Put the JS embed back into script_files (#92)

As the inline comment suggests,
there are issues with putting the JS embed into the extrahead.
A theme that puts scripts at the end of the body
(none of the major themes do this) may not have loaded jquery
before this script is executed and the script will error.

Author: davidfischer

readthedocs_ext/_templates/readthedocs-insert.html.tmpl

@@ -29,6 +29,5 @@ READTHEDOCS_DATA = JSON.parse(document.getElementById('READTHEDOCS_DATA').innerH
 </script>
 
 <script type="text/javascript" src="{{ rtd_analytics_url }}" async="async"></script>
-<script type="text/javascript" src="{{ rtd_js_url }}" async="async"></script>
 
 <!-- end RTD <extrahead> -->

readthedocs_ext/readthedocs.py

@@ -111,6 +111,23 @@ def update_body(app, pagename, templatename, context, doctree):
         else:
             app.add_css_file(theme_css)
 
+    # Add the Read the Docs embed
+    # This *must* come after Sphinx has loaded jQuery as it relies on it.
+    # Unless this script is modified to not rely on jQuery (a good goal),
+    # it can't just be put into the extrahead
+    # in case a theme outputs scripts at the end of the body
+    js_file = '{}javascript/readthedocs-doc-embed.js'.format(STATIC_URL)
+    if all((
+        app.builder.name in ONLINE_BUILDERS,
+        hasattr(app.builder, 'script_files'),
+        js_file not in app.builder.script_files,
+    )):
+        if sphinx.version_info < (1, 8):
+            app.builder.script_files.append(js_file)
+        else:
+            kwargs = {'async': 'async'}     # Workaround reserved word in Py3.7
+            app.add_js_file(js_file, **kwargs)
+
     # This is monkey patched on the signal because we can't know what the user
     # has done with their `app.builder.templates` before now.
 
@@ -157,7 +174,6 @@ def rtd_render(self, template, render_context):
             if ctx.get('proxied_api_host'):
                 ctx['rtd_data']['proxied_api_host'] = ctx['proxied_api_host']
             ctx['rtd_css_url'] = '{}css/readthedocs-doc-embed.css'.format(STATIC_URL)
-            ctx['rtd_js_url'] = '{}javascript/readthedocs-doc-embed.js'.format(STATIC_URL)
             ctx['rtd_analytics_url'] = '{}javascript/readthedocs-analytics.js'.format(STATIC_URL)
             source = os.path.join(
                 os.path.abspath(os.path.dirname(__file__)),