config: write to $XDG_CONFIG_HOME/git/config file when appropriate

Teach git to write to $XDG_CONFIG_HOME/git/config if

 - it already exists,
 - $HOME/.gitconfig file doesn't, and
 - The --global option is used.

Otherwise, write to $HOME/.gitconfig when the --global option is
given, as before.

If the user doesn't create $XDG_CONFIG_HOME/git/config, there is
absolutely no change. Users can use this new file only if they want.

If $XDG_CONFIG_HOME is either not set or empty, $HOME/.config/git/config
will be used.

Advice for users who often come back to an old version of Git: you
shouldn't create this file.

Signed-off-by: Huynh Khoi Nguyen Nguyen <Huynh-Khoi-Nguyen.Nguyen@ensimag.imag.fr>
Signed-off-by: Valentin Duperray <Valentin.Duperray@ensimag.imag.fr>
Signed-off-by: Franck Jonas <Franck.Jonas@ensimag.imag.fr>
Signed-off-by: Lucien Kong <Lucien.Kong@ensimag.imag.fr>
Signed-off-by: Thomas Nguy <Thomas.Nguy@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-config.txt

@@ -97,7 +97,8 @@ OPTIONS
 
 --global::
 	For writing options: write to global ~/.gitconfig file rather than
-	the repository .git/config.
+	the repository .git/config, write to $XDG_CONFIG_HOME/git/config file
+	if this file exists and the ~/.gitconfig file doesn't.
 +
 For reading options: read only from global ~/.gitconfig and from
 $XDG_CONFIG_HOME/git/config rather than from all available files.

builtin/config.c

@@ -387,10 +387,7 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 
 		home_config_paths(&user_config, &xdg_config, "config");
 
-		if (access(user_config, R_OK) && !access(xdg_config, R_OK) &&
-		    (actions == ACTION_LIST ||
-		     actions == ACTION_GET_COLOR ||
-		     actions == ACTION_GET_COLORBOOL))
+		if (access(user_config, R_OK) && !access(xdg_config, R_OK))
 			given_config_file = xdg_config;
 		else if (user_config)
 			given_config_file = user_config;

t/t1306-xdg-files.sh

@@ -125,4 +125,34 @@ test_expect_success 'Checking attributes in a non-XDG global attributes file' '
 '
 
 
+test_expect_success 'write: xdg file exists and ~/.gitconfig doesn'\''t' '
+	mkdir -p "$HOME"/.config/git &&
+	>"$HOME"/.config/git/config &&
+	test_might_fail rm "$HOME"/.gitconfig &&
+	git config --global user.name "write_config" &&
+	echo "[user]" >expected &&
+	echo "	name = write_config" >>expected &&
+	test_cmp expected "$HOME"/.config/git/config
+'
+
+
+test_expect_success 'write: xdg file exists and ~/.gitconfig exists' '
+	>"$HOME"/.gitconfig &&
+	git config --global user.name "write_gitconfig" &&
+	echo "[user]" >expected &&
+	echo "	name = write_gitconfig" >>expected &&
+	test_cmp expected "$HOME"/.gitconfig
+'
+
+
+test_expect_success 'write: ~/.config/git/ exists and config file doesn'\''t' '
+	test_might_fail rm "$HOME"/.gitconfig &&
+	test_might_fail rm "$HOME"/.config/git/config &&
+	git config --global user.name "write_gitconfig" &&
+	echo "[user]" >expected &&
+	echo "	name = write_gitconfig" >>expected &&
+	test_cmp expected "$HOME"/.gitconfig
+'
+
+
 test_done