Use inheritance to allow most TypeVisitors not to deal with "syntheti…

…c" types

This is a nearly-complete fix to python#730 --
the trick is that some types aren't real, they're synthetic AST constructs, and
so we shouldn't have to deal with those in every type visitor. Only the type
visitors that deal with types before the synthetic constructs are analyzed away.

mypy/erasetype.py

@@ -26,10 +26,8 @@ def erase_type(typ: Type) -> Type:
 
 
 class EraseTypeVisitor(TypeVisitor[Type]):
-    def visit_unbound_type(self, t: UnboundType) -> Type:
-        assert False, 'Not supported'
 
-    def visit_type_list(self, t: TypeList) -> Type:
+    def visit_unbound_type(self, t: UnboundType) -> Type:
         assert False, 'Not supported'
 
     def visit_any(self, t: AnyType) -> Type:

mypy/expandtype.py

@@ -63,9 +63,6 @@ def __init__(self, variables: Mapping[TypeVarId, Type]) -> None:
     def visit_unbound_type(self, t: UnboundType) -> Type:
         return t
 
-    def visit_type_list(self, t: TypeList) -> Type:
-        assert False, 'Not supported'
-
     def visit_any(self, t: AnyType) -> Type:
         return t
 

mypy/fixup.py

@@ -177,9 +177,6 @@ def visit_callable_type(self, ct: CallableType) -> None:
                     val.accept(self)
             v.upper_bound.accept(self)
 
-    def visit_ellipsis_type(self, e: EllipsisType) -> None:
-        pass  # Nothing to descend into.
-
     def visit_overloaded(self, t: Overloaded) -> None:
         for ct in t.items():
             ct.accept(self)
@@ -210,10 +207,6 @@ def visit_typeddict_type(self, tdt: TypedDictType) -> None:
         if tdt.fallback is not None:
             tdt.fallback.accept(self)
 
-    def visit_type_list(self, tl: TypeList) -> None:
-        for t in tl.items:
-            t.accept(self)
-
     def visit_type_var(self, tvt: TypeVarType) -> None:
         if tvt.values:
             for vt in tvt.values:

mypy/indirection.py

@@ -2,7 +2,7 @@
 from abc import abstractmethod
 
 from mypy.visitor import NodeVisitor
-from mypy.types import TypeVisitor
+from mypy.types import SyntheticTypeVisitor
 from mypy.nodes import MODULE_REF
 import mypy.nodes as nodes
 import mypy.types as types
@@ -19,7 +19,7 @@ def extract_module_names(type_name: Optional[str]) -> List[str]:
         return []
 
 
-class TypeIndirectionVisitor(TypeVisitor[Set[str]]):
+class TypeIndirectionVisitor(SyntheticTypeVisitor[Set[str]]):
     """Returns all module references within a particular type."""
 
     def __init__(self) -> None:

mypy/join.py

@@ -107,9 +107,6 @@ def visit_union_type(self, t: UnionType) -> Type:
         else:
             return UnionType.make_simplified_union([self.s, t])
 
-    def visit_type_list(self, t: TypeList) -> Type:
-        assert False, 'Not supported'
-
     def visit_any(self, t: AnyType) -> Type:
         return t
 

mypy/meet.py

@@ -139,9 +139,6 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
         else:
             return AnyType()
 
-    def visit_type_list(self, t: TypeList) -> Type:
-        assert False, 'Not supported'
-
     def visit_any(self, t: AnyType) -> Type:
         return self.s
 

mypy/sametypes.py

@@ -55,9 +55,6 @@ def __init__(self, right: Type) -> None:
     def visit_unbound_type(self, left: UnboundType) -> bool:
         return True
 
-    def visit_type_list(self, t: TypeList) -> bool:
-        assert False, 'Not supported'
-
     def visit_any(self, left: AnyType) -> bool:
         return isinstance(self.right, AnyType)
 

mypy/server/astdiff.py

@@ -136,9 +136,6 @@ def __init__(self, right: Type) -> None:
     def visit_unbound_type(self, left: UnboundType) -> bool:
         return False
 
