Initialize FuncDef.arguments in deserialize

Author: fperrin

mypy/nodes.py

@@ -641,7 +641,7 @@ def set_line(self,
 class FuncItem(FuncBase):
     """Base class for nodes usable as overloaded function items."""
 
-    __slots__ = ('arguments',  # Note that can be None if deserialized (type is a lie!)
+    __slots__ = ('arguments',  # Note that items can be None if deserialized (type is a lie!)
                  'arg_names',  # Names of arguments
                  'arg_kinds',  # Kinds of arguments
                  'min_args',  # Minimum number of arguments
@@ -657,7 +657,7 @@ class FuncItem(FuncBase):
                  'expanded',  # Variants of function with type variables with values expanded
                  )
 
-    __deletable__ = ('arguments', 'max_pos', 'min_args')
+    __deletable__ = ('max_pos', 'min_args')
 
     def __init__(self,
                  arguments: List[Argument],
@@ -770,8 +770,10 @@ def deserialize(cls, data: JsonDict) -> 'FuncDef':
         # NOTE: ret.info is set in the fixup phase.
         ret.arg_names = data['arg_names']
         ret.arg_kinds = [ArgKind(x) for x in data['arg_kinds']]
+        ret.arguments = []
+        for argname, argkind in zip(ret.arg_names, ret.arg_kinds):
+            ret.arguments += [Argument(Var(argname or ""), None, None, argkind)]
         # Leave these uninitialized so that future uses will trigger an error
-        del ret.arguments
         del ret.max_pos
         del ret.min_args
         return ret

mypy/types.py

@@ -1236,7 +1236,7 @@ def __init__(self,
             self.def_extras = {
                 'first_arg': (
                     definition.arguments[0].variable.name
-                    if (getattr(definition, 'arguments', None)
+                    if (definition.arguments
                         and definition.arg_names
                         and definition.info
                         and not definition.is_static)