Improve error message

CHANGES.rst

@@ -4,6 +4,17 @@ Changelog
 1.3 (unreleased)
 ----------------
 
+- Allow to pass an error_callback for the GracefulResourceRenderer.
+  This allows to run some code in an error case, e.g. to add a user-visible
+  status message.
+  [thet]
+
+- Also handle resource resolver errors gracefully in the GracefulResourceRenderer.
+  [thet]
+
+- Improve error messages by including more detailed information.
+  [thet]
+
 - Do not wrap resource ``__repr__`` output in ``<>`` to render tracebacks
   properly in browser.
   [lenadax]
@@ -68,7 +79,7 @@ Changelog
   Modernize setup.[py|cfg].
   [jensens]
 
-- Added ``GracefulResourceRenderer``. 
+- Added ``GracefulResourceRenderer``.
   Fixes #1.
   [jensens]
 

webresource/_api.py

@@ -85,14 +85,36 @@ def include(self, include):
     def remove(self):
         """Remove resource or resource group from parent group."""
         if not self.parent:
-            raise ResourceError('Object is no member of a resource group')
+            raise ResourceError(
+                'Cannot remove resource or resource group {}.'
+                ' It is no member of a resource group.'.format(self)
+            )
         self.parent.members.remove(self)
         self.parent = None
 
     def copy(self):
         """Return a deep copy of this object."""
         return copy.deepcopy(self)
 
+    def __repr__(self):
+        """Return a string representation of the resource or resource group."""
+
+        reprs = []
+        if getattr(self, "name", None):
+            reprs.append('name="{}"'.format(self.name))
+        elif getattr(self, "path", None):
+            reprs.append('path="{}"'.format(self.path))
+        elif getattr(self, "url", None):
+            reprs.append('url="{}"'.format(self.url))
+
+        if getattr(self, "depends", None):
+            reprs.append('depends="{}"'.format(self.depends))
+
+        return '<{} {}>'.format(
+            self.__class__.__name__,
+            ", ".join(reprs) if reprs else "unnamed"
+        )
+
 
 class Resource(ResourceMixin):
     """A web resource."""
@@ -135,12 +157,16 @@ def __init__(
             additional attributes on resource tag.
         :raise ResourceError: No resource and no url given.
         """
-        if resource is None and url is None:
-            raise ResourceError('Either resource or url must be given')
         super(Resource, self).__init__(
             name=name, directory=directory, path=path,
             include=include, group=group
         )
+        if resource is None and url is None:
+            raise ResourceError(
+                'Either resource or url must be given for resource {}'.format(
+                    self
+                )
+            )
         self.depends = (
             (depends if isinstance(depends, (list, tuple)) else [depends])
             if depends else None
@@ -169,7 +195,9 @@ def file_path(self):
         """Absolute resource file path depending on operation mode."""
         directory = self.directory
         if not directory:
-            raise ResourceError('No directory set on resource.')
+            raise ResourceError(
+                'No directory set on resource {}'.format(self)
+            )
         return os.path.join(directory, self.file_name)
 
     @property
@@ -235,15 +263,6 @@ def _render_tag(self, tag, closing_tag, **attrs):
             return u'<{tag}{attrs} />'.format(tag=tag, attrs=attrs_)
         return u'<{tag}{attrs}></{tag}>'.format(tag=tag, attrs=attrs_)
 
-    def __repr__(self):
-        return (
-            '{} name="{}", depends="{}"'
-        ).format(
-            self.__class__.__name__,
-            self.name,
-            self.depends
-        )
-
 
 class ScriptResource(Resource):
     """A Javascript resource."""
@@ -323,8 +342,10 @@ def integrity(self):
     def integrity(self, integrity):
         if integrity is True:
             if self.url is not None:
-                msg = 'Cannot calculate integrity hash from external resource'
-                raise ResourceError(msg)
+                raise ResourceError(
+                    'Cannot calculate integrity hash from external resource '
+                    '{}'.format(self)
+                )
             self._integrity_hash = None
         else:
             self._integrity_hash = integrity
@@ -564,8 +585,8 @@ def add(self, member):
         """
         if not isinstance(member, (ResourceGroup, Resource)):
             raise ResourceError(
-                'Resource group can only contain instances '
-                'of ``ResourceGroup`` or ``Resource``'
+                'Resource group {} can only contain instances '
+                'of ``ResourceGroup`` or ``Resource``'.format(self)
             )
         member.parent = self
         self._members.append(member)
@@ -584,12 +605,6 @@ def _filtered_resources(self, type_, members=None):
                 resources.append(member)
         return resources
 
-    def __repr__(self):
-        return '{} name="{}"'.format(
-            self.__class__.__name__,
-            self.name
-        )
-
 
 class ResourceConflictError(ResourceError):
     """Multiple resources declared with the same name."""
@@ -634,7 +649,7 @@ def __init__(self, members):
         for member in members:
             if not isinstance(member, (Resource, ResourceGroup)):
                 raise ResourceError(
-                    'members can only contain instances '
+                    'ResourceResolver members can only contain instances '
                     'of ``ResourceGroup`` or ``Resource``'
                 )
         self.members = members
@@ -723,13 +738,38 @@ def render(self):
 class GracefulResourceRenderer(ResourceRenderer):
     """Resource renderer, which does not fail but logs an exception."""
 
-    def render(self):
+    def render(self, error_callback=None):
         lines = []
-        for resource in self.resolver.resolve():
+        resources = []
+
+        try:
+            resources = self.resolver.resolve()
+        except (
+            ResourceConflictError,
+            ResourceCircularDependencyError,
+            ResourceMissingDependencyError,
+        ) as e:
+            error_message = str(e)
+            logger.exception(error_message)
+            if error_callback:
+                error_callback(error_message)
+
+        for resource in resources:
+            error_message = None
             try:
                 lines.append(resource.render(self.base_url))
-            except (ResourceError, FileNotFoundError):
-                msg = u'Failure to render resource "{}"'.format(resource.name)
-                lines.append(u'<!-- {} - details in logs -->'.format(msg))
-                logger.exception(msg)
+            except FileNotFoundError:
+                error_message = u'File not found for resource {}'.format(
+                    resource
+                )
+            except ResourceError as e:
+                error_message = str(e)
+            finally:
+                if error_message:
+                    lines.append(u'<!-- {} - details in logs -->'.format(
+                        error_message
+                    ))
+                    logger.exception(error_message)
+                    if error_callback:
+                        error_callback(error_message)
         return u'\n'.join(lines)