Compression::Util v0.18 times out from repeated signature/@_ warnings

Start by reproducing the Compression::Util v0.18 CPAN test timeout on PerlOnJava and compare its warning output with the standard Perl oracle. Investigate warning classification and emission for @_ in signatured subroutines, including repeated-warning overhead. Done means the suite completes within a reasonable time while preserving standard Perl warning behavior.

Summary

The Compression::Util v0.18 CPAN test times out on PerlOnJava because the runtime emits an extremely large number of repeated warnings while compiling/executing the module:

Use of @_ in subroutine entry with signatured subroutine is experimental

The standard Perl test suite is the behavioral source of truth and passes completely.

Reproduction

In CPAN random tester run 20260916-111623-23683, Compression::Util v0.18:

• Build.PL and Build succeed on PerlOnJava.
• The test run reaches the module test phase but produces thousands of repeated experimental::args_array_with_signatures warnings.
• The tester aborts after the 120-second soft limit because there has been no test output for 60 seconds.
• No Compression::Util assertion failure is reported.

The affected module is pure Perl. The behavior was observed with both the JVM and interpreter backends when loading the module.

Standard Perl oracle

Using the unmodified CPAN distribution and ordinary system Perl:

• 49 test files ran.
• 1,054 tests passed.
• The only skipped test was optional POD coverage requiring Test::Pod::Coverage.
• Result: PASS.

Therefore standard Perl behavior—not the warning-heavy PerlOnJava run—is the compatibility target.

Expected behavior

PerlOnJava should match standard Perl's warning semantics and complete the Compression::Util test suite within a reasonable time. In particular, repeated warnings for the same source constructs should not turn a passing pure-Perl suite into a timeout.

Additional evidence

The same Compression::Util timeout is present in the project's CPAN compatibility report dated 2026-08-29, so this appears recurrent rather than a one-off tester timeout.

Please investigate warning classification/emission for @_ use in signatured subroutines, including warning deduplication or excessive diagnostic overhead. The fix should preserve the warning behavior required by standard Perl.