add_rewrite_endpoint() malfunction

[Fike]

1. If add_rewrite_endpoint() is called just right from plugin file, it will result in standard PHP error, telling that $wp_rewrite isn't initialized yet (call to blahblahblah on a non-object). I guess there should be placed _doing_it_wrong() function explaining that add_rewrite_point should be called during 'init' action (it would be even better if add_rewrite_endpoint() would automatically store passed arguments until 'init' action and would tell developer that his callings are late if add_rewrite_point() is called after uri parsing - as for me, finding the right action during core interaction is VERY complicated).
2. add_rewrite_endpoint() doesn't work on my localhost at all (404 is being returned without any additional query vars; i've tried adding endpoint 'json' to EP_ALL, EP_PAGES, EP_PERMALINKS, etc. and calling site/page/json and site/page/json/x), even if i just copy example code and declare new query var through 'query_vars' filter. Tried this on customized theme and on fresh install with twenty-eleven theme with no success.

[SergeyBiryukov]

Point 1 also applies to add_feed() (#4619, #20431) and the other Rewrite API functions, I suppose. There's a note in the ​Codex article:

Note that these rules are usually called inside the init hook.

I could not reproduce point 2. My steps:

1. Copy the example from Codex into a function:

   function add_json_rewrite_endpoint() {
   	add_rewrite_endpoint( 'json', EP_PERMALINK | EP_PAGES );
   }
   add_action( 'init', 'add_json_rewrite_endpoint' );
   

2. Flush rewrite rules by visiting Permalink Settings screen.
3. A post with the endpoint (e.g. /2008/02/hello-world/json/) is properly displayed, without a 404 error.

[Fike]

Looks like point 2 is resolved - that's more codex problem than core problem.
Calling $wp_rewrite->flush_rules() after adding new endpoint did the job (saving new permalinks in settings didn't). Now i'm completely lost - why add_rewrite_endpoint() should be called during each request, while it is added once and forever after flush_rules()?

[duck_]

Replying to Fike:

Calling $wp_rewrite->flush_rules() after adding new endpoint did the job (saving new permalinks in settings didn't). Now i'm completely lost - why add_rewrite_endpoint() should be called during each request, while it is added once and forever after flush_rules()?

Because if rules get flushed again at a later point (e.g. user visiting permalinks options page) then your endpoint will be lost as it wasn't registered on that page load.

Closing this ticket as invalid.