Non-URL GUIDs are stripped on post update
|Reported by:||alexkingorg||Owned by:|
The post guid is run through several filters before the post is saved. the esc_url_raw() call will end up setting a GUID to an empty string if the GUID does not begin with a known/accepted protocol.
If a plugin/etc. wants to use the GUID column to store an external ID for an item brought in from another system (say a Flickr photo ID), then updating a post that has the Flickr ID as its GUID through the WP admin will end up setting the GUID for that post to .
This would need to be changed if the move was made to UUIDs for GUID values as well. Related: #6492.
A very basic patch for this specific issue is attached, but a larger discussion around how this should work is likely needed. Related: #18315