[flang-commits] [flang] [flang][runtime] Don't write implied ENDFILE for REC=/POS= (PR #79637)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/79637

An implied ENDFILE record, which truncates an external file, should be written to a sequential unit whenever the file is repositioned for a BACKSPACE or REWIND statement if a WRITE statement has executed since the last OPEN/BACKSPACE/REWIND.

But the REC= and POS= positioning specifiers don't apply to sequential units (they're for direct and stream units, resp.), so don't truncate the file when they're used.

>From d03b819b892cf28db1c0edea984e895e0c889f52 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Fri, 26 Jan 2024 11:06:31 -0800
Subject: [PATCH] [flang][runtime] Don't write implied ENDFILE for REC=/POS=

An implied ENDFILE record, which truncates an external file,
should be written to a sequential unit whenever the file is
repositioned for a BACKSPACE or REWIND statement if a WRITE
statement has executed since the last OPEN/BACKSPACE/REWIND.

But the REC= and POS= positioning specifiers don't apply to
sequential units (they're for direct and stream units, resp.),
so don't truncate the file when they're used.
---
 flang/runtime/unit.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/flang/runtime/unit.cpp b/flang/runtime/unit.cpp
index 18590567c65eb0a..d927d012225672d 100644
--- a/flang/runtime/unit.cpp
+++ b/flang/runtime/unit.cpp
@@ -679,6 +679,7 @@ void ExternalFileUnit::Rewind(IoErrorHandler &handler) {
     handler.SignalError(IostatRewindNonSequential,
         "REWIND(UNIT=%d) on non-sequential file", unitNumber());
   } else {
+    DoImpliedEndfile(handler);
     SetPosition(0, handler);
     currentRecordNumber = 1;
     leftTabLimit.reset();
@@ -687,7 +688,6 @@ void ExternalFileUnit::Rewind(IoErrorHandler &handler) {
 }
 
 void ExternalFileUnit::SetPosition(std::int64_t pos, IoErrorHandler &handler) {
-  DoImpliedEndfile(handler);
   frameOffsetInFile_ = pos;
   recordOffsetInFrame_ = 0;
   if (access == Access::Direct) {