Make TypeVisitor and SyntheticTypeVisitor (almost) fully abstract (#7312

)

This pull request almost resolves #730 -- it makes all TypeVisitor and SyntheticTypeVisitor methods with the exception of TypeAliasType abstract.

This thankfully required fairly minimal changes. I ended up needing to make only three non-trivial changes:

1. The visitor for PlaceholderType was moved out of TypeVisitor into SyntheticTypeVisitor. My understanding is that PlaceholderType is a semantic analysis only type, so this ought to be safe.

2. As a consequence of 1, I ended up removing the existing PlaceholderType visitor method from TypeTranslator. (It seems that method was added about 6 months ago when PlaceholderType was first introduced, and was untouched since then).

3. TypeIndirectionVisitor was turned from a SyntheticTypeVisitor into a TypeVisitor. I believe we call this visitor only in the final pass, after the type-checking phase.

mypy/fixup.py

@@ -185,6 +185,10 @@ def visit_overloaded(self, t: Overloaded) -> None:
         for ct in t.items():
             ct.accept(self)
 
+    def visit_erased_type(self, o: Any) -> None:
+        # This type should exist only temporarily during type inference
+        raise RuntimeError("Shouldn't get here", o)
+
     def visit_deleted_type(self, o: Any) -> None:
         pass  # Nothing to descend into.
 

mypy/indirection.py

@@ -1,6 +1,6 @@
 from typing import Dict, Iterable, List, Optional, Set, Union
 
-from mypy.types import SyntheticTypeVisitor
+from mypy.types import TypeVisitor
 import mypy.types as types
 from mypy.util import split_module_names
 
@@ -15,7 +15,7 @@ def extract_module_names(type_name: Optional[str]) -> List[str]:
         return []
 
 
-class TypeIndirectionVisitor(SyntheticTypeVisitor[Set[str]]):
+class TypeIndirectionVisitor(TypeVisitor[Set[str]]):
     """Returns all module references within a particular type."""
 
     def __init__(self) -> None:
@@ -39,12 +39,6 @@ def _visit(self, typ_or_typs: Union[types.Type, Iterable[types.Type]]) -> Set[st
     def visit_unbound_type(self, t: types.UnboundType) -> Set[str]:
         return self._visit(t.args)
 
-    def visit_type_list(self, t: types.TypeList) -> Set[str]:
-        return self._visit(t.items)
-
-    def visit_callable_argument(self, t: types.CallableArgument) -> Set[str]:
-        return self._visit(t.typ)
-
     def visit_any(self, t: types.AnyType) -> Set[str]:
         return set()
 
@@ -90,23 +84,14 @@ def visit_tuple_type(self, t: types.TupleType) -> Set[str]:
     def visit_typeddict_type(self, t: types.TypedDictType) -> Set[str]:
         return self._visit(t.items.values()) | self._visit(t.fallback)
 
-    def visit_raw_expression_type(self, t: types.RawExpressionType) -> Set[str]:
-        assert False, "Unexpected RawExpressionType after semantic analysis phase"
-
     def visit_literal_type(self, t: types.LiteralType) -> Set[str]:
         return self._visit(t.fallback)
 
-    def visit_star_type(self, t: types.StarType) -> Set[str]:
-        return set()
-
     def visit_union_type(self, t: types.UnionType) -> Set[str]:
         return self._visit(t.items)
 
     def visit_partial_type(self, t: types.PartialType) -> Set[str]:
         return set()
 
