establish mypy / typing approach for v2.0

large patch to get ORM / typing efforts started.
this is to support adding new test cases to mypy,
support dropping sqlalchemy2-stubs entirely from the
test suite, validate major ORM typing reorganization
to eliminate the need for the mypy plugin.

* New declarative approach which uses annotation
  introspection, fixes: #7535
* Mapped[] is now at the base of all ORM constructs
  that find themselves in classes, to support direct
  typing without plugins
* Mypy plugin updated for new typing structures
* Mypy test suite broken out into "plugin" tests vs.
  "plain" tests, and enhanced to better support test
  structures where we assert that various objects are
  introspected by the type checker as we expect.
  as we go forward with typing, we will
  add new use cases to "plain" where we can assert that
  types are introspected as we expect.
* For typing support, users will be much more exposed to the
  class names of things.  Add these all to "sqlalchemy" import
  space.
* Column(ForeignKey()) no longer needs to be `@declared_attr`
  if the FK refers to a remote table
* composite() attributes mapped to a dataclass no longer
  need to implement a `__composite_values__()` method
* with_variant() accepts multiple dialect names

Change-Id: I22797c0be73a8fbbd2d6f5e0c0b7258b17fe145d
Fixes: #7535
Fixes: #7551
References: #6810

1 files changed, 37 insertions, 3 deletions

diff --git a/lib/sqlalchemy/ext/mypy/infer.py b/lib/sqlalchemy/ext/mypy/infer.py
index 3cd946e04..6a5e99e48 100644
--- a/lib/sqlalchemy/ext/mypy/infer.py
+++ b/lib/sqlalchemy/ext/mypy/infer.py
@@ -42,11 +42,13 @@ def infer_type_from_right_hand_nameexpr(
     left_hand_explicit_type: Optional[ProperType],
     infer_from_right_side: RefExpr,
 ) -> Optional[ProperType]:
-
     type_id = names.type_id_for_callee(infer_from_right_side)
-
     if type_id is None:
         return None
+    elif type_id is names.MAPPED:
+        python_type_for_type = _infer_type_from_mapped(
+            api, stmt, node, left_hand_explicit_type, infer_from_right_side
+        )
     elif type_id is names.COLUMN:
         python_type_for_type = _infer_type_from_decl_column(
             api, stmt, node, left_hand_explicit_type
@@ -245,7 +247,7 @@ def _infer_type_from_decl_composite_property(
     node: Var,
     left_hand_explicit_type: Optional[ProperType],
 ) -> Optional[ProperType]:
-    """Infer the type of mapping from a CompositeProperty."""
+    """Infer the type of mapping from a Composite."""
 
     assert isinstance(stmt.rvalue, CallExpr)
     target_cls_arg = stmt.rvalue.args[0]
@@ -271,6 +273,38 @@ def _infer_type_from_decl_composite_property(
         return python_type_for_type
 
 
+def _infer_type_from_mapped(
+    api: SemanticAnalyzerPluginInterface,
+    stmt: AssignmentStmt,
+    node: Var,
+    left_hand_explicit_type: Optional[ProperType],
+    infer_from_right_side: RefExpr,
+) -> Optional[ProperType]:
+    """Infer the type of mapping from a right side expression
+    that returns Mapped.
+
+
+    """
+    assert isinstance(stmt.rvalue, CallExpr)
+
+    # (Pdb) print(stmt.rvalue.callee)
+    # NameExpr(query_expression [sqlalchemy.orm._orm_constructors.query_expression])  # noqa: E501
+    # (Pdb) stmt.rvalue.callee.node
+    # <mypy.nodes.FuncDef object at 0x7f8d92fb5940>
+    # (Pdb) stmt.rvalue.callee.node.type
+    # def [_T] (default_expr: sqlalchemy.sql.elements.ColumnElement[_T`-1] =) -> sqlalchemy.orm.base.Mapped[_T`-1]  # noqa: E501
+    # sqlalchemy.orm.base.Mapped[_T`-1]
+    # the_mapped_type = stmt.rvalue.callee.node.type.ret_type
+
+    # TODO: look at generic ref and either use that,
+    # or reconcile w/ what's present, etc.
+    the_mapped_type = util.type_for_callee(infer_from_right_side)  # noqa
+
+    return infer_type_from_left_hand_type_only(
+        api, node, left_hand_explicit_type
+    )
+
+
 def _infer_type_from_decl_column_property(
     api: SemanticAnalyzerPluginInterface,
     stmt: AssignmentStmt,