Fix HTML::Template::Compiled global variables and warning metadata #1382

Summary

HTML::Template::Compiled 1.003 passes its upstream test suite under system Perl but fails under PerlOnJava in two functional areas: global-variable/include rendering and warning plus source-line metadata propagation.

CPAN evidence

CPAN random tester run 20260915-094334-6702:

• Distribution: HTML-Template-Compiled 1.003
• System Perl: complete suite passes; 38 test files, 259 executed tests
• PerlOnJava: 9 of 262 executed assertions fail across 2 of 38 test programs
• Build and dependency setup complete successfully
• Dependency: Parse::RecDescent 1.967015 builds and passes its own tests

The PerlOnJava failures are:

t/08_global_vars.t ............. 1 failure
t/39_line_info.t ............... 8 failures

The other 36 test programs pass, including template parameters, filters, includes, loops, expressions, encoding, plugins, precompilation, and POD-related tests.

Failure 1: global variable and include rendering

t/08_global_vars.t creates a template with global_vars => 1, a loop containing local values, and an included template that references a global value. System Perl renders the expected loop values and global values. PerlOnJava produces an empty result, causing the global_vars assertion to fail.

The test also covers an unset-variable control case and a separate global_vars => 2 nested tmpl_with case; those assertions pass. The failing behavior is therefore narrower than all global-variable or nested-scope handling.

Expected output includes:

loopvar: one ... global: 42 ... included: ...
loopvar: two ... global: 23 ... included: ...
loopvar: three ... global: 42 ... included: ...

Observed PerlOnJava output for the main assertion is empty.

Failure 2: warnings and template source line information

t/39_line_info.t renders a template containing an undefined value under three warning modes: disabled, enabled, and fatal. It runs each mode with line_info => 0 and line_info => 1.

The expected behavior under system Perl is:

• warnings => 0: no warning and normal output
• warnings => 1: an Use of uninitialized value warning
• warnings => fatal: empty output and a fatal exception
• with line_info => 1, warning and exception text identifies t.templates.line_info1.html line 4

Under PerlOnJava:

• expected warnings are absent
• warnings => fatal does not stop output
• expected source-line metadata is absent

This produces 8 failed assertions in the test.

Suspected ownership

The failures are pure-Perl compatibility defects attributable to PerlOnJava. The exact ownership should be reduced before implementation:

1. For global_vars, inspect template include execution, scope lookup, and output-buffer control flow for the main global_vars => 1 loop path.
2. For t/39_line_info.t, inspect warning-category emission, fatal-warning conversion, localized warning handlers, and propagation of template source locations through generated/evaluated code.
3. Compare JVM and interpreter backends and determine whether either symptom is shared runtime behavior or backend-specific.
4. Confirm whether the two symptoms share a scope/evaluation or generated-code cause; do not assume they are one defect solely because they occur in the same distribution.

This is not a missing service, platform prerequisite, timeout, or native/XS failure.

Regression coverage and acceptance criteria

• Add a project-owned, system-Perl-validated regression for the smallest global_vars => 1 include/loop case that reproduces the empty output.
• Add focused coverage for warning-disabled, warning-enabled, and fatal-warning behavior with and without template line information.
• Preserve expected output, warning text, fatal behavior, and source location on both JVM and interpreter backends.
• Re-run the unchanged HTML::Template::Compiled 1.003 suite and require all available upstream tests to pass.
• Run the existing warning, scope, include, generated-code, and source-location tests to guard against regressions.

Related but distinct: #1377 concerns Log::Fine dynamic placeholders and caller metadata; it does not cover HTML::Template::Compiled global-variable rendering or warning behavior.