-    def visit_ellipsis_type(self, t: types.EllipsisType) -> Set[str]:
-        return set()
-
     def visit_type_type(self, t: types.TypeType) -> Set[str]:
         return self._visit(t.item)

mypy/server/astmerge.py

@@ -56,10 +56,10 @@
 )
 from mypy.traverser import TraverserVisitor
 from mypy.types import (
-    Type, SyntheticTypeVisitor, Instance, AnyType, NoneType, CallableType, DeletedType,
+    Type, SyntheticTypeVisitor, Instance, AnyType, NoneType, CallableType, ErasedType, DeletedType,
     TupleType, TypeType, TypeVarType, TypedDictType, UnboundType, UninhabitedType, UnionType,
     Overloaded, TypeVarDef, TypeList, CallableArgument, EllipsisType, StarType, LiteralType,
-    RawExpressionType, PartialType,
+    RawExpressionType, PartialType, PlaceholderType,
 )
 from mypy.util import get_prefix, replace_object_state
 from mypy.typestate import TypeState
@@ -373,6 +373,10 @@ def visit_overloaded(self, t: Overloaded) -> None:
         if t.fallback is not None:
             t.fallback.accept(self)
 
+    def visit_erased_type(self, t: ErasedType) -> None:
+        # This type should exist only temporarily during type inference
+        raise RuntimeError
+
     def visit_deleted_type(self, typ: DeletedType) -> None:
         pass
 
@@ -429,6 +433,10 @@ def visit_union_type(self, typ: UnionType) -> None:
         for item in typ.items:
             item.accept(self)
 
+    def visit_placeholder_type(self, t: PlaceholderType) -> None:
+        for item in t.args:
+            item.accept(self)
+
     # Helpers
 
     def fixup(self, node: SN) -> SN:

mypy/server/deps.py

@@ -96,7 +96,7 @@ class 'mod.Cls'. This can also refer to an attribute inherited from a
 from mypy.types import (
     Type, Instance, AnyType, NoneType, TypeVisitor, CallableType, DeletedType, PartialType,
     TupleType, TypeType, TypeVarType, TypedDictType, UnboundType, UninhabitedType, UnionType,
-    FunctionLike, Overloaded, TypeOfAny, LiteralType, get_proper_type, ProperType
+    FunctionLike, Overloaded, TypeOfAny, LiteralType, ErasedType, get_proper_type, ProperType
 )
 from mypy.server.trigger import make_trigger, make_wildcard_trigger
 from mypy.util import correct_relative_import
@@ -901,6 +901,10 @@ def visit_overloaded(self, typ: Overloaded) -> List[str]:
             triggers.extend(self.get_type_triggers(item))
         return triggers
 
+    def visit_erased_type(self, t: ErasedType) -> List[str]:
+        # This type should exist only temporarily during type inference
+        assert False, "Should not see an erased type here"
+
     def visit_deleted_type(self, typ: DeletedType) -> List[str]:
         return []
 

mypy/type_visitor.py

@@ -34,12 +34,6 @@ class TypeVisitor(Generic[T]):
     The parameter T is the return type of the visit methods.
     """
 
-    def _notimplemented_helper(self, name: str) -> NotImplementedError:
-        return NotImplementedError("Method {}.visit_{}() not implemented\n"
-                                   .format(type(self).__name__, name)
-                                   + "This is a known bug, track development in "
-                                   + "'https://github.com/JukkaL/mypy/issues/730'")
-
     @abstractmethod
     def visit_unbound_type(self, t: UnboundType) -> T:
         pass
@@ -56,8 +50,9 @@ def visit_none_type(self, t: NoneType) -> T:
     def visit_uninhabited_type(self, t: UninhabitedType) -> T:
         pass
 
+    @abstractmethod
     def visit_erased_type(self, t: ErasedType) -> T:
-        raise self._notimplemented_helper('erased_type')
+        pass
 
     @abstractmethod
     def visit_deleted_type(self, t: DeletedType) -> T:
@@ -75,8 +70,9 @@ def visit_instance(self, t: Instance) -> T:
     def visit_callable_type(self, t: CallableType) -> T:
         pass
 
+    @abstractmethod
     def visit_overloaded(self, t: Overloaded) -> T:
-        raise self._notimplemented_helper('overloaded')
+        pass
 
