Template Part Not Found for badly formed wp:template-part HTML comment

[bobbingwide]

While developing the archive.html template file I encountered a problem where the Template Part Not Found message was displayed but there was no template name. The only attribute value passed to gutenberg_render_block_core_template_part() was tagName, with a value of div.

Analysis of the HTML comment that formed the wp:template-part block indicated that I was missing a comma between attributes.

<!-- wp:template-part {"slug":"footer-menu","theme":"fizzie" "className":"footer-menu"} /-->

It would be helpful if the error could be detected and a message produced.

[bobbingwide]

Another form that doesn't work, and doesn't even produce a message, is when there's no space between the block name ( template-part ) and the left curly brace, or when the wrong character has been used. eg (.

<!-- wp:template-part{"slug":"footer-menu","theme":"fizzie" "className":"footer-menu"} /-->
<!-- wp:template-part ("slug":"footer-menu", "theme":"fizzie" "className":"footer-menu"} /-->

[bobbingwide]

There are many more ways to write an invalid block tag inside an HTML comment.
I've found a few more recently while developing SB.

Too many closing curly braces.

<!-- wp:template-part {"slug":"page-footer","theme":"sb","layout":{"inherit":true}},"tagName":"footer"} /-->

I had this problem with a template-part. The extra curly brace prevented any of the attributes being set.
This caused a Warning messag from template-part.php

Warning: Undefined array key "slug" in C:\apache\htdocs\wordpress\wp-content\themes\sb\includes\template-part.php on line 78

An end block slash where it shouldn't be

<!-- wp:query-loop {"className": "sb hero" } /-->

This one took me longer to find. See bobbingwide/sb#13

[bobbingwide]

I'm closing this as wontfix. Some of the badly formed template-part tags will be removed from the templates that used them. This should improve performance very slighty and may also help anyone reading the code.