- improve overlapping selectables, apply to both query and relationship

- clean up inspect() calls within query._join()
- make sure join.alias(flat) propagates
- fix almost all assertion tests

2 files changed, 20 insertions, 6 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 633a3ddba..e7ef3cb72 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -4001,7 +4001,8 @@ class Join(FromClause):
         """
         if flat:
             assert name is None, "Can't send name argument with flat"
-            left_a, right_a = self.left.alias(), self.right.alias()
+            left_a, right_a = self.left.alias(flat=True), \
+                                self.right.alias(flat=True)
             adapter = sqlutil.ClauseAdapter(left_a).\
                         chain(sqlutil.ClauseAdapter(right_a))
 
diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index c80693706..6f4d27e1b 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -200,15 +200,28 @@ def clause_is_present(clause, search):
 
     """
 
-    stack = [search]
-    while stack:
-        elem = stack.pop()
+    for elem in surface_selectables(search):
         if clause == elem:  # use == here so that Annotated's compare
             return True
-        elif isinstance(elem, expression.Join):
+    else:
+        return False
+
+def surface_selectables(clause):
+    stack = [clause]
+    while stack:
+        elem = stack.pop()
+        yield elem
+        if isinstance(elem, expression.Join):
             stack.extend((elem.left, elem.right))
-    return False
 
+def selectables_overlap(left, right):
+    """Return True if left/right have some overlapping selectable"""
+
+    return bool(
+                set(surface_selectables(left)).intersection(
+                        surface_selectables(right)
+                    )
+            )
 
 def bind_values(clause):
     """Return an ordered list of "bound" values in the given clause.