Previewing the page designated as "latest posts" shows the frontpage

[zieladam]

This continues the discussion from ​https://github.com/WordPress/gutenberg/issues/2409

The issue

• Create two pages (let's call them "My home" and "My posts")
• Go to customizer and set Homepage to be "My home" and Posts page to "My posts"
• Edit "My posts" in editor mode
• Press preview
• Confirm you got "My home" instead of "My posts"

The root cause

When you click "Open preview in new tab" while editing "My posts", Gutenberg redirects to a preview URL like this one:

​https://mywpsite.com/?page_id=5&preview_id=5&preview_nonce=12bd60d6f4&preview=true

When you visit that URL, WordPress will load the front page instead of the posts page. This is because class-wp-query.php assumes that posts page is also the front page:

​https://github.com/WordPress/WordPress/blob/b4373fafe9b87f75bf9d65e808be8049510dff8b/wp-includes/class-wp-query.php#L1032

Then, when rendering a preview, it substitutes the page_id that was requested with the value of get_option( 'page_on_front' ):

​https://github.com/WordPress/WordPress/blob/b4373fafe9b87f75bf9d65e808be8049510dff8b/wp-includes/class-wp-query.php#L1904

If I remove the preview parameters and leave only ?page_id=5, it displays the correct page.

[joyously]

As stated in the GitHub issue, that issue was only a continuation of #34005

[zieladam]

In my understanding, #34005 is about re-enabling the Visual Editor and Page Template dropdown when editing the page for Posts. The discussion in the Gutenberg issue ​https://github.com/WordPress/gutenberg/issues/2409 pivoted towards the results of previewing the page marked as "Posts page" - which indeed is unexpected due to a bug. I believe this constitutes it's own issue.

[poena]

#59438 was marked as a duplicate.

[poena]

I am testing with Twenty Twenty-Four on WordPress version 6.4.2 and it is working for me, I believe it has been fixed:
When I am in the post editor, editing the page that I have assigned as the blog page, and I click on "View page", it shows me the correct template and content.

[bvoynick]

This is still a problem in 6.4.3.

As noted in the description, reproduction requires choosing both a home page and a separate posts/blog page. If only a posts/blog page is set, this preview bug does not occur.

[poena]

I figured out what I did wrong in my testing, and I can confirm that this is still an issue in 6.5x:

In the block editor, I had clicked on "View Page", and this only uses the page slug, not the
page id, preview id, or nonce.

Clicking on the button that says "View" instead of "View Page", and then selecting
"Preview in new tab" in the drop down, does show the page selected as the homepage instead of the blog page.