Uploading a PDF breaks the File Block

[mrfoxtalbot]

Steps to reproduce

1. Add a file block with a PDF into a post
2. Publish the post.
3. Reload the post in the editor

What Happens?

1. With the plugin (10.8) active, the file block renders the PDF preview just fine:

2. As soon as the plugin is deactivated and we use the core version of the editor (5.7.4), if the post is reloaded, it causes a block error.

I noticed this error in the console:

Block validation: Expected tag name `a`, instead saw `object`.

Content generated by `save` function:

<div class="wp-block-file"><a href="http://localhost:10018/wp-content/uploads/2021/06/FITXA-DADOPCIO-NATURA-VIVA-2.pdf">FITXA-DADOPCIO-NATURA-VIVA-2</a><a href="http://localhost:10018/wp-content/uploads/2021/06/FITXA-DADOPCIO-NATURA-VIVA-2.pdf" class="wp-block-file__button" download>Download</a></div>

Content retrieved from post body:

<div class="wp-block-file"><object class="wp-block-file__embed" data="http://localhost:10018/wp-content/uploads/2021/06/FITXA-DADOPCIO-NATURA-VIVA-2.pdf" type="application/pdf" style="width:100%;height:600px" aria-label="Embed of FITXA-DADOPCIO-NATURA-VIVA-2."></object><a href="http://localhost:10018/wp-content/uploads/2021/06/FITXA-DADOPCIO-NATURA-VIVA-2.pdf">FITXA-DADOPCIO-NATURA-VIVA-2</a><a href="http://localhost:10018/wp-content/uploads/2021/06/FITXA-DADOPCIO-NATURA-VIVA-2.pdf" class="wp-block-file__button" download>Download</a></div>

[Mamaduka]

Hi, @mrfoxtalbot

I think this is expected behavior. Gutenberg 10.5 introduced PDF previews, including new markup with <object> - #30857.

So if a user uploads PDF with the latest version of Gutenberg and then switches to a version that doesn't support PDF previews, validation should fail.

[simison]

Yep +1, expected.

As soon as the plugin is deactivated and we use the core version of the editor (5.7.4), if the post is reloaded, it causes a block error.

This would cause issues with any block that has changes done in the plugin but not yet in the core WordPress.

[mrfoxtalbot]

Ah, that makes sense! Adding a PDF file with the plugin active will create a "special" subset of the file block which does not exist in the core version, and breaks without the plugin.

Thank you for the clarification! @simison y @Mamaduka
I am going to close this issue.