bpo-32505: dataclasses: raise TypeError if a member variable is of type Field, but doesn't have a type annotation. (GH-6192)

If a dataclass has a member variable that's of type Field, but it doesn't have a type annotation, raise TypeError.

1 files changed, 21 insertions, 17 deletions

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 41b5b5d..5d4d4a6 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -573,22 +573,6 @@ def _get_field(cls, a_name, a_type):
     return f
 
 
-def _find_fields(cls):
-    # Return a list of Field objects, in order, for this class (and no
-    #  base classes).  Fields are found from the class dict's
-    #  __annotations__ (which is guaranteed to be ordered).  Default
-    #  values are from class attributes, if a field has a default.  If
-    #  the default value is a Field(), then it contains additional
-    #  info beyond (and possibly including) the actual default value.
-    #  Pseudo-fields ClassVars and InitVars are included, despite the
-    #  fact that they're not real fields.  That's dealt with later.
-
-    # If __annotations__ isn't present, then this class adds no new
-    #  annotations.
-    annotations = cls.__dict__.get('__annotations__', {})
-    return [_get_field(cls, name, type) for name, type in annotations.items()]
-
-
 def _set_new_attribute(cls, name, value):
     # Never overwrites an existing attribute.  Returns True if the
     #  attribute already exists.
@@ -663,10 +647,25 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
             if getattr(b, _PARAMS).frozen:
                 any_frozen_base = True
 
+    # Annotations that are defined in this class (not in base
+    #  classes).  If __annotations__ isn't present, then this class
+    #  adds no new annotations.  We use this to compute fields that
+    #  are added by this class.
+    # Fields are found from cls_annotations, which is guaranteed to be
+    #  ordered.  Default values are from class attributes, if a field
+    #  has a default.  If the default value is a Field(), then it
+    #  contains additional info beyond (and possibly including) the
+    #  actual default value.  Pseudo-fields ClassVars and InitVars are
+    #  included, despite the fact that they're not real fields.
+    #  That's dealt with later.
+    cls_annotations = cls.__dict__.get('__annotations__', {})
+
     # Now find fields in our class.  While doing so, validate some
     #  things, and set the default values (as class attributes)
     #  where we can.
-    for f in _find_fields(cls):
+    cls_fields = [_get_field(cls, name, type)
+                  for name, type in cls_annotations.items()]
+    for f in cls_fields:
         fields[f.name] = f
 
         # If the class attribute (which is the default value for
@@ -685,6 +684,11 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
             else:
                 setattr(cls, f.name, f.default)
 
+    # Do we have any Field members that don't also have annotations?
+    for name, value in cls.__dict__.items():
+        if isinstance(value, Field) and not name in cls_annotations:
+            raise TypeError(f'{name!r} is a field but has no type annotation')
+
     # Check rules that apply if we are derived from any dataclasses.
     if has_dataclass_bases:
         # Raise an exception if any of our bases are frozen, but we're not.