Fix: path.getrelative() gives incorrect results for paths containing "//"

src/host/path_getrelative.c

@@ -8,6 +8,36 @@
 #include <string.h>
 
 
+static void normalize(char* buffer, const char* path)
+{
+	strcpy(buffer, path);
+	do_translate(buffer, '/');
+
+	/* remove any duplicate slashes within the path */
+	char* src = buffer;
+	char* dst = buffer;
+	char last = '\0';
+
+	while (*src != '\0') {
+		/* if I don't have consecutive slashes, keep the char */
+		if (*src != '/' || last != '/') {
+			*(dst++) = *src;
+		}
+
+		/* Allow double-slash at the start of the string, so absolute
+		 * UNC paths can be expressed, but nowhere else */
+		if (src != buffer) {
+			last = (*src);
+		}
+
+		/* check the next one */
+		++src;
+	}
+
+	*dst = '\0';
+}
+
+
 int path_getrelative(lua_State* L)
 {
 	int i, last, count;
@@ -18,10 +48,8 @@ int path_getrelative(lua_State* L)
 	const char* p2 = luaL_checkstring(L, 2);
 
 	/* normalize the paths */
-	strcpy(src, p1);
-	do_translate(src, '/');
-	strcpy(dst, p2);
-	do_translate(dst, '/');
+	normalize(src, p1);
+	normalize(dst, p2);
 
 	/* same directory? */
 	if (strcmp(src, dst) == 0) {

tests/base/test_path.lua

@@ -176,6 +176,14 @@
 		test.isequal("/opt/include", path.getrelative("/home/me/src/project", "/opt/include"))
 	end
 
+	function suite.ignoresExtraSlashes2()
+		test.isequal("..", path.getrelative("/a//b/c","/a/b"))
+	end
+
+	function suite.ignoresExtraSlashes3()
+		test.isequal("..", path.getrelative("/a///b/c","/a/b"))
+	end
+
 
 --
 -- path.isabsolute() tests