PathTools: check Config values early before chdir

[haarg]

In a perl core build, the @INC paths will be relative. If you change directories before loading all of the files needed, they won't be able to be found. Config.pm loads some of its values at runtime, so if they are accessed after a chdir, it may fail.

One of the PathTools tests was relying on the fact that Config_heavy.pl would be loaded by Test::More, before it did a chdir. Newer Test::More won't do that, so the test would fail. Accessing the required Config values early will prevent this failure.

This same issue is unlikely to impact anything outside core, as it requires the perl core paths in @INC to be relative paths, which is normally not the case.

Fixes #23164

• This set of changes does not require a perldelta entry.

[jkeenan]

[snip]
One of the PathTools tests was relying on the fact that Config_heavy.pl would be loaded by Test::More, before it did a chdir. Newer Test::More won't do that, so the test would fail.

Do you know when that change in Test::More's behavior occurred? (That module's git log (core) doesn't show any commit messages with 'Config' or 'heavy'.)

Accessing the required Config values early will prevent this failure.

[haarg]

It is the commit you identified in #23164, which will be brought in with the next version of Test::More. Test-More/test-more@1653a15

[jkeenan]

Locally I built a branch from this p.r., then synched the latest Test-Simple into it. All tests passed, e.g.:

$ gitcurr
gh-23166-Perl-haarg-pathtools-config-before-chdir-20250331
[perl2] 2050 $ cd t; ./perl harness -v ../dist/PathTools/t/cwd_enoent.t; cd -

ok 1 - regular getcwd result on non-existent directory
ok 2 - regular getcwd errno on non-existent directory
ok 3 - regular abs_path result on non-existent directory
ok 4 - regular abs_path errno on non-existent directory
ok 5 - perl getcwd result on non-existent directory
ok 6 - perl getcwd errno on non-existent directory
ok 7 - perl abs_path result on non-existent directory
ok 8 - perl abs_path errno on non-existent directory
ok
All tests successful.
Files=1, Tests=8,  0 wallclock secs ( 0.00 usr  0.00 sys +  0.02 cusr  0.00 csys =  0.02 CPU)
Result: PASS

So this will fix #23164. However, I won't do that synching until after this p.r. is fully approved and merged into blead.

[jkeenan]

Could we get one other committer to take a look at this test change in PathTools? Thanks.