Module::Build omits declared nested Perl module from blib

Start with PerlOnJava's Module::Build file-discovery and staging logic, comparing lib/AudioFile/Info/MP3/Tag.pm with the generated blib/lib tree after Build. Add focused regression coverage that checks the nested module is staged, then run t/1_read.t, t/2_write.t, and t/4_pod_coverage.t. Done means the module is available from blib/lib and the distribution tests pass like system Perl.

Summary

AudioFile::Info::MP3::Tag v1.6.4 fails under PerlOnJava because the Module::Build-based build omits its declared plugin module from blib/lib.

The distribution source contains lib/AudioFile/Info/MP3/Tag.pm, and META.yml correctly provides AudioFile::Info::MP3::Tag, but after the PerlOnJava Build step the generated blib/lib contains AudioFile/Info/Build.pm and does not contain AudioFile/Info/MP3/Tag.pm.

Evidence

• CPAN run: 20260918-141920-96054
• Distribution: AudioFile::Info::MP3::Tag v1.6.4
• System Perl: PASS, 4 files and 25 tests
• PerlOnJava: FAIL, 3/4 test programs and 2/6 reported subtests

The PerlOnJava failure is:

Can't locate object method "new" via package "AudioFile::Info::MP3::Tag"

It occurs in AudioFile::Info::Info.pm while the plugin-backed tests are trying to construct the MP3 handler. The same missing plugin also causes both POD-coverage checks to report that requiring AudioFile::Info::MP3::Tag failed.

The source package has:

lib/AudioFile/Info/MP3/Tag.pm

but the resulting build tree contains only:

blib/lib/AudioFile/Info/Build.pm

and no blib/lib/AudioFile/Info/MP3/Tag.pm.

Reproduction

Run the CPAN test for AudioFile::Info::MP3::Tag v1.6.4 with PerlOnJava. The dependency builds complete, including AudioFile::Info and MP3::Tag, but the final Build test fails in t/1_read.t, t/2_write.t, and t/4_pod_coverage.t because the plugin is not available from the build output.

The relevant build output reports AudioFile::Info-MP3-Tag as built successfully, despite the missing module file.

Expected behavior

A successful Module::Build build must copy every declared Perl module from lib/ into the corresponding blib/lib/ path. In this case it should produce:

blib/lib/AudioFile/Info/MP3/Tag.pm

The subsequent test environment should then be able to load the plugin and run the 25 tests successfully, matching system Perl.

Requested fix

Investigate PerlOnJava's Module::Build file-discovery or staging logic for nested module paths and ensure that ordinary declared pure-Perl modules are copied into blib/lib during Build.

Add focused regression coverage that verifies a nested module such as AudioFile::Info::MP3::Tag is present in blib/lib after a Module::Build build, then rerun the distribution's test suite.

Related issues

• Related to #1294, which tracks missing generated pure-Perl modules in XS fallback builds. This report concerns an ordinary source module that is present in lib/ but omitted from blib/lib.
• Related to #1372, which tracks missing MakeMaker pm_to_blib build markers. This report concerns the module staging result itself rather than the marker file.