Fortran: function results never have the ALLOCATABLE attribute [PR109500]

Fortran 2018 8.5.3 (ALLOCATABLE attribute) explains in Note 1 that the
result of referencing a function whose result variable has the ALLOCATABLE
attribute is a value that does not itself have the ALLOCATABLE attribute.

gcc/fortran/ChangeLog:

	PR fortran/109500
	* interface.cc (gfc_compare_actual_formal): Reject allocatable
	functions being used as actual argument for allocable dummy.

gcc/testsuite/ChangeLog:

	PR fortran/109500
	* gfortran.dg/allocatable_function_11.f90: New test.

Co-authored-by: Steven G. Kargl <kargl@gcc.gnu.org>

2 files changed, 48 insertions, 0 deletions

diff --git a/gcc/fortran/interface.cc b/gcc/fortran/interface.cc
index e9843e9..968ee19 100644
--- a/gcc/fortran/interface.cc
+++ b/gcc/fortran/interface.cc
@@ -3638,6 +3638,18 @@ gfc_compare_actual_formal (gfc_actual_arglist **ap, gfc_formal_arglist *formal,
 	  goto match;
 	}
 
+      if (a->expr->expr_type == EXPR_FUNCTION
+	  && a->expr->value.function.esym
+	  && f->sym->attr.allocatable)
+	{
+	  if (where)
+	    gfc_error ("Actual argument for %qs at %L is a function result "
+		       "and the dummy argument is ALLOCATABLE",
+		       f->sym->name, &a->expr->where);
+	  ok = false;
+	  goto match;
+	}
+
       /* Check intent = OUT/INOUT for definable actual argument.  */
       if (!in_statement_function
 	  && (f->sym->attr.intent == INTENT_OUT
diff --git a/gcc/testsuite/gfortran.dg/allocatable_function_11.f90 b/gcc/testsuite/gfortran.dg/allocatable_function_11.f90
new file mode 100644
index 0000000..1a2831e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/allocatable_function_11.f90
@@ -0,0 +1,36 @@
+! { dg-do compile }
+! PR fortran/109500 - check F2018:8.5.3 Note 1
+!
+! The result of referencing a function whose result variable has the
+! ALLOCATABLE attribute is a value that does not itself have the
+! ALLOCATABLE attribute.
+
+program main
+  implicit none
+  integer, allocatable  :: p
+  procedure(f), pointer :: pp
+  pp => f
+  p = f()
+  print *, allocated (p)
+  print *, is_allocated (p)
+  print *, is_allocated (f())  ! { dg-error "is a function result" }
+  print *, is_allocated (pp()) ! { dg-error "is a function result" }
+  call s (p)
+  call s (f())  ! { dg-error "is a function result" }
+  call s (pp()) ! { dg-error "is a function result" }
+
+contains
+  subroutine s(p)
+    integer, allocatable :: p
+  end subroutine s
+
+  function f()
+    integer, allocatable :: f
+    allocate (f, source=42)
+  end function
+
+  logical function is_allocated(p)
+    integer, allocatable :: p
+    is_allocated = allocated(p)
+  end function
+end program