apachesolr_search_custom_page_search_form_submit() kills all $_GET parameters

Issue #502976: Other GET parameters ignored by Apache Solr Facet Blocks explains the problem. The issue has already been fixed in earlier versions.

Apache Solr Multilingual for example adds detach-auto-language-filter=1, the same way apachesolr adds retain-filters=1 when required.

Stuff like paging still works with my patch applied.

I think it has to be the other way round. apachesolr only has to grap and remove it's own stuff, but leave everything else added by users untouched during the form redirect.

If users want to add custom stuff that has to be handled by retain-filters, they have to add this using alter hooks.

It will take up useless space in the memory. Luckily the url can only go 4096 characters and we don't support POST arguments.

This problem is not specific for apachesolr. It's a common problem.
And the get parameters might already exist. The current implementation only deletes them and redirects.

Are there any other arguments against my patch?

OK, I'll accept this solution. Who will work on this patch?

Like discussed in our recent chat:

I inroduced a new variable 'apachesolr_search_protected_query_parameters' holding a list of all get parameters that should not be deleted if retain-filters is not set (see patch attached).

In apachesolr_multilingual.install I register our variable to be protected:

/**
 * Implements hook_enable().
 */
function apachesolr_multilingual_enable() {
  variable_set('apachesolr_search_protected_query_parameters',
    array_merge(
      variable_get('apachesolr_search_protected_query_parameters', array()),
      array('detach-auto-language-filter')
    )
  );
}

/**
 * Implements hook_disable().
 */
function apachesolr_multilingual_disable() {
  variable_set('apachesolr_search_protected_query_parameters',
    array_diff(
      variable_get('apachesolr_search_protected_query_parameters', array()),
      array('detach-auto-language-filter')
    )
  );
}

I would like to see the last patch to be committed. That's the solution I prefered when starting the issue and it reduces code in apachesolr_multilingual.

// We may also have filters added by facet API module. The 'f'
// is determined by variable FacetapiUrlProcessor::$filterKey. Hard
// coded here to avoid extra class loading.
if (!empty($_GET['f']) && is_array($_GET['f'])) {
...

Having this comment in the code is OK for now. From my point view, dealing with FacetapiUrlProcessor::$filterKey is a different issue.