Infer types in BindParameter when expanding=True

Enhanced the "expanding" feature used for :meth:`_sql.ColumnOperators.in_`
operations to infer the type of expression from the right hand list of
elements, if the left hand side does not have any explicit type set up.
This allows the expression to support stringification among other things.
In 1.3, "expanding" was not automatically used for
:meth:`_sql.ColumnOperators.in_` expressions, so in that sense this change
fixes a behavioral regression.

Fixes: #6222
Change-Id: Icdfda1e2c226a21896cafd6d8f251547794451c2

2 files changed, 25 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index dfa6c0f8f..9e1b69088 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -1392,15 +1392,26 @@ class BindParameter(roles.InElementRole, ColumnElement):
         self.literal_execute = literal_execute
         if _is_crud:
             self._is_crud = True
+
         if type_ is None:
+            if expanding and value:
+                check_value = value[0]
+            else:
+                check_value = value
             if _compared_to_type is not None:
                 self.type = _compared_to_type.coerce_compared_value(
-                    _compared_to_operator, value
+                    _compared_to_operator, check_value
                 )
             else:
-                self.type = type_api._resolve_value_to_type(value)
+                self.type = type_api._resolve_value_to_type(check_value)
         elif isinstance(type_, type):
             self.type = type_()
+        elif type_._is_tuple_type:
+            if expanding and value:
+                check_value = value[0]
+            else:
+                check_value = value
+            self.type = type_._resolve_values_to_types(check_value)
         else:
             self.type = type_
 
diff --git a/lib/sqlalchemy/sql/sqltypes.py b/lib/sqlalchemy/sql/sqltypes.py
index e57a14681..bdfb7d833 100644
--- a/lib/sqlalchemy/sql/sqltypes.py
+++ b/lib/sqlalchemy/sql/sqltypes.py
@@ -2912,8 +2912,20 @@ class TupleType(TypeEngine):
     _is_tuple_type = True
 
     def __init__(self, *types):
+        self._fully_typed = NULLTYPE not in types
         self.types = types
 
+    def _resolve_values_to_types(self, value):
+        if self._fully_typed:
+            return self
+        else:
+            return TupleType(
+                *[
+                    _resolve_value_to_type(elem) if typ is NULLTYPE else typ
+                    for typ, elem in zip(self.types, value)
+                ]
+            )
+
     def result_processor(self, dialect, coltype):
         raise NotImplementedError(
             "The tuple type does not support being fetched "