From 9a7a16c8d5a5927bfadd05e01c288a4fada00830 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler@nvidia.com>
Date: Mon, 18 Aug 2025 14:44:48 -0700
Subject: [PATCH] [flang][runtime] Allow child NAMELIST input to advance
 records (#153963)

NAMELIST input in child I/O is rare, and it's not clear in the standard
whether it should be allowed to advance to later records in the parent
unit. But GNU Fortran supports it, and there's no good reason not to do
so since a NAMELIST input group that isn't terminated on the same line
is otherwise going to be a fatal error.

Fixes https://github.com/llvm/llvm-project/issues/153416.
---
 flang-rt/include/flang-rt/runtime/io-stmt.h |  1 +
 flang-rt/lib/runtime/io-stmt.cpp            | 20 +++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/flang-rt/include/flang-rt/runtime/io-stmt.h b/flang-rt/include/flang-rt/runtime/io-stmt.h
index 7693b60cccfc..3d1ca5091e92 100644
--- a/flang-rt/include/flang-rt/runtime/io-stmt.h
+++ b/flang-rt/include/flang-rt/runtime/io-stmt.h
@@ -696,6 +696,7 @@ public:
   RT_API_ATTRS ChildListIoStatementState(
       ChildIo &, const char *sourceFile = nullptr, int sourceLine = 0);
   using ListDirectedStatementState<DIR>::GetNextDataEdit;
+  RT_API_ATTRS bool AdvanceRecord(int = 1);
   RT_API_ATTRS int EndIoStatement();
 };
 
diff --git a/flang-rt/lib/runtime/io-stmt.cpp b/flang-rt/lib/runtime/io-stmt.cpp
index c462f60b6b01..28149090eb16 100644
--- a/flang-rt/lib/runtime/io-stmt.cpp
+++ b/flang-rt/lib/runtime/io-stmt.cpp
@@ -1106,10 +1106,14 @@ ChildListIoStatementState<DIR>::ChildListIoStatementState(
 }
 
 template <Direction DIR>
-bool ChildUnformattedIoStatementState<DIR>::Receive(
-    char *data, std::size_t bytes, std::size_t elementBytes) {
+bool ChildListIoStatementState<DIR>::AdvanceRecord(int n) {
 #if !defined(RT_DEVICE_AVOID_RECURSION)
-  return this->child().parent().Receive(data, bytes, elementBytes);
+  // Allow child NAMELIST input to advance
+  if (DIR == Direction::Input && this->mutableModes().inNamelist) {
+    return this->child().parent().AdvanceRecord(n);
+  } else {
+    return false;
+  }
 #else
   this->ReportUnsupportedChildIo();
 #endif
@@ -1125,6 +1129,16 @@ template <Direction DIR> int ChildListIoStatementState<DIR>::EndIoStatement() {
   return ChildIoStatementState<DIR>::EndIoStatement();
 }
 
+template <Direction DIR>
+bool ChildUnformattedIoStatementState<DIR>::Receive(
+    char *data, std::size_t bytes, std::size_t elementBytes) {
+#if !defined(RT_DEVICE_AVOID_RECURSION)
+  return this->child().parent().Receive(data, bytes, elementBytes);
+#else
+  this->ReportUnsupportedChildIo();
+#endif
+}
+
 template class InternalIoStatementState<Direction::Output>;
 template class InternalIoStatementState<Direction::Input>;
 template class InternalFormattedIoStatementState<Direction::Output>;