- Better error messages when a view callable returns a value that cannot be

  converted to a response (for example, when a view callable returns a
  dictionary without a renderer defined, or doesn't return any value at all).
  The error message now contains information about the view callable itself
  as well as the result of calling it.

4 files changed, 159 insertions, 5 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index fcd54217f..411681d81 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -11,6 +11,12 @@ Features
   http://readthedocs.org/docs/venusian/en/latest/#ignore-scan-argument for
   more information about how to use the ``ignore`` argument to ``scan``.
 
+- Better error messages when a view callable returns a value that cannot be
+  converted to a response (for example, when a view callable returns a
+  dictionary without a renderer defined, or doesn't return any value at all).
+  The error message now contains information about the view callable itself
+  as well as the result of calling it.
+
 Dependencies
 ------------
 
diff --git a/pyramid/config/util.py b/pyramid/config/util.py
index 6b7aa2fa1..4c7ecd359 100644
--- a/pyramid/config/util.py
+++ b/pyramid/config/util.py
@@ -6,7 +6,6 @@ from zope.interface import implementer
 from pyramid.interfaces import IActionInfo
 
 from pyramid.compat import (
-    string_types,
     bytes_,
     is_nonstr_iter,
     )
diff --git a/pyramid/config/views.py b/pyramid/config/views.py
index 86b139e3e..1988b532b 100644
--- a/pyramid/config/views.py
+++ b/pyramid/config/views.py
@@ -55,6 +55,7 @@ from pyramid.security import NO_PERMISSION_REQUIRED
 from pyramid.static import static_view
 from pyramid.threadlocal import get_current_registry
 from pyramid.view import render_view_to_response
+from pyramid.util import object_description
 
 from pyramid.config.util import (
     DEFAULT_PHASH,
@@ -67,6 +68,12 @@ from pyramid.config.util import (
 urljoin = urlparse.urljoin
 url_parse = urlparse.urlparse
 
+def view_description(view):
+    try:
+        return view.__text__
+    except AttributeError:
+        return object_description(view)
+
 def wraps_view(wrapper):
     def inner(self, view):
         wrapper_view = wrapper(self, view)
@@ -99,7 +106,7 @@ def preserve_view_attrs(view, wrapper):
     # "wrapped view"
     for attr in ('__permitted__', '__call_permissive__', '__permission__',
                  '__predicated__', '__predicates__', '__accept__',
-                 '__order__'):
+                 '__order__', '__text__'):
         try:
             setattr(wrapper, attr, getattr(view, attr))
         except AttributeError:
@@ -343,9 +350,19 @@ class ViewDeriver(object):
             result = view(context, request)
             response = registry.queryAdapterOrSelf(result, IResponse)
             if response is None:
-                raise ValueError(
-                    'Could not convert %r return value "%s" into a '
-                    'response object' % (view,result,))
+                if result is None:
+                    append = (' You may have forgotten to return a value from '
+                              'the view callable.')
+                elif isinstance(result, dict):
+                    append = (' You may have forgotten to define a renderer in '
+                              'the view configuration.')
+                else:
+                    append = ''
+                msg = ('Could not convert return value of the view callable %s '
+                      'into a response object. '
+                      'The value returned was %r.' + append)
+                    
+                raise ValueError(msg % (view_description(view), result))
             return response
 
         return viewresult_to_response
@@ -376,6 +393,8 @@ class DefaultViewMapper(object):
             mapped_view = self.map_class_requestonly(view)
         else:
             mapped_view = self.map_class_native(view)
+        mapped_view.__text__ = 'method %s of %s' % (
+            self.attr or '__call__', object_description(view))
         return mapped_view
 
     def map_nonclass(self, view):
@@ -388,6 +407,11 @@ class DefaultViewMapper(object):
             mapped_view = self.map_nonclass_requestonly(view)
         elif self.attr:
             mapped_view = self.map_nonclass_attr(view)
+        if self.attr is not None:
+            mapped_view.__text__ = 'attr %s of %s' % (
+                self.attr, object_description(view))
+        else:
+            mapped_view.__text__ = object_description(view)
         return mapped_view
 
     def map_class_requestonly(self, view):
diff --git a/pyramid/tests/test_config/test_views.py b/pyramid/tests/test_config/test_views.py
index 4af29325a..eb18d5c84 100644
--- a/pyramid/tests/test_config/test_views.py
+++ b/pyramid/tests/test_config/test_views.py
@@ -2282,6 +2282,113 @@ class TestViewDeriver(unittest.TestCase):
         self.config.registry.registerUtility(policy, IAuthenticationPolicy)
         self.config.registry.registerUtility(policy, IAuthorizationPolicy)
 
