The central way that a universal lock file is generated is by ignoring the markers in a list of dependencies. For example, given:

foo>=3 ; sys_platform == 'linux'
foo<3 ; sys_platform == 'darwin'

then a universal lock file needs to be generated by considering both foo>=3 and foo<3. Normally, the marker expressions would cause these dependencies to be disjoint.

However, not all markers should be ignored. The extra marker, for example, should still be evaluated since it isn't directly dependent on the platform.

This ticket is thus about adding a new marker evaluation routine that only looks at platform independent markers:

There does exist this routine:

But it also evaluates Python versions and its signature is a bit different.