SEO rewrites don't work on front page when blogapi and url_alter modules are enabled

I ran into a problem with SEO rewrites not working on the front page when the blogapi and url_alter modules are enabled. My setup may represent an edge case, but the fix seemed pretty easy, so I wanted to point it out.

I came across this bug when I created a view block that showed posts from across different subdomains. I enabled SEO rewriting in the domain access settings so that the links would go to the correct source domain. I enabled the block for all pages, and everything appeared to work perfectly. However, when I checked the block from the front page, I found that none of the urls for content on other domains were being rewritten properly. I ended up tracing this back to an issue with the module load order and the fact that domain_access does not include() its url_outbound_alter hook until domain_init is called. Here's what I was able to figure out:

With the blogapi module enabled, at the start of a page view, blogapi_init runs and calls url() only if viewing the front page. url() in turn calls custom_url_rewrite_outbound, which on my site is being defined by the url_alter module. url_alter then calls module_implements('url_outbound_alter') to find out what modules are implementing its hook. However, at this point, based on the default module load order, domain_init has not yet been called (it will be called after blogapi_init because of alphabetical ordering). Therefore, settings_custom_url.inc has not been included and domain_url_outbound_alter has not been defined. In this case, module_implements('url_outbound_alter') does not return domain_url_outbound_alter() as a hook, but it caches the value in a static array, so even after settings_custom_url.inc is included by domain_init, future calls to module_implements('url_outbound_alter') will still not include domain_url_outbound_alter. Then, when my view is built, the domain_url_outbound_alter does not get used, and my urls are wrong. Note that on any page besides the front page, blogapi_init does not call url, so the first call to custom_url_rewrite_outbound and module_implements('url_outbound_alter') occur after domain_init has run.

My simple fix was to change the weight of the domain module in the system table to -10, so that domain_init would be called before blogapi_init. Because I have prefixed the url_alias table, I also had to change the weight of the domain_prefix module so that domain_prefix.path.inc would be included to define domain_prefix_domainpath. To be safe, I set the weight of all of the domain_* modules to -10. This has solved my problem, and now seo rewrites happen on all pages.