Unsaved changes prompt triggered by "content_save_pre" filter

[elliotcondon]

Hi team,

There is a bug in WordPress 5.3-beta1 causing the "Unsaved changes promp" to appear when navigating away from an updated post.

The issue is triggered by any PHP code that modifies the "post_content" value outside of the editor, causing the block editor to incorrectly believe the user has unsaved changes. I believe this is due to some logic within the calculate the wp.data.select('core/editor').isEditedPostDirty() function.

There are many filters available to modify the "post_content" value such as "content_save_pre".

Adding a simple callback to perform a str_replace() will replicate the issue. A common example of this being used in the real-world would be a company name change.

<?php
add_filter('content_save_pre', function( $content ){
        return str_replace("Company Name 1", "Company Name 2", $content);
});

Steps to reproduce:

1. Add the above code to functions.php
2. Edit a post and include the text "Company Name 1" anywhere in the content
3. Publish the post
4. Navigate away from the post
5. Notice the unload prompt

[elliotcondon]

Unload prompt

[youknowriad]

Thanks for the issue @elliotcondon This has been also reported upstream and a fix is being worked on.

​https://github.com/WordPress/gutenberg/issues/17491