[flang] runtime: catch OPEN(ACCESS='DIRECT',POSITION=)

[klausler]

Summary

A POSITION= specifier may not be used on a direct access file.

flang/runtime/io-api.cpp

   ConnectionState &connection{io.GetConnectionState()};
   if (connection.access != Access::Stream) {
     io.GetIoErrorHandler().SignalError(
-        "REC= may not appear unless ACCESS='STREAM'");
+        "POS= may not appear unless ACCESS='STREAM'");
     return false;
   }
   if (pos < 1) {

flang/runtime/io-stmt.h

 private:
   bool wasExtant_;
   std::optional<OpenStatus> status_;
-  Position position_{Position::AsIs};
+  std::optional<Position> position_;
   std::optional<Action> action_;
   Convert convert_{Convert::Native};
   OwningPtr<char> path_;

flang/runtime/io-stmt.cpp

 }
 
 int OpenStatementState::EndIoStatement() {
+  if (position_) {
+    if (access_ && *access_ == Access::Direct) {
+      SignalError("POSITION= may not be set with ACCESS='DIRECT'");
+      position_.reset();
+    }
+  }
   if (path_.get() || wasExtant_ ||
       (status_ && *status_ == OpenStatus::Scratch)) {
-    unit().OpenUnit(status_, action_, position_, std::move(path_), pathLength_,
-        convert_, *this);
+    unit().OpenUnit(status_, action_, position_.value_or(Position::AsIs),
+        std::move(path_), pathLength_, convert_, *this);
   } else {
-    unit().OpenAnonymousUnit(status_, action_, position_, convert_, *this);
+    unit().OpenAnonymousUnit(
+        status_, action_, position_.value_or(Position::AsIs), convert_, *this);
   }
   if (access_) {
     if (*access_ != unit().access) {
       if (wasExtant_) {
         SignalError("ACCESS= may not be changed on an open unit");
+        access_.reset();
       }
     }
-    unit().access = *access_;
+    if (access_) {
+      unit().access = *access_;
+    }
   }
   if (!unit().isUnformatted) {
     unit().isUnformatted = isUnformatted_;