Allow "assignments" like self.foo: int

Although this is an assignment in the Python AST, there is no value being assigned.

Author: knutwannheden

rewrite/rewrite/python/_parser_visitor.py

@@ -102,7 +102,7 @@ def visit_arguments(self, node, with_close_paren: bool = True) -> List[JRightPad
             if not node.vararg:
                 empty_name = j.VariableDeclarations.NamedVariable(random_id(), Space.EMPTY, Markers.EMPTY,
                                                                   cast(j.Identifier, self.__convert_name('', None)), [],
-                                                                  None, None, None)
+                                                                  None, None)
                 kwonly_prefix = self.__source_before('*')
                 mapped.append(
                     JRightPadded(
@@ -308,6 +308,24 @@ def visit_AnnAssign(self, node):
                 ) if node.value else None,
                 self.__map_type(node)
             )
+        elif not node.value:
+            return py.ExpressionStatement(
+                random_id(),
+                py.TypeHintedExpression(
+                    random_id(),
+                    prefix,
+                    Markers.EMPTY,
+                    self.__convert(node.target),
+                    py.TypeHint(
+                        random_id(),
+                        self.__source_before(':'),
+                        Markers.EMPTY,
+                        self.__convert_type(node.annotation),
+                        self.__map_type(node.annotation)
+                    ),
+                    self.__map_type(node)
+                )
+            )
         else:
             name = cast(j.Identifier, self.__convert(node.target))
             if node.annotation:

rewrite/tests/python/all/class_test.py

@@ -25,6 +25,19 @@ class Foo:
     )
 
 
+def test_typed_field():
+    # language=python
+    rewrite_run(
+        python(
+            """\
+            class Foo:
+                def __init__(self):
+                    self.target: int
+            """
+        )
+    )
+
+
 def test_enum():
     # language=python
     rewrite_run(