Meta tags from other modules removed even if no values provided by Metatag

Disregard this comment. Wrong page by accident. Sorry.

This isn't strictly a Novice issue..

The problem is that Metatag only checks if there could be a value, not whether there actually is a value.

Per #2502453: How to best use rel=next/prev in Views pages?, this also affects Clear Pagination.

Is there any progress with this issue?

I found https://www.drupal.org/node/2415983.
We got this in comments.

* Removes tags added by core that are now handled by metatag.

So i think metatag should take care only about core tags, and the user shoud handle other tags from modules and themes by himself.

Or maybe we can add ['#access'] to render array instead unset element, and then implement theme_html_tag() to handle new key.

Disable access to tags instead of unset it.

Typo in this patch

+  $elements['system_meta_generator']['#access'] = false;;

use #10

I have the same problem, my own "prev" and "next" tags are deleted by Metatag module.
To solve this, I use drupal_add_html_head() instead of drupal_add_html_head_link()

 drupal_add_html_head([
          '#tag'        => 'link',
          '#attributes' => [
            'href' => $prev_link,
            'rel'  => 'prev',
          ],
        ], 'pager_prev_link');
      }

+1 to hver's solution above. My metatags are being deleted by the Metatag module.

I used the following module on github out of the box: https://github.com/nlisgo/nextprev_links but changed the drupal_add_html_head_link to the following drupal_add_html_head so that metatag doesn't intercept the metatags.

drupal_add_html_head(array(
'#tag' => 'link',
'#attributes' => array(
'href' => $head_link['href'],
'rel' => 'next',
),
), 'pager_next_link');

With current patch metatag module will not delete any tags anymore.
It only disable access to it.

You can now chose tags to render

/**
 * Implements hook_html_head_alter().
 */
function MYMODULE_html_head_alter(&$els) {
  $els['metatag_prev']['#access'] = false;
  $els['MYTAG_prev']['#access'] = true;
}

/**
 * Implements hook_module_implements_alter().
 *
 * Run MYMODULE_html_head_alter() after all other modules.
 */
function link_rel_module_implements_alter(&$implementations, $hook) {
  $module_name = 'MYMODULE';
  if ($hook == 'html_head_alter') {
    $group = $implementations [$module_name];
    unset($implementations [$module_name]);
    $implementations [$module_name] = $group;
  }
}

Does this work? I've rewritten it to loop over the meta tags actually being output on the page, and only remove meta tags that specifically match against tags it recognizes.

Ah, should probably verify that the variables are strings before running them through strtolower() X-)

This needs tests to confirm the types of meta tags that are removed.

Not Work, canonical and shortlink tags are not removed if value is empty

@giupenni: That might be because Drupal core adds those tags too?

Yes, I think this is possible.
How might to solve it?

I think we need a checkbox to control whether those core meta tags are removed anyway.

I agree

I just tested this as metatag module was removing rel prev/next added by flippy and it works nicely.

However now I get generator tag that was before removed by metatag module by not having a value, checkbox control for core meta tags will fix this so sounds like a good solution.

I added back - // Remove the default generator meta tag.
- unset($elements['system_meta_generator']);

this works for my problem.

I was thinking that maybe core meta tags could be removed by metatag module as was the case before this patch and maybe the patch should just be aimed at not removing meta tags added by other contributed modules.

If this was documented then seem like leaving the field blank in metatag module is a good solution.
Unsure which would be easier since I have only looked at the code around the lines added and removed , so just a suggestion.

Just rerolling the patch, I haven't added tests or the new option yet.

Lets finish this off for the next release.

Please give this a test - it now removes core's meta tags by default, and adds a new option allowing them to be left in place. And it adds a test to confirm the functionality works as intended.

@size and @giupenni: Please give that patch a try, let me know if it solves the problem for you.

Great job DamienMcKenna. Seems to work like a charm!

@giupenni: Thanks for the review.

Committed.

just installed 7.x-1.11+1-dev (2016-Jan-27) and works as advertised, thanks Damien