[flang] Foil attempt to READ a NAMELIST with an undefinable member

[klausler]

Summary

Detect and emit errors about undefinable NAMELIST group members in READ statements.

Fixes llvm-test-suite/Fortran/gfortran/regression/namelist_2.f90.

flang/lib/Semantics/check-io.cpp

if (auto *msg{CheckForBadIoType(*type, which, where)}) {
       return msg;
     }
   }
   return nullptr;
 }
 
 void IoChecker::CheckNamelist(const Symbol &namelist, common::DefinedIo which,
     parser::CharBlock namelistLocation) const {
+  if (!context_.HasError(namelist)) {
     const auto &details{namelist.GetUltimate().get<NamelistDetails>()};
     for (const Symbol &object : details.objects()) {
       context_.CheckIndexVarRedefine(namelistLocation, object);
       if (auto *msg{CheckForBadIoType(object, which, namelistLocation)}) {
         evaluate::AttachDeclaration(*msg, namelist);
+      } else if (which == common::DefinedIo::ReadFormatted) {
+        if (auto why{WhyNotDefinable(namelistLocation, namelist.owner(),
+                DefinabilityFlags{}, object)}) {
+          context_
+              .Say(namelistLocation,
+                  "NAMELIST input group must not contain undefinable item '%s'"_err_en_US,
+                  object.name())
+              .Attach(std::move(*why));
+          context_.SetError(namelist);
+        }
+      }
     }
   }
 }
 
 } // namespace Fortran::semantics

flang/lib/Semantics/resolve-names.cpp

for (const parser::NamelistStmt::Group *group : deferred->namelistGroups) {
         if (auto *details{groupSymbol->detailsIf<NamelistDetails>()}) {
           for (const auto &name : std::get<std::list<parser::Name>>(group->t)) {
             auto *symbol{FindSymbol(name)};
             if (!symbol) {
               symbol = &MakeSymbol(name, ObjectEntityDetails{});
               ApplyImplicitRules(*symbol);
             } else if (!ConvertToObjectEntity(*symbol)) {
               SayWithDecl(name, *symbol, "'%s' is not a variable"_err_en_US);
+              context().SetError(*groupSymbol);
             }
             symbol->GetUltimate().set(Symbol::Flag::InNamelist);
             details->add_object(*symbol);
           }
         }
       }
     }
     deferred->namelistGroups.clear();

flang/test/Semantics/resolve40.f90

subroutine s11
   integer :: nl2
   !ERROR: 'nl2' is already declared in this scoping unit
   namelist /nl2/x
   namelist /nl3/x
   !ERROR: 'nl3' is already declared in this scoping unit
   integer :: nl3
   nl2 = 1
 end
+
+subroutine s12(x)
+  real, intent(in) :: x
+  namelist /nl/x
+  !ERROR: NAMELIST input group must not contain undefinable item 'x'
+  !BECAUSE: 'x' is an INTENT(IN) dummy argument
+  read(*,nml=nl)
+end