Improvement: #13420 - Update logic of nodes._check_initialpaths_for_relpath

[sashko1988]

Updates logic of nodes._check_initialpaths_for_relpath

An even better fix for #13420 and this discussion - #13413

I still wasn't quite happy with the performance.

So after close examination of what nodes._check_initialpaths_for_relpath does, I came up with the PR changes.

Previous logic:

• Iterate over the set of initial_paths.
• try to find common path of given path and current iteration initial path
• if common path exists - compare it with current iteration initial path
• if common path is the same as the current iteration initial path, find path relative to given path and return

Instead, I propose the following:

• Check if the given path is in initial_paths.
  • if it is, then we know that relative_to will return ".", and function should return ""
• check failed, check if any parent of the given path is in initial_paths. If it is, then return the relative path of the given path and that parent.

Performance changes for collecting 1000 tests with stucture described in #13420 and #13413 (times are almost the same for main and 8.3.x branches):

Base

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     5821    2.591    0.000   83.172    0.014 nodes.py:547(_check_initialpaths_for_relpath)

With improved logic

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     5821    0.020    0.000    0.337    0.000 nodes.py:547(_check_initialpaths_for_relpath)

PS Couple of questions:

1. Should I create a separate issue for that PR or associate Slow collection time when tests are not in a relative folder to the current working folder #13420 with it?
2. Should I create a changelog entry?
3. Should I add myself to the authors?)

[RonnyPfannschmidt]

Clever

Let's associate the pr id and mention further improvement

[nicoddemus]

Nice catch! Thanks!

Changelog updated as requested.

[nicoddemus]

Should I add myself to the authors?)

Yes, you are welcome to. 👍

[sashko1988]

@nicoddemus thanks for editing the changelog entry!

[sashko1988]

@nicoddemus @RonnyPfannschmidt
Can it also be backported to 8.3.x?

[patchback]

Backport to 8.3.x: 💚 backport PR created

✅ Backport PR branch: patchback/backports/8.3.x/bd6877e5874b50ee57d0f63b342a67298ee9a1c3/pr-13448

Backported as #13451

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