Fix DSN parsing regression

1d650ed broke certain cases of DSN parsing, fix that.

asyncpg/__init__.py

@@ -31,4 +31,4 @@
 #    snapshots will automatically include the git revision
 #    in __version__, for example: '0.16.0.dev0+ge06ad03'
 
-__version__ = '0.18.0'
+__version__ = '0.18.1'

asyncpg/connect_utils.py

@@ -215,7 +215,8 @@ def _parse_connect_dsn_and_args(*, dsn, host, port, user,
             else:
                 hostspec = parsed.netloc
 
-            host, port = _parse_hostlist(hostspec, port)
+            if hostspec:
+                host, port = _parse_hostlist(hostspec, port)
 
         if parsed.path and database is None:
             database = parsed.path
@@ -234,16 +235,16 @@ def _parse_connect_dsn_and_args(*, dsn, host, port, user,
                 if isinstance(val, list):
                     query[key] = val[-1]
 
-            if 'host' in query:
-                val = query.pop('host')
-                if not host and val:
-                    host, port = _parse_hostlist(val, port)
-
             if 'port' in query:
                 val = query.pop('port')
                 if not port and val:
                     port = [int(p) for p in val.split(',')]
 
+            if 'host' in query:
+                val = query.pop('host')
+                if not host and val:
+                    host, port = _parse_hostlist(val, port)
+
             if 'dbname' in query:
                 val = query.pop('dbname')
                 if database is None:

tests/test_connect.py

@@ -392,6 +392,16 @@ class TestConnectParams(tb.TestCase):
                 'could not match 2 port numbers to 3 hosts'
             )
         },
+        {
+            'dsn': 'postgres://user@?port=56226&host=%2Ftmp',
+            'result': (
+                [os.path.join('/tmp', '.s.PGSQL.56226')],
+                {
+                    'user': 'user',
+                    'database': 'user',
+                }
+            )
+        },
     ]
 
     @contextlib.contextmanager