[flang][runtime] Handle null list-directed fields in child input (#155707)

List-directed input statements maintain two flags ("eatComma_" and
"hitSlash_") in their state that allow GetNextDataEdit() to detect and
handle field separators (usually ',') and slashes in the input stream.
For list-directed input in a defined input subroutine, it's necessary to
copy those flags from the parent list-directed input statement (if any)
and update them afterwards.

Fixes https://github.com/llvm/llvm-project/issues/154791.

1 files changed, 2 insertions, 0 deletions

diff --git a/flang-rt/lib/runtime/descriptor-io.cpp b/flang-rt/lib/runtime/descriptor-io.cpp
index a60d0b90da46..668190febf39 100644
--- a/flang-rt/lib/runtime/descriptor-io.cpp
+++ b/flang-rt/lib/runtime/descriptor-io.cpp
@@ -170,6 +170,8 @@ static RT_API_ATTRS Fortran::common::optional<bool> DefinedFormattedIo(
       io.GotChar(io.InquirePos() - *startPos);
     }
     return handler.GetIoStat() == IostatOk;
+  } else if (peek && peek->descriptor == DataEdit::ListDirectedNullValue) {
+    return false;
   } else {
     // There's a defined I/O subroutine, but there's a FORMAT present and
     // it does not have a DT data edit descriptor, so apply default formatting