From 76478da82251a5fbcc4aa8f387b450c172613e6d Mon Sep 17 00:00:00 2001
From: "Flavio S. Glock" <flavio.glock@booking.com>
Date: Fri, 30 Oct 2026 12:01:03 +0100
Subject: [PATCH] fix: preserve input line context across borrowed handle scope

Keep the last-read handle active when JVM scope cleanup sees a temporary alias
of an anonymous IO glob that still has a live owner. This preserves Perl's `$.`
and IO::Handle->input_line_number behavior through wrapper subroutines.

Add focused coverage for scalar-backed IO::Handle reads and record the fix in
the work-in-progress changelog. Fixes #1933.

Generated with [Codex](https://openai.com/codex)

Co-Authored-By: Codex <codex@openai.com>
---
 docs/about/changelog.md                       |  2 ++
 .../runtime/runtimetypes/RuntimeScalar.java   | 12 +++++++++--
 .../unit/io_handle_input_line_number.t        | 21 +++++++++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 src/test/resources/unit/io_handle_input_line_number.t

diff --git a/docs/about/changelog.md b/docs/about/changelog.md
index 6fe3d8dde5..82c18de71a 100644
--- a/docs/about/changelog.md
+++ b/docs/about/changelog.md
@@ -6,6 +6,8 @@ priorities and future plans.
 
 ## Work in progress
 
+- Preserve the input line number when a borrowed anonymous filehandle alias leaves a JVM subroutine scope (#1933).
+
 - Resolve glob-backed filehandles in `POSIX::isatty` without assuming the glob value is a `RuntimeIO` (#1932).
 
 - Add an initial CryptX Java XS bridge for binary/base64url helpers, functional digests, and HMAC using the existing JCA and Bouncy Castle providers (#1220).
diff --git a/src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeScalar.java b/src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeScalar.java
index b2eabcdf5b..d45c22c80e 100644
--- a/src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeScalar.java
+++ b/src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeScalar.java
@@ -5201,8 +5201,16 @@ public static void scopeExitCleanup(RuntimeScalar scalar) {
             RuntimeIO last = RuntimeIO.getLastAccessedHandle();
             if ((glob.globName != null && glob.globName.equals(last.globName))
                     || (glob.IO != null && glob.IO.value == last)) {
-                RuntimeIO.setLastAccessedHandle(null);
-                RuntimeIO.setLastReadlineHandleName(null);
+                // A borrowed anonymous handle alias can leave scope while the
+                // caller still owns the same IO glob. Keep its $. context until
+                // that durable owner leaves; clearing on the borrow breaks
+                // getline/input_line_number calls inside wrapper subroutines.
+                boolean borrowedLiveIo = isUnstashedIoGlob(glob)
+                        && !scalar.ioOwner && glob.ioHolderCount > 0;
+                if (!borrowedLiveIo) {
+                    RuntimeIO.setLastAccessedHandle(null);
+                    RuntimeIO.setLastReadlineHandleName(null);
+                }
             }
         }
 
diff --git a/src/test/resources/unit/io_handle_input_line_number.t b/src/test/resources/unit/io_handle_input_line_number.t
new file mode 100644
index 0000000000..b4c92e5f84
--- /dev/null
+++ b/src/test/resources/unit/io_handle_input_line_number.t
@@ -0,0 +1,21 @@
+use strict;
+use warnings;
+use Test::More;
+use IO::Handle;
+
+my $input = "first\nsecond\n";
+open my $fh, '<', \$input or die "open scalar handle: $!";
+
+is($fh->getline, "first\n", 'read the first line from a scalar handle');
+is($., 1, 'the global input line number follows getline');
+my $read_line_number = sub { $. };
+is($read_line_number->(), 1,
+    'the global input line number is visible inside a subroutine');
+is($fh->input_line_number, 1,
+    'input_line_number reports the current line after getline');
+
+is($fh->getline, "second\n", 'read the second line from a scalar handle');
+is($fh->input_line_number, 2,
+    'input_line_number advances with subsequent getline calls');
+
+done_testing;