Don't allow form parameters with non-form consumes

Closes #270.

src/drf_yasg/inspectors/view.py

@@ -8,8 +8,8 @@ from rest_framework.status import is_success
 from .. import openapi
 from ..errors import SwaggerGenerationError
 from ..utils import (
-    force_real_str, force_serializer_instance, get_consumes, get_produces, guess_response_status, is_list_view,
-    merge_params, no_body, param_list_to_odict
+    filter_none, force_real_str, force_serializer_instance, get_consumes, get_produces, guess_response_status,
+    is_list_view, merge_params, no_body, param_list_to_odict
 )
 from .base import ViewInspector
 
@@ -29,7 +29,7 @@ class SwaggerAutoSchema(ViewInspector):
         body = self.get_request_body_parameters(consumes)
         query = self.get_query_parameters()
         parameters = body + query
-        parameters = [param for param in parameters if param is not None]
+        parameters = filter_none(parameters)
         parameters = self.add_manual_parameters(parameters)
 
         operation_id = self.get_operation_id(operation_keys)
@@ -167,12 +167,13 @@ class SwaggerAutoSchema(ViewInspector):
         if any(param.in_ == openapi.IN_BODY for param in manual_parameters):  # pragma: no cover
             raise SwaggerGenerationError("specify the body parameter as a Schema or Serializer in request_body")
         if any(param.in_ == openapi.IN_FORM for param in manual_parameters):  # pragma: no cover
-            if any(param.in_ == openapi.IN_BODY for param in parameters):
+            has_body_parameter = any(param.in_ == openapi.IN_BODY for param in parameters)
+            if has_body_parameter or not any(is_form_media_type(encoding) for encoding in self.get_consumes()):
                 raise SwaggerGenerationError("cannot add form parameters when the request has a request body; "
                                              "did you forget to set an appropriate parser class on the view?")
             if self.method not in self.body_methods:
-                raise SwaggerGenerationError("form parameters can only be applied to (" + ','.join(self.body_methods) +
-                                             ") HTTP methods")
+                raise SwaggerGenerationError("form parameters can only be applied to "
+                                             "(" + ','.join(self.body_methods) + ") HTTP methods")
 
         return merge_params(parameters, manual_parameters)
 

src/drf_yasg/utils.py

@@ -335,11 +335,11 @@ def get_consumes(parser_classes):
     :rtype: list[str]
     """
     media_types = [parser.media_type for parser in parser_classes or []]
-    if all(is_form_media_type(encoding) for encoding in media_types):
+    non_form_media_types = [encoding for encoding in media_types if not is_form_media_type(encoding)]
+    if len(non_form_media_types) == 0:
         return media_types
     else:
-        media_types = [encoding for encoding in media_types if not is_form_media_type(encoding)]
-        return media_types
+        return non_form_media_types
 
 
 def get_produces(renderer_classes):

tests/test_form_parameters.py

@@ -0,0 +1,46 @@
+import pytest
+from django.conf.urls import url
+from django.utils.decorators import method_decorator
+from rest_framework.authtoken.views import ObtainAuthToken
+from rest_framework.settings import api_settings
+
+from drf_yasg import openapi
+from drf_yasg.errors import SwaggerGenerationError
+from drf_yasg.generators import OpenAPISchemaGenerator
+from drf_yasg.utils import swagger_auto_schema
+
+
+def test_choice_field():
+    @method_decorator(name='post', decorator=swagger_auto_schema(
+        operation_description="Logins a user and returns a token",
+        manual_parameters=[
+            openapi.Parameter(
+                "username",
+                openapi.IN_FORM,
+                required=True,
+                type=openapi.TYPE_STRING,
+                description="Valid username or email for authentication"
+            ),
+            openapi.Parameter(
+                "password",
+                openapi.IN_FORM,
+                required=True,
+                type=openapi.TYPE_STRING,
+                description="Valid password for authentication",
+            ),
+        ]
+    ))
+    class CustomObtainAuthToken(ObtainAuthToken):
+        throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
+
+    urlpatterns = [
+        url(r'token/$', CustomObtainAuthToken.as_view()),
+    ]
+
+    generator = OpenAPISchemaGenerator(
+        info=openapi.Info(title="Test generator", default_version="v1"),
+        patterns=urlpatterns
+    )
+
+    with pytest.raises(SwaggerGenerationError):
+        generator.get_schema(None, True)