Exposed form does not save state when it is placed in a block

Related: Exposed form in a block rendered on another page than the view is displayed breaks the "Remember the last selection" option.

Isn't that indeed a duplicate of #2551431: Exposed form in a block rendered on another page than the view is displayed breaks the "Remember the last selection" option.

I have the same problem. it seems that block form has been cached, and i co not know how to disable cache for a specific block.
https://www.drupal.org/node/2603244

At last I solve this issue by using jquery:

$.getUrlParam = function(name){
  var reg = new RegExp("(^|&)"+ name +"=([^&]*)(&|$)");
  var r = window.location.search.substr(1).match(reg);
  if (r!=null) return decodeURI(r[2]); return null;
}
	var title = $.getUrlParam('title');
	if(title){
	  $('#views-exposed-form-addressbooks-page-2 .form-text').val(title);
	}

Bug reproduced + fixed locally.

Currently extending test coverage.

Let's see what testbot has to say about it so far.

Still working on new tests.

Found and fixed a null reference exception in previous patch.

Moved cache context generation to ExposedFormPluginBase::getCacheContexts() which seems more sensible.

Still new to this cacheContexts thing. The block should expose them, not it's render array.

Added tests.

While working on this I found out that the filters could provide more specific cache contexts. See #2605038: Views Exposed Filters should provide more specific cache contexts. for more info.

Just a small nitpick ...

+++ b/core/modules/views/src/Plugin/Block/ViewsExposedFilterBlock.php
@@ -19,10 +20,19 @@
 
   /**
+   * @inheritedDoc
+   */
+  public function getCacheContexts() {

nitpick: it should be {@inheritdoc}

@dawehner

I update your comment

Thank you!

Committed/pushed to 8.1.x and cherry-picked to 8.0.x. Thanks!