Refactoring: Remove the "erased" attribute of Instance (#12499)

It's not used for anything.

Author: JukkaL

mypy/checkexpr.py

@@ -3320,8 +3320,6 @@ def fast_container_type(
         vt = join.join_type_list(values)
         if not isinstance(vt, Instance):
             return None
-        # TODO: update tests instead?
-        vt.erased = True
         return self.chk.named_generic_type(container_fullname, [vt])
 
     def check_lst_expr(self, items: List[Expression], fullname: str,
@@ -3448,9 +3446,6 @@ def fast_dict_type(self, e: DictExpr) -> Optional[Type]:
             return None
         if stargs and (stargs[0] != kt or stargs[1] != vt):
             return None
-        # TODO: update tests instead?
-        kt.erased = True
-        vt.erased = True
         return self.chk.named_generic_type('builtins.dict', [kt, vt])
 
     def visit_dict_expr(self, e: DictExpr) -> Type:

mypy/checkmember.py

@@ -842,12 +842,7 @@ def analyze_enum_class_attribute_access(itype: Instance,
         return None
 
     enum_literal = LiteralType(name, fallback=itype)
-    # When we analyze enums, the corresponding Instance is always considered to be erased
-    # due to how the signature of Enum.__new__ is `(cls: Type[_T], value: object) -> _T`
-    # in typeshed. However, this is really more of an implementation detail of how Enums
-    # are typed, and we really don't want to treat every single Enum value as if it were
-    # from type variable substitution. So we reset the 'erased' field here.
-    return itype.copy_modified(erased=False, last_known_value=enum_literal)
+    return itype.copy_modified(last_known_value=enum_literal)
 
 
 def analyze_typeddict_access(name: str, typ: TypedDictType,

mypy/expandtype.py

@@ -93,19 +93,15 @@ def visit_type_var(self, t: TypeVarType) -> Type:
         repl = get_proper_type(self.variables.get(t.id, t))
         if isinstance(repl, Instance):
             inst = repl
-            # Return copy of instance with type erasure flag on.
-            return Instance(inst.type, inst.args, line=inst.line,
-                            column=inst.column, erased=True)
+            return Instance(inst.type, inst.args, line=inst.line, column=inst.column)
         else:
             return repl
 
     def visit_param_spec(self, t: ParamSpecType) -> Type:
         repl = get_proper_type(self.variables.get(t.id, t))
         if isinstance(repl, Instance):
             inst = repl
-            # Return copy of instance with type erasure flag on.
-            return Instance(inst.type, inst.args, line=inst.line,
-                            column=inst.column, erased=True)
+            return Instance(inst.type, inst.args, line=inst.line, column=inst.column)
         elif isinstance(repl, ParamSpecType):
             return repl.with_flavor(t.flavor)
         else:

mypy/types.py

@@ -1029,19 +1029,16 @@ def try_getting_instance_fallback(typ: ProperType) -> Optional[Instance]:
 
     """
 
-    __slots__ = ('type', 'args', 'erased', 'invalid', 'type_ref', 'last_known_value')
+    __slots__ = ('type', 'args', 'invalid', 'type_ref', 'last_known_value')
 
     def __init__(self, typ: mypy.nodes.TypeInfo, args: Sequence[Type],
-                 line: int = -1, column: int = -1, erased: bool = False,
+                 line: int = -1, column: int = -1, *,
                  last_known_value: Optional['LiteralType'] = None) -> None:
         super().__init__(line, column)
         self.type = typ
         self.args = tuple(args)
         self.type_ref: Optional[str] = None
 
-        # True if result of type variable substitution
-        self.erased = erased
-
         # True if recovered after incorrect number of type arguments error
         self.invalid = False
 
@@ -1137,15 +1134,14 @@ def deserialize(cls, data: Union[JsonDict, str]) -> 'Instance':
 
     def copy_modified(self, *,
                       args: Bogus[List[Type]] = _dummy,
-                      erased: Bogus[bool] = _dummy,
                       last_known_value: Bogus[Optional['LiteralType']] = _dummy) -> 'Instance':
         return Instance(
             self.type,
             args if args is not _dummy else self.args,
             self.line,
             self.column,
-            erased if erased is not _dummy else self.erased,
-            last_known_value if last_known_value is not _dummy else self.last_known_value,
+            last_known_value=last_known_value if last_known_value is not _dummy
+            else self.last_known_value,
         )
 
     def has_readable_member(self, name: str) -> bool: