allow blank CharField to be nullable in the constructor, but the underlying type

is str (unless `null=True`)

Author: richardasymmetric

mypy_django_plugin/transformers/init_create.py

@@ -183,6 +183,13 @@ def extract_expected_types(ctx: FunctionContext, model: TypeInfo,
                                                                                              False):
                             field_type = helpers.make_optional(field_type)
 
+                        # if CharField(blank=True,...) and not nullable, then field can be None in __init__
+                        elif (
+                            helpers.has_any_of_bases(typ.type, (helpers.CHAR_FIELD_FULLNAME,)) and is_init and
+                            field_metadata.get('blank', False) and not field_metadata.get('null', False)
+                        ):
+                            field_type = helpers.make_optional(field_type)
+
                         expected_types[name] = field_type
 
     return expected_types

test-data/typecheck/fields.test

@@ -114,7 +114,28 @@ reveal_type(MyModel().id)  # E: Revealed type is 'uuid.UUID*'
 from django.db import models
 class MyModel(models.Model):
     text = models.CharField(max_length=30, blank=True)
-MyModel(text=None)  # E: Incompatible type for "text" of "MyModel" (got "None", expected "Union[str, int, Combinable]")
+MyModel(text=None) # Should allow None in constructor
 MyModel(text="")
+MyModel().text = None  # E: Incompatible types in assignment (expression has type "None", variable has type "Union[str, int, Combinable]")
 reveal_type(MyModel().text)  # E: Revealed type is 'builtins.str*'
 [/CASE]
+
+[CASE blank_and_null_char_field_allows_none]
+from django.db import models
+class MyModel(models.Model):
+    nulltext=models.CharField(max_length=1, blank=True, null=True)
+MyModel(nulltext="")
+MyModel(nulltext=None)
+MyModel().nulltext=None
+reveal_type(MyModel().nulltext)  # E: Revealed type is 'Union[builtins.str, None]'
+[/CASE]
+
+[CASE blank_and_not_null_charfield_does_not_allow_none]
+from django.db import models
+class MyModel(models.Model):
+    notnulltext=models.CharField(max_length=1, blank=True, null=False)
+MyModel(notnulltext=None)  # Should allow None in constructor
+MyModel(notnulltext="")
+MyModel().notnulltext = None  # E: Incompatible types in assignment (expression has type "None", variable has type "Union[str, int, Combinable]")
+reveal_type(MyModel().notnulltext)  # E: Revealed type is 'builtins.str*'
+[/CASE]