+    def test_function_returns_non_adaptable(self):
+        def view(request):
+            return None
+        deriver = self._makeOne()
+        result = deriver(view)
+        self.assertFalse(result is view)
+        try:
+            result(None, None)
+        except ValueError as e:
+            self.assertEqual(
+                e.args[0], 
+                'Could not convert return value of the view callable function '
+                'pyramid.tests.test_config.test_views.view into a response '
+                'object. The value returned was None. You may have forgotten '
+                'to return a value from the view callable.'
+                )
+        else: # pragma: no cover
+            raise AssertionError
+
+    def test_function_returns_non_adaptable_dict(self):
+        def view(request):
+            return {'a':1}
+        deriver = self._makeOne()
+        result = deriver(view)
+        self.assertFalse(result is view)
+        try:
+            result(None, None)
+        except ValueError as e:
+            self.assertEqual(
+                e.args[0], 
+                "Could not convert return value of the view callable function "
+                "pyramid.tests.test_config.test_views.view into a response "
+                "object. The value returned was {'a': 1}. You may have "
+                "forgotten to define a renderer in the view configuration."
+                )
+        else: # pragma: no cover
+            raise AssertionError
+        
+    def test_instance_returns_non_adaptable(self):
+        class AView(object):
+            def __call__(self, request):
+                return None
+        view = AView()
+        deriver = self._makeOne()
+        result = deriver(view)
+        self.assertFalse(result is view)
+        try:
+            result(None, None)
+        except ValueError as e:
+            msg = e.args[0]
+            self.assertTrue(msg.startswith(
+                'Could not convert return value of the view callable object '
+                '<pyramid.tests.test_config.test_views.AView object at'))
+            self.assertTrue(msg.endswith(
+                '> into a response object. The value returned was None. You '
+                'may have forgotten to return a value from the view callable.'))
+        else: # pragma: no cover
+            raise AssertionError
+
+    def test_requestonly_default_method_returns_non_adaptable(self):
+        request = DummyRequest()
+        class AView(object):
+            def __init__(self, request):
+                pass
+            def __call__(self):
+                return None
+        deriver = self._makeOne()
+        result = deriver(AView)
+        self.assertFalse(result is AView)
+        try:
+            result(None, request)
+        except ValueError as e:
+            self.assertEqual(
+                e.args[0], 
+                'Could not convert return value of the view callable '
+                'method __call__ of '
+                'class pyramid.tests.test_config.test_views.AView into a '
+                'response object. The value returned was None. You may have '
+                'forgotten to return a value from the view callable.'
+                )
+        else: # pragma: no cover
+            raise AssertionError
+
+    def test_requestonly_nondefault_method_returns_non_adaptable(self):
+        request = DummyRequest()
+        class AView(object):
+            def __init__(self, request):
+                pass
+            def theviewmethod(self):
+                return None
+        deriver = self._makeOne(attr='theviewmethod')
+        result = deriver(AView)
+        self.assertFalse(result is AView)
+        try:
+            result(None, request)
+        except ValueError as e:
+            self.assertEqual(
+                e.args[0], 
+                'Could not convert return value of the view callable '
+                'method theviewmethod of '
+                'class pyramid.tests.test_config.test_views.AView into a '
+                'response object. The value returned was None. You may have '
+                'forgotten to return a value from the view callable.'
+                )
+        else: # pragma: no cover
+            raise AssertionError
+        
     def test_requestonly_function(self):
         response = DummyResponse()
         def view(request):
@@ -3689,6 +3796,24 @@ class TestStaticURLInfo(unittest.TestCase):
                  view_attr='attr')
         self.assertEqual(config.view_kw['attr'], 'attr')
 
+class Test_view_description(unittest.TestCase):
+    def _callFUT(self, view):
+        from pyramid.config.views import view_description
+        return view_description(view)
+    
+    def test_with_text(self):
+        def view(): pass
+        view.__text__ = 'some text'
+        result = self._callFUT(view)
+        self.assertEqual(result, 'some text')
+        
+    def test_without_text(self):
+        def view(): pass
+        result = self._callFUT(view)
+        self.assertEqual(result, 
+                         'function pyramid.tests.test_config.test_views.view')
+        
+
 class DummyRegistry:
     pass