Preserve empty relative paths during normalization

src/hyperlink/_url.py

@@ -1469,7 +1469,8 @@ def normalize(
         * Uppercase remaining percent-encoded octets (`RFC 3986 2.1`_)
         * Convert scheme and host casing to lowercase (`RFC 3986 3.2.2`_)
         * Resolve any "." and ".." references in the path (`RFC 3986 6.2.2.3`_)
-        * Ensure an ending slash on URLs with an empty path (`RFC 3986 6.2.3`_)
+        * Ensure an ending slash on URLs with a host and an empty path
+          (`RFC 3986 6.2.3`_)
         * Encode any stray percent signs (`%`) in percent-encoded
           fields (path, query, fragment, userinfo) (`RFC 3986 2.4`_)
 
@@ -1515,7 +1516,7 @@ def _dec_unres(target):
                 kw["path"] = [
                     _dec_unres(p) for p in _resolve_dot_segments(self.path)
                 ]
-            else:
+            elif self.host:
                 kw["path"] = (u"",)
         if query:
             kw["query"] = [

src/hyperlink/test/test_decoded_url.py

@@ -15,6 +15,20 @@
 
 
 class TestURL(HyperlinkTestCase):
+    def test_normalize_empty_relative_path(self):
+        # type: () -> None
+        base = DecodedURL.from_text("http://example.com/a/b?old=1")
+        for text in ("", "?x=1", "#section", "?x=1#section"):
+            reference = DecodedURL.from_text(text)
+            normalized = reference.normalize()
+            assert normalized.path == ()
+            assert not normalized.rooted
+            assert normalized.to_text() == text
+            assert base.click(normalized.to_text()) == base.click(text)
+            assert base.encoded_url.click(normalized.encoded_url) == (
+                base.encoded_url.click(reference.encoded_url)
+            )
+
     def test_durl_basic(self):
         # type: () -> None
         bdurl = DecodedURL.from_text(BASIC_URL)

src/hyperlink/test/test_url.py

@@ -1461,6 +1461,18 @@ def test_normalize(self):
             == "ftp://%25:%25@/%25%25%25/%25a%25b?%25=%25%25#%25"
         )
 
+    def test_normalize_empty_relative_path(self):
+        # type: () -> None
+        base = URL.from_text("http://example.com/a/b?old=1")
+        for text in ("", "?x=1", "#section", "?x=1#section"):
+            reference = URL.from_text(text)
+            normalized = reference.normalize()
+            assert normalized.path == ()
+            assert not normalized.rooted
+            assert normalized.to_text() == text
+            assert base.click(normalized) == base.click(reference)
+            assert normalized.normalize() == normalized
+
     def test_str(self):
         # type: () -> None