Revert "[3.8] bpo-27657: Fix urlparse() with numeric paths (GH-16839)" (GH-18525)

This reverts commit 0f3187c1ce.

The change broke the backwards compatibility of parsing behavior in a
patch release of Python (3.8.1). A decision was taken to revert this
patch in 3.8.2.

In https://bugs.python.org/issue27657 it was decided that the previous
behavior like

>>> urlparse('localhost:8080')
ParseResult(scheme='', netloc='', path='localhost:8080', params='', query='', fragment='')

>>> urlparse('undefined:8080')
ParseResult(scheme='', netloc='', path='undefined:8080', params='', query='', fragment='')

needs to be preserved in patch releases as number of users rely upon it.

Explicitly mention the releases involved with the revert in NEWS.
Adopt the wording suggested by @ned-deily.

Lib/test/test_urlparse.py

@@ -709,17 +709,15 @@ class UrlParseTestCase(unittest.TestCase):
 
     def test_portseparator(self):
         # Issue 754016 makes changes for port separator ':' from scheme separator
-        self.assertEqual(urllib.parse.urlparse("http:80"), ('http','','80','','',''))
+        self.assertEqual(urllib.parse.urlparse("path:80"),
-        self.assertEqual(urllib.parse.urlparse("https:80"), ('https','','80','','',''))
+                ('','','path:80','','',''))
-        self.assertEqual(urllib.parse.urlparse("path:80"), ('path','','80','','',''))
         self.assertEqual(urllib.parse.urlparse("http:"),('http','','','','',''))
         self.assertEqual(urllib.parse.urlparse("https:"),('https','','','','',''))
         self.assertEqual(urllib.parse.urlparse("http://www.python.org:80"),
                 ('http','www.python.org:80','','','',''))
         # As usual, need to check bytes input as well
-        self.assertEqual(urllib.parse.urlparse(b"http:80"), (b'http',b'',b'80',b'',b'',b''))
+        self.assertEqual(urllib.parse.urlparse(b"path:80"),
-        self.assertEqual(urllib.parse.urlparse(b"https:80"), (b'https',b'',b'80',b'',b'',b''))
+                (b'',b'',b'path:80',b'',b'',b''))
-        self.assertEqual(urllib.parse.urlparse(b"path:80"), (b'path',b'',b'80',b'',b'',b''))
         self.assertEqual(urllib.parse.urlparse(b"http:"),(b'http',b'',b'',b'',b'',b''))
         self.assertEqual(urllib.parse.urlparse(b"https:"),(b'https',b'',b'',b'',b'',b''))
         self.assertEqual(urllib.parse.urlparse(b"http://www.python.org:80"),

Lib/urllib/parse.py

@@ -431,11 +431,31 @@ def urlsplit(url, scheme='', allow_fragments=True):
     netloc = query = fragment = ''
     i = url.find(':')
     if i > 0:
+        if url[:i] == 'http': # optimize the common case
+            url = url[i+1:]
+            if url[:2] == '//':
+                netloc, url = _splitnetloc(url, 2)
+                if (('[' in netloc and ']' not in netloc) or
+                        (']' in netloc and '[' not in netloc)):
+                    raise ValueError("Invalid IPv6 URL")
+            if allow_fragments and '#' in url:
+                url, fragment = url.split('#', 1)
+            if '?' in url:
+                url, query = url.split('?', 1)
+            _checknetloc(netloc)
+            v = SplitResult('http', netloc, url, query, fragment)
+            _parse_cache[key] = v
+            return _coerce_result(v)
         for c in url[:i]:
             if c not in scheme_chars:
                 break
         else:
-            scheme, url = url[:i].lower(), url[i+1:]
+            # make sure "url" is not actually a port number (in which case
+            # "scheme" is really part of the path)
+            rest = url[i+1:]
+            if not rest or any(c not in '0123456789' for c in rest):
+                # not a port number
+                scheme, url = url[:i].lower(), rest
 
     if url[:2] == '//':
         netloc, url = _splitnetloc(url, 2)

Misc/NEWS.d/next/Library/2020-02-16-07-08-54.bpo-27657.9atgcz.rst

@@ -0,0 +1,5 @@
+The original fix for bpo-27657, "Fix urlparse() with numeric paths" (GH-16839)
+included in 3.8.1, inadvertently introduced a behavior change that broke
+several third-party packages relying on the original undefined parsing
+behavior. The change is reverted in 3.8.2, restoring the behavior of 3.8.0 and
+earlier releases.