[flang] Runtime: Reset list-directed input state for each NAMELIST item

[klausler]

Summary

NAMELIST I/O formatting uses the runtime infrastructure for
list-directed I/O. List-directed input processing has same state
that requires reinitialization for each successive NAMELIST input
item. This patch fixes bugs with "null" items and repetition counts
on NAMELIST input items after the first in the group.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/runtime/io-stmt.h

class ListDirectedStatementState<Direction::Input>
     : public FormattedIoStatementState {
 public:
   // Skips value separators, handles repetition and null values.
   // Vacant when '/' appears; present with descriptor == ListDirectedNullValue
   // when a null value appears.
   std::optional<DataEdit> GetNextDataEdit(
       IoStatementState &, int maxRepeat = 1);
 
+  // Each NAMELIST input item is a distinct "list-directed"
+  // input statement.  This member function resets this state
+  // so that repetition and null values work correctly for each
+  // successive NAMELIST input item.
+  void ResetForNextNamelistItem() {
+    remaining_ = 0;
+    isFirstItem_ = true;
+    realPart_ = imaginaryPart_ = false;
+  }
+
 private:
   int remaining_{0}; // for "r*" repetition
   std::int64_t initialRecordNumber_;
   std::int64_t initialPositionInRecord_;
   bool isFirstItem_{true}; // leading separator implies null first item
   bool hitSlash_{false}; // once '/' is seen, nullify further items
   bool realPart_{false};
   bool imaginaryPart_{false};

flang/runtime/namelist.cpp

 }
 
 bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
   IoStatementState &io{*cookie};
   io.CheckFormattedStmtType<Direction::Input>("InputNamelist");
   ConnectionState &connection{io.GetConnectionState()};
   connection.modes.inNamelist = true;
   IoErrorHandler &handler{io.GetIoErrorHandler()};
+  auto *listInput{io.get_if<ListDirectedStatementState<Direction::Input>>()};
+  RUNTIME_CHECK(handler, listInput != nullptr);
   // Check the group header
   std::optional<char32_t> next{io.GetNextNonBlank()};
   if (!next || *next != '&') {
     handler.SignalError(
         "NAMELIST input group does not begin with '&' (at '%lc')", *next);
     return false;
   }
   io.HandleRelativePosition(1);
while (true) {
     next = io.GetNextNonBlank();
     if (!next || *next != '=') {
       handler.SignalError("No '=' found after item '%s' in NAMELIST group '%s'",
           name, group.groupName);
       return false;
     }
     io.HandleRelativePosition(1);
     // Read the values into the descriptor
+    listInput->ResetForNextNamelistItem();
     if (!descr::DescriptorIO<Direction::Input>(io, *useDescriptor)) {
       return false;
     }
     next = io.GetNextNonBlank();
     if (next && *next == ',') {
       io.HandleRelativePosition(1);
     }
   }