Use sphinx-notfound-page by default to create a generic 404 page

We use the sphinx-notfound-page extension to create a generic page for
each project. By default we use the same Maze Found ASCII art, but the
user can customize it by defining specific configs from the sphinx-notfound-page.

Author: humitos

readthedocs/doc_builder/python_environments.py

@@ -278,6 +278,7 @@ def install_core_requirements(self):
                 ),
                 'sphinx-rtd-theme<0.5',
                 'readthedocs-sphinx-ext<0.6'
+                'sphinx-notfound-page',
             ])
 
         cmd = copy.copy(pip_install_cmd)
@@ -383,7 +384,10 @@ def install_core_requirements(self):
         if self.config.doctype == 'mkdocs':
             pip_requirements.append('mkdocs')
         else:
-            pip_requirements.append('readthedocs-sphinx-ext')
+            pip_requirements.extend([
+                'readthedocs-sphinx-ext',
+                'sphinx-notfound-page',
+            ])
             requirements.extend(['sphinx', 'sphinx_rtd_theme'])
 
         cmd = [
@@ -397,7 +401,7 @@ def install_core_requirements(self):
         cmd.extend(requirements)
         self.build_env.run(
             *cmd,
-            cwd=self.checkout_path  # noqa - no comma here in py27 :/
+            cwd=self.checkout_path,
         )
 
         pip_cmd = [

readthedocs/doc_builder/templates/doc_builder/conf.py.tmpl

@@ -133,3 +133,35 @@ if 'extensions' in globals():
     extensions.insert(0, "readthedocs_ext.readthedocs")
 else:
     extensions = ["readthedocs_ext.readthedocs"]
+
+
+# Define default 404 page body
+if 'notfound_context' not in globals():
+    notfound_context = {
+        'body': '''
+<pre style="line-height: 1.25; white-space: pre;">
+        \          SORRY            /
+         \                         /
+          \    This page does     /
+           ]   not exist yet.    [    ,'|
+           ]                     [   /  |
+           ]___               ___[ ,'   |
+           ]  ]\             /[  [ |:   |
+           ]  ] \           / [  [ |:   |
+           ]  ]  ]         [  [  [ |:   |
+           ]  ]  ]__     __[  [  [ |:   |
+           ]  ]  ] ]\ _ /[ [  [  [ |:   |
+           ]  ]  ] ] (#) [ [  [  [ :===='
+           ]  ]  ]_].nHn.[_[  [  [
+           ]  ]  ]  HHHHH. [  [  [
+           ]  ] /   `HH("N  \ [  [
+           ]__]/     HHH  "  \[__[
+           ]         NNN         [
+           ]         N/"         [
+           ]         N H         [
+          /          N            \
+         /           q,            \
+        /                           \
+</pre>
+'''
+    }