[flang] Catch attempts to do anything with statement functions other than call them

A statement function in Fortran may be called, but it may not be the target
of a procedure pointer or passed as an actual argument.

flang/lib/Semantics/check-call.cpp

@@ -77,13 +77,21 @@ static void CheckImplicitInterfaceArg(evaluate::ActualArgument &arg,
                    "actual argument", *expr, context)}) {
       const auto *argProcDesignator{
           std::get_if<evaluate::ProcedureDesignator>(&expr->u)};
-      const auto *argProcSymbol{
-          argProcDesignator ? argProcDesignator->GetSymbol() : nullptr};
-      if (argProcSymbol && !argChars->IsTypelessIntrinsicDummy() &&
-          argProcDesignator && argProcDesignator->IsElemental()) { // C1533
+      if (const auto *argProcSymbol{
+              argProcDesignator ? argProcDesignator->GetSymbol() : nullptr}) {
+        if (!argChars->IsTypelessIntrinsicDummy() && argProcDesignator &&
+            argProcDesignator->IsElemental()) { // C1533
           evaluate::SayWithDeclaration(messages, *argProcSymbol,
               "Non-intrinsic ELEMENTAL procedure '%s' may not be passed as an actual argument"_err_en_US,
               argProcSymbol->name());
+        } else if (const auto *subp{argProcSymbol->GetUltimate()
+                                        .detailsIf<SubprogramDetails>()}) {
+          if (subp->stmtFunction()) {
+            evaluate::SayWithDeclaration(messages, *argProcSymbol,
+                "Statement function '%s' may not be passed as an actual argument"_err_en_US,
+                argProcSymbol->name());
+          }
+        }
       }
     }
   }
@@ -574,6 +582,17 @@ static void CheckProcedureArg(evaluate::ActualArgument &arg,
         std::get_if<evaluate::ProcedureDesignator>(&expr->u)};
     const auto *argProcSymbol{
         argProcDesignator ? argProcDesignator->GetSymbol() : nullptr};
+    if (argProcSymbol) {
+      if (const auto *subp{
+              argProcSymbol->GetUltimate().detailsIf<SubprogramDetails>()}) {
+        if (subp->stmtFunction()) {
+          evaluate::SayWithDeclaration(messages, *argProcSymbol,
+              "Statement function '%s' may not be passed as an actual argument"_err_en_US,
+              argProcSymbol->name());
+          return;
+        }
+      }
+    }
     if (auto argChars{characteristics::DummyArgument::FromActual(
             "actual argument", *expr, context)}) {
       if (!argChars->IsTypelessIntrinsicDummy()) {

flang/lib/Semantics/pointer-assignment.cpp

@@ -279,6 +279,17 @@ bool PointerAssignmentChecker::Check(parser::CharBlock rhsName, bool isCall,
 }
 
 bool PointerAssignmentChecker::Check(const evaluate::ProcedureDesignator &d) {
+  if (const Symbol * symbol{d.GetSymbol()}) {
+    if (const auto *subp{
+            symbol->GetUltimate().detailsIf<SubprogramDetails>()}) {
+      if (subp->stmtFunction()) {
+        evaluate::SayWithDeclaration(context_.messages(), *symbol,
+            "Statement function '%s' may not be the target of a pointer assignment"_err_en_US,
+            symbol->name());
+        return false;
+      }
+    }
+  }
   if (auto chars{Procedure::Characterize(d, context_)}) {
     return Check(d.GetName(), false, &*chars, d.GetSpecificIntrinsic());
   } else {

flang/test/Semantics/assign03.f90

@@ -314,4 +314,11 @@ contains
     ptr => s_external
     call ptr
   end subroutine
+
+  subroutine s14
+    procedure(real), pointer :: ptr
+    sf(x) = x + 1.
+    !ERROR: Statement function 'sf' may not be the target of a pointer assignment
+    ptr => sf
+  end subroutine
 end

flang/test/Semantics/call02.f90

@@ -43,6 +43,19 @@ subroutine s02
   end function
 end
 
+subroutine s03
+  interface
+    subroutine sub1(p)
+      procedure(real) :: p
+    end subroutine
+  end interface
+  sf(x) = x + 1.
+  !ERROR: Statement function 'sf' may not be passed as an actual argument
+  call sub1(sf)
+  !ERROR: Statement function 'sf' may not be passed as an actual argument
+  call sub2(sf)
+end
+
 module m01
   procedure(sin) :: elem01
   interface