In current CP install that file reads as it should, in versions prior to 5.3 this function still exists and the file is with code, not deprecated, on my instals I can see the code in the files as expected.
The only that I can explain this to myself is that master Git is not the same as stable tag 1.2.0
Which is IMO weird because master in Git reflects the last stable code, or am I wrong?
And if I am wrong, where can we link to so we get the actual up to date code in Git?
The code in ClassicPress/ClassicPress gets built using (release-builder) into the code you see in ClassicPress/ClassicPress-release which is then ultimately what is pushed to api endpoints to be upgraded to.
To make that clear again, the parser does not run against any remote code.
It runs locally and the parser does get the right code, if you consult the DOC you can see it is correct.
What is not correct, is the link that points to git. I chose master because I thought master is … well, master. I stand corrected, and will point the thing towards the whatever last stable tag. This adds complexity because the link now needs to take a dynamic version number but it is of course doable.
We probably should document the fact that in CP, we have both a global $wp_version (returning the forked WP Version number I believe it was 4.9.15 or so) and a global $cp_version, which returns the installed CP version.
And probably this is a good moment to think about providing a function for this that does not call remote like wp_version_check does and which would return non-useful data on a CP install.
I think this is important as has been mentioned prior by others:
We need to first document what we plan to change, then change it. Discovering later that we changed something for a non-core dev is just as annoying as discovering the WP User Object is a mess