     @abstractmethod
     def visit_tuple_type(self, t: TupleType) -> T:
@@ -105,9 +101,6 @@ def visit_type_type(self, t: TypeType) -> T:
     def visit_type_alias_type(self, t: TypeAliasType) -> T:
         raise NotImplementedError('TODO')
 
-    def visit_placeholder_type(self, t: PlaceholderType) -> T:
-        raise RuntimeError('Internal error: unresolved placeholder type {}'.format(t.fullname))
-
 
 @trait
 class SyntheticTypeVisitor(TypeVisitor[T]):
@@ -135,6 +128,10 @@ def visit_ellipsis_type(self, t: EllipsisType) -> T:
     def visit_raw_expression_type(self, t: RawExpressionType) -> T:
         pass
 
+    @abstractmethod
+    def visit_placeholder_type(self, t: PlaceholderType) -> T:
+        pass
+
 
 @trait
 class TypeTranslator(TypeVisitor[Type]):
@@ -235,9 +232,6 @@ def visit_overloaded(self, t: Overloaded) -> Type:
     def visit_type_type(self, t: TypeType) -> Type:
         return TypeType.make_normalized(t.item.accept(self), line=t.line, column=t.column)
 
-    def visit_placeholder_type(self, t: PlaceholderType) -> Type:
-        return PlaceholderType(t.fullname, self.translate_types(t.args), t.line)
-
 
 @trait
 class TypeQuery(SyntheticTypeVisitor[T]):

mypy/typeanal.py

@@ -13,10 +13,10 @@
 from mypy.options import Options
 from mypy.types import (
     Type, UnboundType, TypeVarType, TupleType, TypedDictType, UnionType, Instance, AnyType,
-    CallableType, NoneType, DeletedType, TypeList, TypeVarDef, SyntheticTypeVisitor,
+    CallableType, NoneType, ErasedType, DeletedType, TypeList, TypeVarDef, SyntheticTypeVisitor,
     StarType, PartialType, EllipsisType, UninhabitedType, TypeType, replace_alias_tvars,
     CallableArgument, get_type_vars, TypeQuery, union_items, TypeOfAny,
-    LiteralType, RawExpressionType, PlaceholderType, get_proper_type, ProperType
+    LiteralType, RawExpressionType, PlaceholderType, Overloaded, get_proper_type, ProperType
 )
 
 from mypy.nodes import (
@@ -456,6 +456,10 @@ def visit_none_type(self, t: NoneType) -> Type:
     def visit_uninhabited_type(self, t: UninhabitedType) -> Type:
         return t
 
+    def visit_erased_type(self, t: ErasedType) -> Type:
+        # This type should exist only temporarily during type inference
+        assert False, "Internal error: Unexpected erased type"
+
     def visit_deleted_type(self, t: DeletedType) -> Type:
         return t
 
@@ -490,6 +494,14 @@ def visit_callable_type(self, t: CallableType, nested: bool = True) -> Type:
                                   variables=self.anal_var_defs(variables))
         return ret
 
+    def visit_overloaded(self, t: Overloaded) -> Type:
+        # Overloaded types are manually constructed in semanal.py by analyzing the
+        # AST and combining together the Callable types this visitor converts.
+        #
+        # So if we're ever asked to reanalyze an Overloaded type, we know it's
+        # fine to just return it as-is.
+        return t
+
     def visit_tuple_type(self, t: TupleType) -> Type:
         # Types such as (t1, t2, ...) only allowed in assignment statements. They'll
         # generate errors elsewhere, and Tuple[t1, t2, ...] must be used instead.

mypy/types.py

@@ -1947,6 +1947,7 @@ def __init__(self, fullname: Optional[str], args: List[Type], line: int) -> None
         self.args = args
 
     def accept(self, visitor: 'TypeVisitor[T]') -> T:
+        assert isinstance(visitor, SyntheticTypeVisitor)
         return visitor.visit_placeholder_type(self)
 
     def serialize(self) -> str: