bpo-39799: Never return base's fragment from urllib.parse.urljoin

Lib/test/test_urlparse.py

@@ -396,7 +396,6 @@ def test_RFC1808(self):
         self.checkJoin(RFC1808_BASE, '../../g', 'http://a/g')
 
         # "abnormal" cases from RFC 1808:
-        self.checkJoin(RFC1808_BASE, '', 'http://a/b/c/d;p?q#f')
         self.checkJoin(RFC1808_BASE, 'g.', 'http://a/b/c/g.')
         self.checkJoin(RFC1808_BASE, '.g', 'http://a/b/c/.g')
         self.checkJoin(RFC1808_BASE, 'g..', 'http://a/b/c/g..')
@@ -412,6 +411,7 @@ def test_RFC1808(self):
         #self.checkJoin(RFC1808_BASE, 'http:', 'http:')
 
         # XXX: The following tests are no longer compatible with RFC3986
+        # self.checkJoin(RFC1808_BASE, '', 'http://a/b/c/d;p?q#f')
         # self.checkJoin(RFC1808_BASE, '../../../g', 'http://a/../g')
         # self.checkJoin(RFC1808_BASE, '../../../../g', 'http://a/../../g')
         # self.checkJoin(RFC1808_BASE, '/./g', 'http://a/./g')
@@ -525,6 +525,10 @@ def test_RFC3986(self):
         # Test for issue9721
         self.checkJoin('http://a/b/c/de', ';x','http://a/b/c/;x')
 
+        # Tests for issue39799: no base fragment
+        self.checkJoin('http://a/b#f', '', 'http://a/b')
+        self.checkJoin('http://a/b/#f', 'g', 'http://a/b/g')
+
     def test_urljoins(self):
         self.checkJoin(SIMPLE_BASE, 'g:h','g:h')
         self.checkJoin(SIMPLE_BASE, 'g','http://a/b/c/g')

Lib/urllib/parse.py

@@ -566,8 +566,6 @@ def urljoin(base, url, allow_fragments=True):
     interpretation of the latter."""
     if not base:
         return url
-    if not url:
-        return base
 
     base, url, _coerce_result = _coerce_args(base, url)
     bscheme, bnetloc, bpath, bquery, bfragment = \

Misc/NEWS.d/next/Library/2020-02-29-20-44-36.bpo-39799.qTHOaP.rst

@@ -0,0 +1,2 @@
+Fix ``urllib.parse.urljoin``.
+In RFC 3986, ``base``'s fragment is always discarded.