Spec update: make non-special URLs idempotent

Follows whatwg/url#505.

README.md

@@ -4,7 +4,7 @@ whatwg-url is a full implementation of the WHATWG [URL Standard](https://url.spe
 
 ## Specification conformance
 
-whatwg-url is currently up to date with the URL spec up to commit [975614e](https://github.com/whatwg/url/commit/975614edeee28628298d39af174e9a276366de4f).
+whatwg-url is currently up to date with the URL spec up to commit [83adf0c](https://github.com/whatwg/url/commit/83adf0c9ca9a88948e1e5d93374ffded04eec727).
 
 For `file:` URLs, whose [origin is left unspecified](https://url.spec.whatwg.org/#concept-url-origin), whatwg-url chooses to use a new opaque origin (which serializes to `"null"`).
 

scripts/get-latest-platform-tests.js

@@ -24,7 +24,7 @@ process.on("unhandledRejection", err => {
 // 1. Go to https://github.com/w3c/web-platform-tests/tree/master/url
 // 2. Press "y" on your keyboard to get a permalink
 // 3. Copy the commit hash
-const commitHash = "6c74b7e43c9a1f6dc3dc529e427e2ef96152409e";
+const commitHash = "551c9d604fb8b97d3f8c65793bb047d15baddbc2";
 
 const urlPrefix = `https://raw.githubusercontent.com/web-platform-tests/wpt/${commitHash}/url/`;
 const targetDir = path.resolve(__dirname, "..", "test", "web-platform-tests");

src/url-state-machine.js

@@ -1113,8 +1113,11 @@ function serializeURL(url, excludeFragment) {
   if (url.cannotBeABaseURL) {
     output += url.path[0];
   } else {
-    for (const string of url.path) {
-      output += "/" + string;
+    if (url.host === null && url.path.length > 1 && url.path[0] === "") {
+      output += "/.";
+    }
+    for (const segment of url.path) {
+      output += "/" + segment;
     }
   }