Fold entities into existing joins when resolving FROM ambiguity

Fixed 1.3 regression in new "ambiguous FROMs" query logic introduced in
:ref:`change_4365` where a :class:`.Query` that explicitly places an entity
in the FROM clause with :meth:`.Query.select_from` and also joins to it
using :meth:`.Query.join` would later cause an "ambiguous FROM" error if
that entity were used in additional joins, as the entity appears twice in
the "from" list of the :class:`.Query`.  The fix resolves this ambiguity by
folding the standalone entity into the join that it's already a part of in
the same way that ultimately happens when the SELECT statement is rendered.

Fixes: #4584
Change-Id: Ic62ca09c6d329695b21ed4f1be8621edcbb18e19

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index 3077840c6..8719b26ec 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -20,6 +20,7 @@ from .annotation import _shallow_annotate  # noqa
 from .base import _from_objects
 from .base import ColumnSet
 from .ddl import sort_tables  # noqa
+from .elements import _expand_cloned
 from .elements import _find_columns  # noqa
 from .elements import _label_reference
 from .elements import _textual_label_reference
@@ -149,6 +150,16 @@ def find_left_clause_to_join_from(clauses, join_to, onclause):
                 idx.append(i)
                 break
 
+    if len(idx) > 1:
+        # this is the same "hide froms" logic from
+        # Selectable._get_display_froms
+        toremove = set(
+            chain(*[_expand_cloned(f._hide_froms) for f in clauses])
+        )
+        idx = [
+            i for i in idx if clauses[i] not in toremove
+        ]
+
     # onclause was given and none of them resolved, so assume
     # all indexes can match
     if not idx and onclause is not None: