Mark Cwd::getcwd results as tainted under -T

[fglock]

Summary

Under taint mode (-T), PerlOnJava returns the value of Cwd::getcwd() as a clean scalar. Standard Perl marks this operating-system-derived value as tainted.

This affects both PerlOnJava backends and causes Data::Compare 1.29's taint test to enter plugin discovery when it should disable plugins.

Minimal reproducer

use strict;
use warnings;
use Scalar::Util qw(tainted);
use Cwd qw(getcwd);

print tainted(getcwd()) ? "tainted\n" : "clean\n";

Run with taint mode enabled:

perl -T reproducer.pl
jperl -T reproducer.pl
jperl --interpreter -T reproducer.pl

Results:

• system Perl: tainted
• PerlOnJava JVM backend: clean
• PerlOnJava interpreter backend: clean

CPAN integration evidence

CPAN random-tester run 20260825-173145-22349 tested the pure-Perl Data::Compare 1.29 distribution.

• System Perl: all 17 test files and 77 assertions pass.
• PerlOnJava: the other 16 test files pass with 76 assertions; t/taint.t exits before producing its assertion.
• Running t/realtainttest directly fails on both PerlOnJava backends with Insecure dependency in chdir while running with -T switch from File::Find.

Data::Compare intentionally guards plugin discovery with logic equivalent to:

register_plugins() unless tainted(getcwd()) || !chdir($cwd);

Because PerlOnJava reports getcwd() as clean, it scans plugin directories through File::Find. That later reaches a correctly enforced taint check and aborts. Standard Perl skips plugin discovery as intended.

Expected behavior

Cwd::getcwd() should return a tainted scalar while -T is active, matching standard Perl.

Acceptance criteria

• Add a focused project regression test, validated first with standard Perl, for tainted(Cwd::getcwd()) under -T.
• Make the regression pass on both the JVM and interpreter backends.
• Make Data::Compare 1.29's unchanged t/taint.t pass.
• Preserve current behavior when taint mode is not enabled.