create second level deduping when use_labels is turned on

As of #4753 we allow duplicate columns.  This creates some new
problems that there can be duplicate columns in a subquery
which are then not addressible on the outside because they
are ambiguous (Postgresql has this behavior at least).  Additionally
it creates situations where we are making an anon label of an
anon label which is leaking into the query.

New logic for generating anon labels handles this situation and
also alters the .c collection
of a subquery such that we are only getting the first column
from the derived selectable that has that name, the subsequent ones
have a new deduping label with two underscores and are not exposed
in .c.  The dedupe logic when rendering the columns will handle
duplicate label names for different columns, vs. the same column
repeated, as separate cases.

Fixes: #4892
Change-Id: I929fbd8da14bcc239e0481c24bbd9b5ce826e8fa

1 files changed, 11 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 8ee157b6f..b6462b334 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -878,7 +878,13 @@ class ColumnElement(
         while self._is_clone_of is not None:
             self = self._is_clone_of
 
-        return _anonymous_label("%%(%d %s)s" % (id(self), seed or "anon"))
+        # as of 1.4 anonymous label for ColumnElement uses hash(), not id(),
+        # as the identifier, because a column and its annotated version are
+        # the same thing in a SQL statement
+        if isinstance(seed, _anonymous_label):
+            return _anonymous_label("%s%%(%d %s)s" % (seed, hash(self), ""))
+
+        return _anonymous_label("%%(%d %s)s" % (hash(self), seed or "anon"))
 
     @util.memoized_property
     def anon_label(self):
@@ -900,6 +906,10 @@ class ColumnElement(
     def _label_anon_label(self):
         return self._anon_label(getattr(self, "_label", None))
 
+    @util.memoized_property
+    def _dedupe_label_anon_label(self):
+        return self._anon_label(getattr(self, "_label", "anon") + "_")
+
 
 class WrapsColumnExpression(object):
     """Mixin that defines a :class:`.ColumnElement` as a wrapper with special