[flang] Take character function length into account when testing compatibility

[klausler]

Summary

When a character-valued function is passed as an actual argument, and both
the actual function and the dummy argument have explicit result lengths, take them
into account when testing for compatibility.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Evaluate/characteristics.cpp

if (const auto *actualTypeShape{std::get_if<TypeAndShape>(&actual.u)}) {
           *whyNot = "function results have distinct ranks";
         }
       } else if (!attrs.test(Attr::Allocatable) && !attrs.test(Attr::Pointer) &&
           !AreCompatibleFunctionResultShapes(
               ifaceTypeShape->shape(), actualTypeShape->shape())) {
         if (whyNot) {
           *whyNot = "function results have distinct constant extents";
         }
-      } else if (!ifaceTypeShape->type().IsTkCompatibleWith(
+      } else if (!ifaceTypeShape->type().IsTkLenCompatibleWith(
                      actualTypeShape->type())) {
         if (whyNot) {
           *whyNot = "function results have incompatible types: "s +
               ifaceTypeShape->type().AsFortran() + " vs "s +
               actualTypeShape->type().AsFortran();
         }
       } else {
         return true;

flang/test/Semantics/call25.f90

 ! RUN: not %flang -fsyntax-only 2>&1 %s | FileCheck %s
 module m
  contains
   subroutine subr1(f)
     character(5) f
     print *, f('abcde')
   end subroutine
   subroutine subr2(f)
     character(*) f
     print *, f('abcde')
   end subroutine
   character(5) function explicitLength(x)
     character(5), intent(in) :: x
     explicitLength = x
   end function
+  character(6) function badExplicitLength(x)
+    character(5), intent(in) :: x
+    badExplicitLength = x
+  end function
   real function notChar(x)
     character(*), intent(in) :: x
     notChar = 0
   end function
 end module
 
 character(*) function assumedLength(x)
   character(*), intent(in) :: x
   assumedLength = x
 end function
 
 subroutine subr3(f)
   character(5) f
   print *, f('abcde')
 end subroutine
 
 program main
   use m
   external assumedlength
   character(5) :: assumedlength
   call subr1(explicitLength)
+  !CHECK: error: Actual argument function associated with procedure dummy argument 'f=' has incompatible result type
+  call subr1(badExplicitLength)
   call subr1(assumedLength)
   !CHECK: error: Actual argument function associated with procedure dummy argument 'f=' has incompatible result type
   call subr1(notChar)
   call subr2(explicitLength)
   call subr2(assumedLength)
   !CHECK: error: Actual argument function associated with procedure dummy argument 'f=' has incompatible result type
   call subr2(notChar)
   call subr3(explicitLength)
+  !CHECK: warning: If the procedure's interface were explicit, this reference would be in error
+  !CHECK: because: Actual argument function associated with procedure dummy argument 'f=' has incompatible result type
+  call subr3(badExplicitLength)
   call subr3(assumedLength)
   !CHECK: warning: If the procedure's interface were explicit, this reference would be in error
   !CHECK: because: Actual argument function associated with procedure dummy argument 'f=' has incompatible result type
   call subr3(notChar)
 end program