-    def visit_type_list(self, t: TypeList) -> bool:
-        assert False, 'Not supported'
-
     def visit_any(self, left: AnyType) -> bool:
         return isinstance(self.right, AnyType)
 

mypy/subtypes.py

@@ -109,9 +109,6 @@ def __init__(self, right: Type,
     def visit_unbound_type(self, left: UnboundType) -> bool:
         return True
 
-    def visit_type_list(self, t: TypeList) -> bool:
-        assert False, 'Not supported'
-
     def visit_any(self, left: AnyType) -> bool:
         return True
 
@@ -563,9 +560,6 @@ def visit_unbound_type(self, left: UnboundType) -> bool:
         # from unions, which could filter out some bogus messages.
         return True
 
-    def visit_type_list(self, left: TypeList) -> bool:
-        assert False, 'Should not happen'
-
     def visit_any(self, left: AnyType) -> bool:
         return isinstance(self.right, AnyType)
 

mypy/types.py

@@ -975,6 +975,7 @@ def __init__(self, type: Type, line: int = -1, column: int = -1) -> None:
         super().__init__(line, column)
 
     def accept(self, visitor: 'TypeVisitor[T]') -> T:
+        assert isinstance(visitor, SyntheticTypeVisitor)
         return visitor.visit_star_type(self)
 
 
@@ -1116,6 +1117,7 @@ class EllipsisType(Type):
     """
 
     def accept(self, visitor: 'TypeVisitor[T]') -> T:
+        assert isinstance(visitor, SyntheticTypeVisitor)
         return visitor.visit_ellipsis_type(self)
 
     def serialize(self) -> JsonDict:
@@ -1199,9 +1201,6 @@ def _notimplemented_helper(self, name: str) -> NotImplementedError:
     def visit_unbound_type(self, t: UnboundType) -> T:
         pass
 
-    def visit_type_list(self, t: TypeList) -> T:
-        raise self._notimplemented_helper('type_list')
-
     @abstractmethod
     def visit_any(self, t: AnyType) -> T:
         pass
@@ -1244,9 +1243,6 @@ def visit_tuple_type(self, t: TupleType) -> T:
     def visit_typeddict_type(self, t: TypedDictType) -> T:
         pass
 
-    def visit_star_type(self, t: StarType) -> T:
-        raise self._notimplemented_helper('star_type')
-
     @abstractmethod
     def visit_union_type(self, t: UnionType) -> T:
         pass
@@ -1255,15 +1251,34 @@ def visit_union_type(self, t: UnionType) -> T:
     def visit_partial_type(self, t: PartialType) -> T:
         pass
 
-    def visit_ellipsis_type(self, t: EllipsisType) -> T:
-        raise self._notimplemented_helper('ellipsis_type')
-
     @abstractmethod
     def visit_type_type(self, t: TypeType) -> T:
         pass
 
 
-class TypeTranslator(TypeVisitor[Type]):
+class SyntheticTypeVisitor(TypeVisitor[T]):
+    """A TypeVisitor that also knows how to visit synthetic AST constructs.
+
+       Not just real types."""
+
+    @abstractmethod
+    def visit_star_type(self, t: StarType) -> T:
+        pass
+
+    @abstractmethod
+    def visit_type_list(self, t: TypeList) -> T:
+        pass
+
+    @abstractmethod
+    def visit_callable_argument(self, t: CallableArgument) -> T:
+        pass
+
+    @abstractmethod
+    def visit_ellipsis_type(self, t: EllipsisType) -> T:
+        pass
+
+
+class TypeTranslator(SyntheticTypeVisitor[Type]):
     """Identity type transformation.
 
     Subclass this and override some methods to implement a non-trivial
@@ -1351,7 +1366,7 @@ def visit_type_type(self, t: TypeType) -> Type:
         return TypeType(t.item.accept(self), line=t.line, column=t.column)
 
 
-class TypeStrVisitor(TypeVisitor[str]):
+class TypeStrVisitor(SyntheticTypeVisitor[str]):
     """Visitor for pretty-printing types into strings.
 
     This is mostly for debugging/testing.
@@ -1510,7 +1525,7 @@ def keywords_str(self, a: Iterable[Tuple[str, Type]]) -> str:
         ])
 
 
-class TypeQuery(Generic[T], TypeVisitor[T]):
+class TypeQuery(SyntheticTypeVisitor[T]):
     """Visitor for performing queries of types.
 
     strategy is used to combine results for a series of types