Remove some "if type is None" style checks (#7120)

This pull request is a continuation of my quest to make mypy cleanly
type-check under the `--warn-unreachable` flag.

It removes some unnecessary checks we're performing against Type-related
variables. Specifically:

1. We had some old code that checked if `t.accept(TypeJoinVisitor(s))`
   would return None. I believe this check was added back in 2014: after
   auditing our type visitors, it no longer seems relevant today.

2. We had a few unnecessary `if some_instance.type is not None` style
   checks. I believe we always set the TypeInfo when constructing Instance
   classes these days, so this check also seems unnecessary.

3. Finally, we had a "if TypeInfo.bases does not actually contain Instances"
   style check around some protocol-related code. I'm not really sure
   why, but TypeInfo.bases is annotated to be of type `List[Instance]`
   so it should be fine to remove these checks as well.

Author: Michael0x2a

mypy/join.py

@@ -48,14 +48,6 @@ def join_simple(declaration: Optional[Type], s: Type, t: Type) -> Type:
         s, t = t, s
 
     value = t.accept(TypeJoinVisitor(s))
-
-    if value is None:
-        # XXX this code path probably should be avoided.
-        # It seems to happen when a line (x = y) is a type error, and
-        # it's not clear that assuming that x is arbitrary afterward
-        # is a good idea.
-        return declaration
-
     if declaration is None or is_subtype(value, declaration):
         return value
 

mypy/newsemanal/semanal_classprop.py

@@ -113,11 +113,10 @@ def check_protocol_status(info: TypeInfo, errors: Errors) -> None:
     """Check that all classes in MRO of a protocol are protocols"""
     if info.is_protocol:
         for type in info.bases:
-            if not isinstance(type, Instance) or not type.type.is_protocol:
-                if type.type.fullname() != 'builtins.object':
-                    def report(message: str, severity: str) -> None:
-                        errors.report(info.line, info.column, message, severity=severity)
-                    report('All bases of a protocol must be protocols', 'error')
+            if not type.type.is_protocol and type.type.fullname() != 'builtins.object':
+                def report(message: str, severity: str) -> None:
+                    errors.report(info.line, info.column, message, severity=severity)
+                report('All bases of a protocol must be protocols', 'error')
 
 
 def calculate_class_vars(info: TypeInfo) -> None:

mypy/semanal_pass3.py

@@ -176,9 +176,8 @@ def visit_class_def(self, tdef: ClassDef) -> None:
             self.analyze_types(types, tdef.info)
             for type in tdef.info.bases:
                 if tdef.info.is_protocol:
-                    if not isinstance(type, Instance) or not type.type.is_protocol:
-                        if type.type.fullname() != 'builtins.object':
-                            self.fail('All bases of a protocol must be protocols', tdef)
+                    if not type.type.is_protocol and type.type.fullname() != 'builtins.object':
+                        self.fail('All bases of a protocol must be protocols', tdef)
         # Recompute MRO now that we have analyzed all modules, to pick
         # up superclasses of bases imported from other modules in an
         # import loop. (Only do so if we succeeded the first time.)

mypy/suggestions.py

@@ -542,10 +542,7 @@ def __init__(self, module: Optional[str], graph: Graph) -> None:
         self.graph = graph
 
     def visit_instance(self, t: Instance) -> str:
-        if t.type is not None:
-            s = t.type.fullname() or t.type.name() or None
-        else:
-            s = None
+        s = t.type.fullname() or t.type.name() or None
         if s is None:
             return '<???>'
         if s in reverse_builtin_aliases:

mypy/types.py

@@ -1947,10 +1947,7 @@ def visit_deleted_type(self, t: DeletedType) -> str:
             return "<Deleted '{}'>".format(t.source)
 
     def visit_instance(self, t: Instance) -> str:
-        if t.type is not None:
-            s = t.type.fullname() or t.type.name() or '<???>'
-        else:
-            s = '<?>'
+        s = t.type.fullname() or t.type.name() or '<???>'
         if t.erased:
             s += '*'
         if t.args != []:
@@ -2081,10 +2078,7 @@ def list_str(self, a: List[Type]) -> str:
         """
         res = []
         for t in a:
-            if isinstance(t, Type):
-                res.append(t.accept(self))
-            else:
-                res.append(str(t))
+            res.append(t.accept(self))
         return ', '.join(res)
 
 
@@ -2101,9 +2095,7 @@ def strip_type(typ: Type) -> Type:
 
 
 def is_named_instance(t: Type, fullname: str) -> bool:
-    return (isinstance(t, Instance) and
-            t.type is not None and
-            t.type.fullname() == fullname)
+    return isinstance(t, Instance) and t.type.fullname() == fullname
 
 
 def copy_type(t: Type) -> Type: