Support expanding $XDG_CONFIG_HOME in user config paths

If ~/.config is specified as a prefix to a configured path,
then it is expanded to the $XDG_CONFIG_HOME if that exists

Add --with-user-config ./configure option to configure a
different user config directory.

Interpolate the right directories into documentation.

2 files changed, 30 insertions, 13 deletions

diff --git a/common/path.c b/common/path.c
index d807301..a22c2a6 100644
--- a/common/path.c
+++ b/common/path.c
@@ -91,19 +91,40 @@ p11_path_base (const char *path)
 	return strndup (beg, end - beg);
 }
 
+static inline bool
+is_path_component_or_null (char ch)
+{
+	return (ch == '\0' || ch == '/'
+#ifdef OS_WIN32
+			|| ch == '\\'
+#endif
+		);
+}
+
 static char *
 expand_homedir (const char *remainder)
 {
 	const char *env;
 
-	if (remainder[0] == '\0')
-		remainder = NULL;
-
 	if (getauxval (AT_SECURE)) {
 		errno = EPERM;
 		return NULL;
 	}
 
+	while (remainder[0] && is_path_component_or_null (remainder[0]))
+		remainder++;
+	if (remainder[0] == '\0')
+		remainder = NULL;
+
+	/* Expand $XDG_CONFIG_HOME */
+	if (remainder != NULL &&
+	    strncmp (remainder, ".config", 7) == 0 &&
+	    is_path_component_or_null (remainder[7])) {
+		env = getenv ("XDG_CONFIG_HOME");
+		if (env && env[0])
+			return p11_path_build (env, remainder + 8, NULL);
+	}
+
 	env = getenv ("HOME");
 	if (env && env[0]) {
 		return p11_path_build (env, remainder, NULL);
@@ -139,16 +160,6 @@ expand_homedir (const char *remainder)
 	}
 }
 
-static inline bool
-is_path_component_or_null (char ch)
-{
-	return (ch == '\0' || ch == '/'
-#ifdef OS_WIN32
-			|| ch == '\\'
-#endif
-		);
-}
-
 char *
 p11_path_expand (const char *path)
 {
diff --git a/common/tests/test-path.c b/common/tests/test-path.c
index 0077cd0..a6ba54d 100644
--- a/common/tests/test-path.c
+++ b/common/tests/test-path.c
@@ -117,6 +117,12 @@ test_expand (void)
 	                       p11_path_expand ("~/my/path"));
 	check_equals_and_free ("/home/blah",
 	                       p11_path_expand ("~"));
+	putenv ("XDG_CONFIG_HOME=/my");
+	check_equals_and_free ("/my/path",
+	                       p11_path_expand ("~/.config/path"));
+	putenv ("XDG_CONFIG_HOME=");
+	check_equals_and_free ("/home/blah/.config/path",
+	                       p11_path_expand ("~/.config/path"));
 #else /* OS_WIN32 */
 	putenv ("HOME=C:\\Users\\blah");
 	check_equals_and_free ("C:\\Users\\blah\\path",