Render class name via custom template filter

```
In [4]: n.get_message().get_rendered_body()
Out[4]: '\n\n\nConfig validation error in <code></code>.\nExpected a list, got
type <code>int</code> (<code>422</code>).'
```

Author: humitos

readthedocs/config/notifications.py

@@ -249,7 +249,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected one of <code>[0, 1, true, false]</code>, got type <code>{{value.__class__}}</code> (<code>{{value}}</code>).
+            Expected one of <code>[0, 1, true, false]</code>, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             Make sure the type of the value is not a string.
             """
             ).strip(),
@@ -263,7 +263,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected one of ({{choices}}), got type <code>{{value.__class__}}</code> (<code>{{value}}</code>).
+            Expected one of ({{choices}}), got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             Double check the type of the value.
             A string may be required (e.g. <code>"3.10"</code> insted of <code>3.10</code>)
             """
@@ -278,7 +278,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a dictionary, got type <code>{{value.__class__}}</code> (<code>{{value}}</code>).
+            Expected a dictionary, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),
@@ -317,7 +317,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a string, got type <code>{{value.__class__}}</code> (<code>{{value}}</code>).
+            Expected a string, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),
@@ -330,7 +330,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a list, got type <code>{{value.__class__}}</code> (<code>{{value}}</code>).
+            Expected a list, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),

readthedocs/notifications/messages.py

@@ -58,12 +58,21 @@ def get_display_icon_classes(self):
 
         return " ".join(classes)
 
+    def _prepend_template_prefix(self, template):
+        """
+        Prepend Django {% load %} template tag.
+
+        This is required to render the notifications with custom filters/tags.
+        """
+        prefix = "{% load notifications_filters %}"
+        return prefix + "\n\n\n" + template
+
     def get_rendered_header(self):
-        template = Template(self.header)
+        template = Template(self._prepend_template_prefix(self.header))
         return template.render(context=Context(self.format_values))
 
     def get_rendered_body(self):
-        template = Template(self.body)
+        template = Template(self._prepend_template_prefix(self.body))
         return template.render(context=Context(self.format_values))
 
 

readthedocs/notifications/templatetags/notifications_filters.py

@@ -0,0 +1,9 @@
+from django import template
+
+register = template.Library()
+
+
+@register.filter
+def to_class_name(value):
+    """Output the name of the class for the given object."""
+    return value.__class__.__name__