make URL immutable

it's not really correct that URL is mutable and doesn't do
any argument checking.   propose replacing it with an immutable
named tuple with rich copy-and-mutate methods.

At the moment this makes a hard change to the CreateEnginePlugin
docs that previously recommended url.query.pop().  I can't find
any plugins on github other than my own that are using this
feature, so see if we can just make a hard change on this one.

Fixes: #5526
Change-Id: I28a0a471d80792fa8c28f4fa573d6352966a4a79

1 files changed, 13 insertions, 13 deletions

diff --git a/lib/sqlalchemy/testing/provision.py b/lib/sqlalchemy/testing/provision.py
index 094d1ea94..0edaae490 100644
--- a/lib/sqlalchemy/testing/provision.py
+++ b/lib/sqlalchemy/testing/provision.py
@@ -1,5 +1,4 @@
 import collections
-import copy
 import logging
 
 from . import config
@@ -7,12 +6,14 @@ from . import engines
 from .. import exc
 from ..engine import url as sa_url
 from ..util import compat
-from ..util import parse_qsl
 
 log = logging.getLogger(__name__)
 
 FOLLOWER_IDENT = None
 
+if compat.TYPE_CHECKING:
+    from ..engine import URL
+
 
 class register(object):
     def __init__(self):
@@ -140,7 +141,7 @@ def _generate_driver_urls(url, extra_drivers):
     main_driver = url.get_driver_name()
     extra_drivers.discard(main_driver)
 
-    url = generate_driver_url(url, main_driver, {})
+    url = generate_driver_url(url, main_driver, "")
     yield str(url)
 
     for drv in list(extra_drivers):
@@ -149,12 +150,11 @@ def _generate_driver_urls(url, extra_drivers):
 
             driver_only, query_str = drv.split("?", 1)
 
-            query = parse_qsl(query_str)
         else:
             driver_only = drv
-            query = {}
+            query_str = None
 
-        new_url = generate_driver_url(url, driver_only, query)
+        new_url = generate_driver_url(url, driver_only, query_str)
         if new_url:
             extra_drivers.remove(drv)
 
@@ -162,12 +162,13 @@ def _generate_driver_urls(url, extra_drivers):
 
 
 @register.init
-def generate_driver_url(url, driver, query):
+def generate_driver_url(url, driver, query_str):
+    # type: (URL, str, str) -> URL
     backend = url.get_backend_name()
-    new_url = copy.copy(url)
-    new_url.query = dict(new_url.query)
-    new_url.drivername = "%s+%s" % (backend, driver)
-    new_url.query.update(query)
+
+    new_url = url.set(drivername="%s+%s" % (backend, driver),)
+    new_url = new_url.update_query_string(query_str)
+
     try:
         new_url.get_dialect()
     except exc.NoSuchModuleError:
@@ -236,8 +237,7 @@ def follower_url_from_main(url, ident):
                   database name
     """
     url = sa_url.make_url(url)
-    url.database = ident
-    return url
+    return url.set(database=ident)
 
 
 @register.init