[flang] Set the addendum when establishing pointer section in descriptor

[jeanPerier]

Summary

If the source has an addendum, the descriptor that is being established
to describe a section over the source needs to copy the addendum so that
derived type information is correctly set in the descriptor being
established.

This allows namelist IO with derived type to work correctly.

[schweitz]

+1

[klausler]

Thank you so much for finding this!

flang/runtime/descriptor.cpp

244

Please use braced initialization here in the runtime, and you can put the auto *addendum{Addendum()} into the if statement.

[jeanPerier]

Use flang coding style.

flang/runtime/descriptor.cpp

if (!stride || stride[j] == 0) {
       if (newRank > 0) {
         --newRank;
       } else {
         return false;
       }
     }
   }
   raw_.rank = newRank;
+  if (const auto *sourceAddendum = source.Addendum()) {
+    if (auto *addendum{Addendum()}) {
+      *addendum = *sourceAddendum;
+    } else {
+      return false;
+    }
+  }
   return CFI_section(&raw_, &source.raw_, lower, upper, stride) == CFI_SUCCESS;
 }
 
 void Descriptor::Check() const {
   // TODO
 }
 
 void Descriptor::Dump(FILE *f) const {