[flang] Catch READ/WRITE on direct-access file without REC=

A data transfer statement must have REC= in its control list
if (and only if) the unit was opened with ACCESS='DIRECT'.
The runtime wasn't catching this error, but was just silently
advancing to the next record as if the access were sequential.

Differential Revision: https://reviews.llvm.org/D120838

2 files changed, 19 insertions, 1 deletions

diff --git a/flang/runtime/unit.cpp b/flang/runtime/unit.cpp
index 971909b74e76..6e6db7859278 100644
--- a/flang/runtime/unit.cpp
+++ b/flang/runtime/unit.cpp
@@ -310,6 +310,7 @@ bool ExternalFileUnit::Emit(const char *data, std::size_t bytes,
     handler.SignalError(IostatWriteAfterEndfile);
     return false;
   }
+  CheckDirectAccess(handler);
   WriteFrame(frameOffsetInFile_, recordOffsetInFrame_ + furthestAfter, handler);
   if (positionInRecord > furthestPositionInRecord) {
     std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord, ' ',
@@ -432,7 +433,7 @@ bool ExternalFileUnit::BeginReadingRecord(IoErrorHandler &handler) {
   if (!beganReadingRecord_) {
     beganReadingRecord_ = true;
     if (access == Access::Direct) {
-      RUNTIME_CHECK(handler, openRecl);
+      CheckDirectAccess(handler);
       auto need{static_cast<std::size_t>(recordOffsetInFrame_ + *openRecl)};
       auto got{ReadFrame(frameOffsetInFile_, need, handler)};
       if (got >= need) {
@@ -654,6 +655,9 @@ void ExternalFileUnit::SetPosition(std::int64_t pos, IoErrorHandler &handler) {
   DoImpliedEndfile(handler);
   frameOffsetInFile_ = pos;
   recordOffsetInFrame_ = 0;
+  if (access == Access::Direct) {
+    directAccessRecWasSet_ = true;
+  }
   BeginRecord();
 }
 
@@ -846,6 +850,17 @@ void ExternalFileUnit::CommitWrites() {
   BeginRecord();
 }
 
+bool ExternalFileUnit::CheckDirectAccess(IoErrorHandler &handler) {
+  if (access == Access::Direct) {
+    RUNTIME_CHECK(handler, openRecl);
+    if (!directAccessRecWasSet_) {
+      handler.SignalError("No REC= was specified for a data transfer with ACCESS='DIRECT'");
+      return false;
+    }
+  }
+  return true;
+}
+
 ChildIo &ExternalFileUnit::PushChildIo(IoStatementState &parent) {
   OwningPtr<ChildIo> current{std::move(child_)};
   Terminator &terminator{parent.GetIoErrorHandler()};
diff --git a/flang/runtime/unit.h b/flang/runtime/unit.h
index c8e65c1f0c4c..7be5e2f387f8 100644
--- a/flang/runtime/unit.h
+++ b/flang/runtime/unit.h
@@ -71,6 +71,7 @@ public:
     if constexpr (!std::is_same_v<A, OpenStatementState>) {
       state.mutableModes() = ConnectionState::modes;
     }
+    directAccessRecWasSet_ = false;
     io_.emplace(state);
     return *io_;
   }
@@ -112,11 +113,13 @@ private:
   void DoImpliedEndfile(IoErrorHandler &);
   void DoEndfile(IoErrorHandler &);
   void CommitWrites();
+  bool CheckDirectAccess(IoErrorHandler &);
 
   int unitNumber_{-1};
   Direction direction_{Direction::Output};
   bool impliedEndfile_{false}; // sequential/stream output has taken place
   bool beganReadingRecord_{false};
+  bool directAccessRecWasSet_{false}; // REC= appeared
 
   Lock lock_;