#3299 - Add URI redirect for missing translations

modules/web/templates/site.conf.erb

 root /var/www/<%= @vhost %>;
 index index;
 default_type text/html;
 charset utf-8;
 
 set $index_page "index";
 
 <% if @custom_config %>
   <%= @custom_config %>
 <% end %>
@@ skipping 34 matching lines @@
     rewrite ^(.*) /${preferredLang}_$preferredRegion$1 last;
   }
   if (-e "$document_root/$preferredLang$uri")
   {
     rewrite ^(.*) /$preferredLang$1 last;
   }
   if (-e "$document_root/en$uri")
   {
     rewrite ^(.*) /en$1 last;
   }
-
 }
 
 # Redirect language URIs if no translations are found for the requested page
 
-location ~ ^/([a-z][a-z]\_[A-Z][A-Z])(/.+) {

[mathias, 2017/09/08 19:20:20]

There's a newline missing in front of the bracket.

[f.nicolaisen, 2017/09/11 07:33:14]

Acknowledged.

+location ~ ^/([a-z][a-z]\_[A-Z][A-Z])(/.+)
+{
   if (!-e "$document_root$uri")
   {
     # if there is no language+region translation, try parent language URI
     # example /es_MX/page -> /es/page
     rewrite ^/([a-z][a-z])\_([A-Z][A-Z])(/.+) /$1$3 redirect;

[mathias, 2017/09/08 19:20:20]

This seems a bit quirky, it would move the user from `/aa-AA/` to `/aa/` and
thus remove "session" information. But then it seems like that quirky stuff is
actually how it's meant to be? The Hungarian ABP pages even link directly to the
`/en/` ones where a translation is missing.. https://adblockplus.org/hu/chrome

[f.nicolaisen, 2017/09/11 07:33:14]

Yes, this is quirky - if someone has manually chosen Mexican (es-MX), and they
surf to a page that does not have a Mexican, but a Spanish (es) version
available, they will be flipped to Spanish and not return when later surfing to
a page available in Mexican. 

The existing behavior was to just show 404s in these cases, which would be
terrible experience with all those half-complete translation sets we have
currently.

We could check for an available translation on every request, and flip them back
to Mexican when possible, but that will be counter-intuitive to those who have
manually chosen a different language in the top-right selector on the page. 

The optimal solution would be to keep their last chosen language stored in
session and say "You're currently surfing the Mexican site but this page only
has Spanish translation available", but that would mean revisiting privacy
policy and server mechanics, which is out of scope for this commit.

Regarding the related CMS-generated links, I have no idea, but I *hope* they
have the same logic - I only found some hints of documented behavior in
https://github.com/adblockplus/cms/blob/master/README.md#configuration-settin...

   }
 }
 

[mathias, 2017/09/08 19:20:20]

There's a newline missing in front of the bracket.

[f.nicolaisen, 2017/09/11 07:33:14]

Acknowledged.

-location ~ ^/([a-z][a-z])(/.+) {
+location ~ ^/([a-z][a-z])(/.+)
+{
   if (!-e "$document_root$uri")
   {
     # if there is no language translation, try canonical page for default language
     # example /es/page -> /page
     rewrite ^/([a-z][a-z])(/.+) $2 redirect;
   }
 }
 
 <% if @multiplexer_locations %>
   <% @multiplexer_locations.each do |location| %>
   location <%= location %>
   {
     fastcgi_pass unix:/tmp/multiplexer-fastcgi.sock;
     include /etc/nginx/fastcgi_params;
   }
   <% end %>
 <% end %>