[GSoC][PATCH 1/3] path.c: Add xdg_cache_home to get paths under XDG_CACHE_HOME

[Devin Lehmacher <lehmacdj@gmail.com>]

This is necessary to make it posible to use XDG_CACHE_HOME for caches in
the XDG standard. I modeled this after the very similar xdg_config_home
function for obtaining paths to functions under XDG_CONFIG_HOME

Signed-off-by: Devin Lehmacher <lehmacdj@gmail.com>
---
 cache.h |  7 +++++++
 path.c  | 15 +++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/cache.h b/cache.h
index 8c0e64420..378a636e1 100644
--- a/cache.h
+++ b/cache.h
@@ -1169,6 +1169,13 @@ extern int is_ntfs_dotgit(const char *name);
  */
 extern char *xdg_config_home(const char *filename);
 
+/**
+ * Return a newly allocated string with the evaluation of
+ * "$XDG_CACHE_HOME/git/$filename" if $XDG_CONFIG_HOME is non-empty, otherwise
+ * "$HOME/.config/git/$filename". Return NULL upon error.
+ */
+extern char *xdg_cache_home(const char *filename);
+
 /* object replacement */
 #define LOOKUP_REPLACE_OBJECT 1
 #define LOOKUP_UNKNOWN_OBJECT 2
diff --git a/path.c b/path.c
index efcedafba..22248436b 100644
--- a/path.c
+++ b/path.c
@@ -1272,6 +1272,21 @@ char *xdg_config_home(const char *filename)
 	return NULL;
 }
 
+char *xdg_cache_home(const char *filename)
+{
+	const char *home, *cache_home;
+
+	assert(filename);
+	cache_home = getenv("XDG_CACHE_HOME");
+	if (cache_home && *cache_home)
+		return mkpathdup("%s/git/%s", cache_home, filename);
+
+	home = getenv("HOME");
+	if (home)
+		return mkpathdup("%s/.cache/git/%s", home, filename);
+	return NULL;
+}
+
 GIT_PATH_FUNC(git_path_cherry_pick_head, "CHERRY_PICK_HEAD")
 GIT_PATH_FUNC(git_path_revert_head, "REVERT_HEAD")
 GIT_PATH_FUNC(git_path_squash_msg, "SQUASH_MSG")
-- 
2.11.0