Drupal blog: function deprecation message

After submitting a form, the blog shows:

Deprecated function: Function create_function() is deprecated in GeSHi->_optimize_regexp_list_tokens_to_string() (line 4698 of vendor/geshi/geshi/src/geshi.php).

changed title from Drupal blog deprecation message to Drupal blog: function deprecation message

assigned to @lavamind

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This is due to a recent upgrade on the Drupal platform from PHP 7.0 to PHP 7.3. To get rid of this harmless warning, we'd need to upgrade that vendored library as well, and I'm unsure we really want to go down that path since we're currently in the process of migrating the blog to Lektor. What do you think?

Jérôme Charaoui commented:

This is due to a recent upgrade on the Drupal platform from PHP 7.0 to PHP 7.3. To get rid of this harmless warning, we'd need to upgrade that vendored library as well, and I'm unsure we really want to go down that path since we're currently in the process of migrating the blog to Lektor. What do you think?

On the one hand, the blog is already broken in other ways, so this isn't a big problem. On the other hand, it's a large red box at the top of the web page. Most of the other breakage is subtle and most people won't notice, but the red box is scary (even though the message is only informational), and it looks bad.

Is the concern that upgrading the vendored library will cause other breakage or is it time consuming?

I'm concerned it might create breakage and it might also be time consuming because for some reason the dependencies in that site aren't managed using composer so I'd have to either find some way of using composer without messing up the other dependencies, or download a new library blob and drop it in the git repository... All this while I'm not even sure why that library exists on the blog and what it's used for. I think it has something to do with syntax highlighting...