[flang] Dial some errors down to warnings for ASSOCIATED()

[klausler]

Summary

When a procedure pointer is associated with a procedure target, f18
will emit hard error messages if the pointer is incompatible with the
target in a way that would cause the program to not work if the
procedure pointer were actually called. However, in the context of
the ASSOCIATED() intrinsic, the compiler should not consider a query
to be a compilation-time error if the pointer and the target are
incompatible. The standard gives us sufficient wiggle room here
to treat these cases as warnings.

Attempts to use ASSOCIATED to test whether a procedure pointer is
associated with a data object, or vice versa, remain errors.

[jeanPerier]

LGTM

flang/lib/Evaluate/intrinsics.cpp

if (const auto *pointerExpr{pointerArg->UnwrapExpr()}) {
               }
               if (pointerProc) {
                 if (targetProc) {
                   // procedure pointer and procedure target
                   std::string whyNot;
                   if (std::optional<parser::MessageFixedText> msg{
                           CheckProcCompatibility(
                               isCall, pointerProc, &*targetProc, whyNot)}) {
+                    msg->set_severity(parser::Severity::Warning);
                     AttachDeclaration(
                         context.messages().Say(std::move(*msg),
                             "pointer '" + pointerSymbol->name().ToString() +
                                 "'",
                             targetName, whyNot),
                         *pointerSymbol);
                   }
                 } else {

flang/test/Semantics/associated.f90

subroutine test()
     lvar = associated (intPointerVar1, null(intPointerVar1)) ! ok
 
     !ERROR: In assignment to procedure pointer 'intprocpointer1', the target is not a procedure or procedure pointer
     intprocPointer1 => intVar
     !ERROR: POINTER= argument 'intprocpointer1' is a procedure pointer but the TARGET= argument 'intvar' is not a procedure or procedure pointer
     lVar = associated(intprocPointer1, intVar)
     !ERROR: Procedure pointer 'intprocpointer1' associated with incompatible procedure designator 'elementalproc': incompatible dummy argument #1: incompatible dummy data object attributes
     intProcPointer1 => elementalProc
-    !ERROR: Procedure pointer 'intprocpointer1' associated with incompatible procedure designator 'elementalproc': incompatible dummy argument #1: incompatible dummy data object attributes
+    !WARNING: Procedure pointer 'intprocpointer1' associated with incompatible procedure designator 'elementalproc': incompatible dummy argument #1: incompatible dummy data object attributes
     lvar = associated(intProcPointer1, elementalProc)
     !ERROR: POINTER= argument 'intpointervar1' is an object pointer but the TARGET= argument 'intfunc' is a procedure designator
     lvar = associated (intPointerVar1, intFunc)
     !ERROR: In assignment to object pointer 'intpointervar1', the target 'intfunc' is a procedure designator
     intPointerVar1 => intFunc
     !ERROR: In assignment to procedure pointer 'intprocpointer1', the target is not a procedure or procedure pointer
     intProcPointer1 => targetIntVar1
     !ERROR: POINTER= argument 'intprocpointer1' is a procedure pointer but the TARGET= argument 'targetintvar1' is not a procedure or procedure pointer
     lvar = associated (intProcPointer1, targetIntVar1)
     !ERROR: Procedure pointer 'intprocpointer1' associated with result of reference to function 'null' that is an incompatible procedure pointer: function results have incompatible types: INTEGER(4) vs REAL(4)
     intProcPointer1 => null(mold=realProcPointer1)
-    !ERROR: Procedure pointer 'intprocpointer1' associated with result of reference to function 'null()' that is an incompatible procedure pointer: function results have incompatible types: INTEGER(4) vs REAL(4)
+    !WARNING: Procedure pointer 'intprocpointer1' associated with result of reference to function 'null()' that is an incompatible procedure pointer: function results have incompatible types: INTEGER(4) vs REAL(4)
     lvar = associated(intProcPointer1, null(mold=realProcPointer1))
     !ERROR: PURE procedure pointer 'purefuncpointer' may not be associated with non-PURE procedure designator 'intproc'
     pureFuncPointer => intProc
-    !ERROR: PURE procedure pointer 'purefuncpointer' may not be associated with non-PURE procedure designator 'intproc'
+    !WARNING: PURE procedure pointer 'purefuncpointer' may not be associated with non-PURE procedure designator 'intproc'
     lvar = associated(pureFuncPointer, intProc)
     !ERROR: Procedure pointer 'realprocpointer1' associated with incompatible procedure designator 'intproc': function results have incompatible types: REAL(4) vs INTEGER(4)
     realProcPointer1 => intProc
-    !ERROR: Procedure pointer 'realprocpointer1' associated with incompatible procedure designator 'intproc': function results have incompatible types: REAL(4) vs INTEGER(4)
+    !WARNING: Procedure pointer 'realprocpointer1' associated with incompatible procedure designator 'intproc': function results have incompatible types: REAL(4) vs INTEGER(4)
     lvar = associated(realProcPointer1, intProc)
     subProcPointer => externalProc ! OK to associate a procedure pointer  with an explicit interface to a procedure with an implicit interface
     lvar = associated(subProcPointer, externalProc) ! OK to associate a procedure pointer with an explicit interface to a procedure with an implicit interface
     !ERROR: Subroutine pointer 'subprocpointer' may not be associated with function designator 'intproc'
     subProcPointer => intProc
-    !ERROR: Subroutine pointer 'subprocpointer' may not be associated with function designator 'intproc'
+    !WARNING: Subroutine pointer 'subprocpointer' may not be associated with function designator 'intproc'
     lvar = associated(subProcPointer, intProc)
     !ERROR: Function pointer 'intprocpointer1' may not be associated with subroutine designator 'subproc'
     intProcPointer1 => subProc
-    !ERROR: Function pointer 'intprocpointer1' may not be associated with subroutine designator 'subproc'
+    !WARNING: Function pointer 'intprocpointer1' may not be associated with subroutine designator 'subproc'
     lvar = associated(intProcPointer1, subProc)
     implicitProcPointer => subr ! OK for an implicit point to point to an explicit proc
     lvar = associated(implicitProcPointer, subr) ! OK
-    !ERROR: Procedure pointer 'implicitprocpointer' with implicit interface may not be associated with procedure designator 'subrcannotbecalledfromimplicit' with explicit interface that cannot be called via an implicit interface
+    !WARNING: Procedure pointer 'implicitprocpointer' with implicit interface may not be associated with procedure designator 'subrcannotbecalledfromimplicit' with explicit interface that cannot be called via an implicit interface
     lvar = associated(implicitProcPointer, subrCannotBeCalledFromImplicit)
     !ERROR: Procedure pointer 'cannotbecalledfromimplicitpointer' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
     cannotBeCalledfromImplicitPointer => externalProc
-    !ERROR: Procedure pointer 'cannotbecalledfromimplicitpointer' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
+    !WARNING: Procedure pointer 'cannotbecalledfromimplicitpointer' with explicit interface that cannot be called via an implicit interface cannot be associated with procedure designator with an implicit interface
     lvar = associated(cannotBeCalledfromImplicitPointer, externalProc)
   end subroutine test
 end subroutine assoc