[PATCH] Fortran: reject NULL actual argument without explicit interface [PR107576]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

one cannot pass a NULL actual argument to a procedure without an
explicit interface.  This is detected and reported by NAG and Intel.
(Cray accepts this silently, and some other brands ICE.)

The testcase by Gerhard even tricked gfortran into inconsistent
behavior which could lead to an ICE with -fallow-argument-mismatch,
or silently accepting invalid code.

The solution is to reject such code, see attached patch.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

As this is marked as a regression which started at v7,
OK for backports to open branches?

Thanks,
Harald


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From c6b19d662f51b1e2d2691e81cfeb68ad953a4c09 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Thu, 17 Nov 2022 21:36:49 +0100
Subject: [PATCH] Fortran: reject NULL actual argument without explicit
 interface [PR107576]

gcc/fortran/ChangeLog:

	PR fortran/107576
	* interface.cc (gfc_procedure_use): Reject NULL as actual argument
	when there is no explicit procedure interface.

gcc/testsuite/ChangeLog:

	PR fortran/107576
	* gfortran.dg/null_actual_3.f90: New test.
---
 gcc/fortran/interface.cc                    |  8 ++++++++
 gcc/testsuite/gfortran.dg/null_actual_3.f90 | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 gcc/testsuite/gfortran.dg/null_actual_3.f90

diff --git a/gcc/fortran/interface.cc b/gcc/fortran/interface.cc
index 616ae2b1197..73799c175b7 100644
--- a/gcc/fortran/interface.cc
+++ b/gcc/fortran/interface.cc
@@ -4162,6 +4162,14 @@ gfc_procedure_use (gfc_symbol *sym, gfc_actual_arglist **ap, locus *where)
 	      return false;
 	    }

+	  if (a->expr && a->expr->expr_type == EXPR_NULL)
+	    {
+	      gfc_error ("Passing intrinsic NULL as actual argument at %L "
+			 "requires an explicit interface", &a->expr->where);
+	      a->expr->error = 1;
+	      return false;
+	    }
+
 	  /* TS 29113, C407b.  */
 	  if (a->expr && a->expr->expr_type == EXPR_VARIABLE
 	      && symbol_rank (a->expr->symtree->n.sym) == -1)
diff --git a/gcc/testsuite/gfortran.dg/null_actual_3.f90 b/gcc/testsuite/gfortran.dg/null_actual_3.f90
new file mode 100644
index 00000000000..ea49f9630c9
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/null_actual_3.f90
@@ -0,0 +1,18 @@
+! { dg-do compile }
+! { dg-options "-fallow-argument-mismatch -w" }
+! PR fortran/107576
+! Contributed by G.Steinmetz
+
+program p
+  implicit none
+  interface
+     subroutine r(y)
+       integer, pointer :: y(:)
+     end subroutine r
+  end interface
+  integer, pointer :: z(:) => null()
+  call r(z)
+  call s(z)
+  call r(null(z))
+  call s(null(z)) ! { dg-error "requires an explicit interface" }
+end
--
2.35.3