2, argv+2);
 		} else
 			break;
 		argc--;
diff --git a/color.c b/color.c
index 97cfbda31a..7bd424a8f6 100644
--- a/color.c
+++ b/color.c
@@ -116,7 +116,7 @@ bad:
 	die("bad config value '%s' for variable '%s'", value, var);
 }
 
-int git_config_colorbool(const char *var, const char *value)
+int git_config_colorbool(const char *var, const char *value, int stdout_is_tty)
 {
 	if (value) {
 		if (!strcasecmp(value, "never"))
@@ -133,7 +133,9 @@ int git_config_colorbool(const char *var, const char *value)
 
 	/* any normal truth value defaults to 'auto' */
  auto_color:
-	if (isatty(1) || (pager_in_use && pager_use_color)) {
+	if (stdout_is_tty < 0)
+		stdout_is_tty = isatty(1);
+	if (stdout_is_tty || (pager_in_use && pager_use_color)) {
 		char *term = getenv("TERM");
 		if (term && strcmp(term, "dumb"))
 			return 1;
diff --git a/color.h b/color.h
index 68098006ed..ff63513d39 100644
--- a/color.h
+++ b/color.h
@@ -4,7 +4,7 @@
 /* "\033[1;38;5;2xx;48;5;2xxm\0" is 23 bytes */
 #define COLOR_MAXLEN 24
 
-int git_config_colorbool(const char *var, const char *value);
+int git_config_colorbool(const char *var, const char *value, int stdout_is_tty);
 void color_parse(const char *var, const char *value, char *dst);
 int color_fprintf(FILE *fp, const char *color, const char *fmt, ...);
 int color_fprintf_ln(FILE *fp, const char *color, const char *fmt, ...);
diff --git a/diff.c b/diff.c
index 6b54959610..be6cf687a4 100644
--- a/diff.c
+++ b/diff.c
@@ -146,7 +146,7 @@ int git_diff_ui_config(const char *var, const char *value)
 		return 0;
 	}
 	if (!strcmp(var, "diff.color") || !strcmp(var, "color.diff")) {
-		diff_use_color_default = git_config_colorbool(var, value);
+		diff_use_color_default = git_config_colorbool(var, value, -1);
 		return 0;
 	}
 	if (!strcmp(var, "diff.renames")) {
diff --git a/wt-status.c b/wt-status.c
index d35386dae1..02dbb751db 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -391,7 +391,7 @@ void wt_status_print(struct wt_status *s)
 int git_status_config(const char *k, const char *v)
 {
 	if (!strcmp(k, "status.color") || !strcmp(k, "color.status")) {
-		wt_status_use_color = git_config_colorbool(k, v);
+		wt_status_use_color = git_config_colorbool(k, v, -1);
 		return 0;
 	}
 	if (!prefixcmp(k, "status.color.") || !prefixcmp(k, "color.status.")) {