Support indirect-object method dispatch used by Set::IntSpan

[fglock]

Summary

Set::IntSpan 1.19 fails one upstream test under PerlOnJava because valid Perl indirect-object method syntax is resolved as a call to a nonexistent main:: subroutine.

Reproduction

Run the normal Set::IntSpan 1.19 test suite. The focused failure is t/real_set.t, which contains calls such as:

my $set_2 = union $set "1-5,8-9";
my $set_3 = union $set $set_2;
my $set_4 = union $set +[1, 5, 2, 8, 9, 1, 3, 4, 9];

These are valid Perl indirect-object method calls. The union method is implemented by Set::IntSpan and is used through the object in $set.

Expected result

System Perl passes the complete upstream suite:

• 20 test files
• 1,947 tests
• t/real_set.t passes all 4 tests

Actual result

PerlOnJava runs the first real_set.t operation successfully, then fails at the next indirect method call:

1..4
#real_set
#real_set:  union set -> -
ok 1
Undefined subroutine &main::union called at t/real_set.t line 22.

The archived CPAN run records:

Failed 1/20 test programs. 0/1944 subtests failed.

The focused t/real_set.t failure reproduces on both the JVM and interpreter backends.

Likely root cause

The parser/compiler recognizes the first form, union $set, sufficiently to execute the empty-set case, but does not consistently preserve the indirect-object method dispatch when additional arguments follow. It emits or resolves union as an ordinary bareword subroutine call in the main package instead of dispatching it as a method on $set.

This is a pure-Perl parser/runtime compatibility issue. Set::IntSpan contains no XS, C, XSLoader, DynaLoader, or FFI dependency, and the failure is independent of services or platform prerequisites.

Acceptance criteria

• All indirect-object method forms used by Set::IntSpan t/real_set.t dispatch to the object method on both backends.
• Set::IntSpan 1.19 passes all 1,947 upstream tests on JVM and interpreter backends.
• Add project-owned regression coverage for an indirect method call with no extra argument, a string argument, an object argument, and an array-reference argument.
• Preserve existing parsing behavior for ordinary bareword subroutine calls and malformed syntax.

Evidence

• CPAN run: 20260918-141920-96054
• Distribution: Set-IntSpan-1.19
• Failing test: t/real_set.t, line 22 (union $set "1-5,8-9")
• System Perl: PASS, 20 files / 1,947 tests
• PerlOnJava: FAIL, 1 file; the run reached 1,944 tests before aborting
• JVM and interpreter: focused failure reproduced

Related issues

• #1166 tracks valid fully-qualified indirect-object constructor forms. It covers a related parser area, but not this unqualified indirect-object method dispatch form.
• #1314 tracks bareword filehandle method dispatch used by Expect. It is related at the method-dispatch level, but this failure involves a normal Perl object and does not depend on filehandle or IO behavior.

This issue should be coordinated with those parser/runtime fixes, while retaining Set::IntSpan as independent regression coverage.