Let core.excludesfile default to $XDG_CONFIG_HOME/git/ignore

To use the feature of core.excludesfile, the user needs:

 1. to create such a file,

 2. and add configuration variable to point at it.

Instead, we can make this a one-step process by choosing a default value
which points to a filename in the user's $HOME, that is unlikely to
already exist on the system, and only use the presence of the file as a
cue that the user wants to use that feature.

And we use "${XDG_CONFIG_HOME:-$HOME/.config/git}/ignore" as such a
file, in the same directory as the newly added configuration file
("${XDG_CONFIG_HOME:-$HOME/.config/git}/config).  The use of this
directory is in line with XDG specification as a location to store
such application specific files.

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/config.txt

@@ -483,7 +483,9 @@ core.excludesfile::
 	'.git/info/exclude', git looks into this file for patterns
 	of files which are not meant to be tracked.  "`~/`" is expanded
 	to the value of `$HOME` and "`~user/`" to the specified user's
-	home directory.  See linkgit:gitignore[5].
+	home directory. Its default value is $XDG_CONFIG_HOME/git/ignore.
+	If $XDG_CONFIG_HOME is either not set or empty, $HOME/.config/git/ignore
+	is used instead. See linkgit:gitignore[5].
 
 core.askpass::
 	Some commands (e.g. svn and http interfaces) that interactively

Documentation/gitignore.txt

@@ -50,7 +50,9 @@ the repository but are specific to one user's workflow) should go into
 the `$GIT_DIR/info/exclude` file.  Patterns which a user wants git to
 ignore in all situations (e.g., backup or temporary files generated by
 the user's editor of choice) generally go into a file specified by
-`core.excludesfile` in the user's `~/.gitconfig`.
+`core.excludesfile` in the user's `~/.gitconfig`. Its default value is
+$XDG_CONFIG_HOME/git/ignore. If $XDG_CONFIG_HOME is either not set or empty,
+$HOME/.config/git/ignore is used instead.
 
 The underlying git plumbing tools, such as
 'git ls-files' and 'git read-tree', read

dir.c

@@ -1292,12 +1292,17 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 void setup_standard_excludes(struct dir_struct *dir)
 {
 	const char *path;
+	char *xdg_path;
 
 	dir->exclude_per_dir = ".gitignore";
 	path = git_path("info/exclude");
+	if (!excludes_file) {
+		home_config_paths(NULL, &xdg_path, "ignore");
+		excludes_file = xdg_path;
+	}
 	if (!access(path, R_OK))
 		add_excludes_from_file(dir, path);
-	if (excludes_file && !access(excludes_file, R_OK))
+	if (!access(excludes_file, R_OK))
 		add_excludes_from_file(dir, excludes_file);
 }
 

t/t1306-xdg-files.sh

@@ -67,4 +67,33 @@ test_expect_success 'read with --list: xdg file exists and ~/.gitconfig exists'
 '
 
 
+test_expect_success 'Setup' '
+	git init git &&
+	cd git &&
+	echo foo >to_be_excluded
+'
+
+
+test_expect_success 'Exclusion of a file in the XDG ignore file' '
+	mkdir -p "$HOME"/.config/git/ &&
+	echo to_be_excluded >"$HOME"/.config/git/ignore &&
+	test_must_fail git add to_be_excluded
+'
+
+
+test_expect_success 'Exclusion in both XDG and local ignore files' '
+	echo to_be_excluded >.gitignore &&
+	test_must_fail git add to_be_excluded
+'
+
+
+test_expect_success 'Exclusion in a non-XDG global ignore file' '
+	rm .gitignore &&
+	echo >"$HOME"/.config/git/ignore &&
+	echo to_be_excluded >"$HOME"/my_gitignore &&
+	git config core.excludesfile "$HOME"/my_gitignore &&
+	test_must_fail git add to_be_excluded
+'
+
+
 test_done