color: check color.ui in git_default_config()

Back in prehistoric times, our decision on whether or not to
show color by default relied on using a config callback that
either did or didn't load color config like color.diff.
When we introduced color.ui, we put it in the same boat:
commands had to manually respect it by using git_color_config()
or its git_color_default_config() convenience wrapper.

But in 4c7f1819b (make color.ui default to 'auto',
2013-06-10), that changed. Since then, we default color.ui
to auto in all programs, meaning that even plumbing commands
like "git diff-tree --pretty" might colorize the output.
Nobody seems to have complained in the intervening years,
presumably because the "is stdout a tty" check does a good
job of catching the right cases.

But that leaves an interesting curiosity: color.ui defaults
to auto even in plumbing, but you can't actually _disable_
the color via config. So if you really hate color and set
"color.ui" to false, diff-tree will still show color (but
porcelain like git-diff won't).  Nobody noticed that either,
probably because very few people disable color.

One could argue that the plumbing should _always_ disable
color unless an explicit --color option is given on the
command line. But in practice, this creates a lot of
complications for scripts which do want plumbing to show
user-visible output. They can't just pass "--color" blindly;
they need to check the user's config and decide what to
send.

Given that nobody has complained about the current behavior,
let's assume it's a good path, and follow it to its
conclusion: supporting color.ui everywhere.

Note that you can create havoc by setting color.ui=always in
your config, but that's more or less already the case. We
could disallow it entirely, but it is handy for one-offs
like:

  git -c color.ui=always foo >not-a-tty

when "foo" does not take a --color option itself.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -92,7 +92,7 @@ static int git_branch_config(const char *var, const char *value, void *cb)
 			return config_error_nonbool(var);
 		return color_parse(value, branch_colors[slot]);
 	}
-	return git_color_default_config(var, value, cb);
+	return git_default_config(var, value, cb);
 }
 
 static const char *branch_get_color(enum color_branch ix)

builtin/clean.c

@@ -125,8 +125,7 @@ static int git_clean_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	/* inspect the color.ui config variable and others */
-	return git_color_default_config(var, value, cb);
+	return git_default_config(var, value, cb);
 }
 
 static const char *clean_get_color(enum color_clean ix)

builtin/grep.c

@@ -284,7 +284,7 @@ static int wait_all(void)
 static int grep_cmd_config(const char *var, const char *value, void *cb)
 {
 	int st = grep_config(var, value, cb);
-	if (git_color_default_config(var, value, cb) < 0)
+	if (git_default_config(var, value, cb) < 0)
 		st = -1;
 
 	if (!strcmp(var, "grep.threads")) {

builtin/show-branch.c

@@ -554,7 +554,7 @@ static int git_show_branch_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	return git_color_default_config(var, value, cb);
+	return git_default_config(var, value, cb);
 }
 
 static int omit_in_dense(struct commit *commit, struct commit **rev, int n)

color.c

@@ -361,14 +361,6 @@ int git_color_config(const char *var, const char *value, void *cb)
 	return 0;
 }
 
-int git_color_default_config(const char *var, const char *value, void *cb)
-{
-	if (git_color_config(var, value, cb) < 0)
-		return -1;
-
-	return git_default_config(var, value, cb);
-}
-
 void color_print_strbuf(FILE *fp, const char *color, const struct strbuf *sb)
 {
 	if (*color)

config.c

@@ -16,6 +16,7 @@
 #include "string-list.h"
 #include "utf8.h"
 #include "dir.h"
+#include "color.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -1350,6 +1351,9 @@ int git_default_config(const char *var, const char *value, void *dummy)
 	if (starts_with(var, "advice."))
 		return git_default_advice_config(var, value);
 
+	if (git_color_config(var, value, dummy) < 0)
+		return -1;
+
 	if (!strcmp(var, "pager.color") || !strcmp(var, "color.pager")) {
 		pager_use_color = git_config_bool(var,value);
 		return 0;

diff.c

@@ -299,9 +299,6 @@ int git_diff_ui_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	if (git_color_config(var, value, cb) < 0)
-		return -1;
-
 	return git_diff_basic_config(var, value, cb);
 }