URL: protocol setter and special URLs (#4413)

* URL: protocol setter and special URLs

Closes whatwg/url#104.

Author: annevk

url/setters_tests.json

@@ -102,14 +102,30 @@
             }
         },
         {
-            "comment": "Can’t switch from special scheme to non-special. Note: this may change, see https://github.com/whatwg/url/issues/104",
+            "comment": "Can’t switch from special scheme to non-special",
             "href": "http://example.net",
             "new_value": "b",
             "expected": {
                 "href": "http://example.net/",
                 "protocol": "http:"
             }
         },
+        {
+            "href": "https://example.net",
+            "new_value": "s",
+            "expected": {
+                "href": "https://example.net/",
+                "protocol": "https:"
+            }
+        },
+        {
+            "href": "ftp://example.net",
+            "new_value": "test",
+            "expected": {
+                "href": "ftp://example.net/",
+                "protocol": "ftp:"
+            }
+        },
         {
             "comment": "Cannot-be-a-base URL doesn’t have a host, but URL in a special scheme must.",
             "href": "mailto:[email protected]",
@@ -120,14 +136,38 @@
             }
         },
         {
-            "comment": "Can’t switch from non-special scheme to special. Note: this may change, see https://github.com/whatwg/url/issues/104",
+            "comment": "Can’t switch from non-special scheme to special",
             "href": "ssh://[email protected]",
             "new_value": "http",
             "expected": {
                 "href": "ssh://[email protected]/",
                 "protocol": "ssh:"
             }
         },
+        {
+            "href": "ssh://[email protected]",
+            "new_value": "gopher",
+            "expected": {
+                "href": "ssh://[email protected]/",
+                "protocol": "ssh:"
+            }
+        },
+        {
+            "href": "ssh://[email protected]",
+            "new_value": "file",
+            "expected": {
+                "href": "ssh://[email protected]/",
+                "protocol": "ssh:"
+            }
+        },
+        {
+            "href": "nonsense:///test",
+            "new_value": "https",
+            "expected": {
+                "href": "nonsense:///test",
+                "protocol": "nonsense:"
+            }
+        },
         {
             "comment": "Stuff after the first ':' is ignored",
             "href": "http://example.net",