fix: preserve lvalue returns through goto markers

dev/design/issue-queue.md

@@ -1,6 +1,6 @@
 # Reviewed issue queues
 
-Snapshot: 2026-10-27, from live open issues, PRs and the #1649 phase contract.
+Snapshot: 2026-10-28, from live open issues, PRs and the #1649 phase contract.
 This is a bounded selection aid, not the complete backlog or fresh runtime
 validation. Follow the [triage and claim protocol](../../docs/guides/issue-triage.md)
 and recheck live issue comments/PRs before starting. Unlisted work is unreviewed
@@ -33,6 +33,7 @@ resolved before implementation. No new pass or failure is asserted here.
 | Frontend constants/quoting | [#1376](https://github.com/fglock/PerlOnJava/issues/1376) Constant hash-reference dereference | High / Investigate | Both-backend suite failures are reported. Minimize constant folding/dereference behavior and establish a failing current parent before selecting the fix. |
 | Parser syntax | [#1427](https://github.com/fglock/PerlOnJava/issues/1427) Test::Unit / Error.pm | Normal / Investigate | Separate catch-syntax behavior from example-path normalization; retain the full passing Perl comparison and identify independently fixable causes. |
 | Calls and value operations | [#1448](https://github.com/fglock/PerlOnJava/issues/1448) Audit-wrapper recursion | High / Investigate | Runaway recursion on both backends with a passing Perl suite. Trace captured original coderef identity and wrapper replacement under a timeout; no proven #1649 dependency. |
+| Lvalue return flow | [#1915](https://github.com/fglock/PerlOnJava/issues/1915) Undef aliases through `goto` | Normal / Active | [Draft PR #1917](https://github.com/fglock/PerlOnJava/pull/1917) is open; [current claim](https://github.com/fglock/PerlOnJava/issues/1915#issuecomment-6472368217) records the passing local gates and current CI run. |
 | Calls and value operations | [#1342](https://github.com/fglock/PerlOnJava/issues/1342) Relational overload dispatch | Normal / Ready | Report identifies an unwanted `cmp` dispatch. Add direct relational-overload coverage and require Morpheus acceptance on both backends. |
 | Calls and value operations | [#1428](https://github.com/fglock/PerlOnJava/issues/1428) Decimal stringification | Normal / Ready | One DateTime::Format::Epoch mismatch with passing Perl suite. Reduce the numeric conversion and cover large integral results without scientific notation. |
 | Warnings category tables | [#1208](https://github.com/fglock/PerlOnJava/issues/1208), [#1219](https://github.com/fglock/PerlOnJava/issues/1219) Experimental categories | Normal / Ready | Unknown valid categories prevent module load. Check shared registration code, add category-specific focused tests and upstream load acceptance; batch only if one registration mechanism owns both. |

docs/about/changelog.md

@@ -11,6 +11,7 @@ priorities and future plans.
 - Export `fieldhash` from `Hash::Util` for compatibility with core Perl.
 - Normalize tied-hash `exists` results to Perl's boolean values.
 
+- Preserve lvalue returns through `goto &sub` without validating the empty control-flow marker (#1915).
 - Preserve reference lifetime when overloaded `++` and `--` fall back to arithmetic (#1901).
 - Parse forward-declared qualified classes as indirect constructors inside `new` methods (#1899).
 

src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeCode.java

@@ -2171,6 +2171,12 @@ public static RuntimeScalar keysLvalue(RuntimeBase container) {
     }
 
     public static RuntimeList returnList(RuntimeBase retVal, int callContext, boolean copyReferenceScalars) {
+        // A control-flow marker has not produced a Perl return value yet. In
+        // particular, goto &sub must reach its replacement subroutine before
+        // lvalue-return validation; the marker itself is intentionally empty.
+        if (retVal instanceof RuntimeControlFlowList) {
+            return (RuntimeList) retVal;
+        }
         requireWritableLvalueReturn(callContext, retVal);
         if (retVal == null) {
             requireNonemptyLvalueReturn(callContext, null);

src/test/resources/unit/lvalue_sub_goto_undef_alias.t

@@ -0,0 +1,28 @@
+use strict;
+use warnings;
+use Test::More;
+
+my $slot;
+
+sub lvalue_target :lvalue {
+    $slot;
+}
+
+lvalue_target() = 'direct';
+is($slot, 'direct', 'lvalue sub returns a writable undef slot');
+
+undef $slot;
+sub lvalue_goto_wrapper :lvalue {
+    goto &lvalue_target;
+}
+
+lvalue_goto_wrapper() = 'assigned';
+is($slot, 'assigned', 'goto lvalue wrapper forwards a writable undef slot');
+
+sub empty_lvalue_return :lvalue {}
+my $error;
+eval { empty_lvalue_return() = 'replacement'; 1 } or $error = $@;
+like($error, qr/^Can't return undef from lvalue subroutine/,
+    'empty lvalue return remains invalid');
+
+done_testing;