Dear all,
due to an oversight in the Fortran standard before 2018,
empty derived types with bind(C) attribute were explicitly
(deliberately?) accepted by gfortran, giving a warning that
the companion processor might not provide an interoperating
entity.
In the PR, Tobias pointed to a discussion on the J3 ML that
there was a defect in older standards. The attached patch
now generates an error when -std=f20xx is specified, and
continues to generate a warning otherwise.
Regtested on x86_64-pc-linux-gnu. OK for mainline?
Thanks,
Harald
From 5c38ce50ed7cca905401f6fa6506b47fd79a7739 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anl...@gmx.de>
Date: Sun, 2 Mar 2025 22:20:28 +0100
Subject: [PATCH] Fortran: reject empty derived type with bind(C) attribute
[PR101577]
PR fortran/101577
gcc/fortran/ChangeLog:
* symbol.cc (verify_bind_c_derived_type): Generate error message
for derived type with no components in standard conformance mode,
indicating that this is a GNU extension.
gcc/testsuite/ChangeLog:
* gfortran.dg/empty_derived_type.f90: Adjust dg-options.
* gfortran.dg/empty_derived_type_2.f90: New test.
---
gcc/fortran/symbol.cc | 22 ++++++++++++++++---
.../gfortran.dg/empty_derived_type.f90 | 1 +
.../gfortran.dg/empty_derived_type_2.f90 | 11 ++++++++++
3 files changed, 31 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gfortran.dg/empty_derived_type_2.f90
diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
index c6894810bce..9ddf13b3f0d 100644
--- a/gcc/fortran/symbol.cc
+++ b/gcc/fortran/symbol.cc
@@ -4624,12 +4624,28 @@ verify_bind_c_derived_type (gfc_symbol *derived_sym)
entity may be defined by means of C and the Fortran entity is said
to be interoperable with the C entity. There does not have to be such
an interoperating C entity."
+
+ However, later discussion on the J3 mailing list
+ (https://mailman.j3-fortran.org/pipermail/j3/2021-July/013190.html)
+ found this to be a defect, and Fortran 2018 added in section 18.3.4
+ the following constraint:
+ "C1805: A derived type with the BIND attribute shall have at least one
+ component."
+
+ We thus allow empty derived types only as GNU extension while giving a
+ warning by default, or reject empty types in standard conformance mode.
*/
if (curr_comp == NULL)
{
- gfc_warning (0, "Derived type %qs with BIND(C) attribute at %L is empty, "
- "and may be inaccessible by the C companion processor",
- derived_sym->name, &(derived_sym->declared_at));
+ if (!gfc_notify_std (GFC_STD_GNU, "Derived type %qs with BIND(C) "
+ "attribute at %L has no components",
+ derived_sym->name, &(derived_sym->declared_at)))
+ return false;
+ else if (!pedantic)
+ gfc_warning (0, "Derived type %qs with BIND(C) attribute at %L "
+ "is empty, and may be inaccessible by the C "
+ "companion processor",
+ derived_sym->name, &(derived_sym->declared_at));
derived_sym->ts.is_c_interop = 1;
derived_sym->attr.is_bind_c = 1;
return true;
diff --git a/gcc/testsuite/gfortran.dg/empty_derived_type.f90 b/gcc/testsuite/gfortran.dg/empty_derived_type.f90
index 6bf616c2c6a..496262de2cd 100644
--- a/gcc/testsuite/gfortran.dg/empty_derived_type.f90
+++ b/gcc/testsuite/gfortran.dg/empty_derived_type.f90
@@ -1,4 +1,5 @@
! { dg-do compile }
+! { dg-options "" }
module stuff
implicit none
type, bind(C) :: junk ! { dg-warning "may be inaccessible by the C companion" }
diff --git a/gcc/testsuite/gfortran.dg/empty_derived_type_2.f90 b/gcc/testsuite/gfortran.dg/empty_derived_type_2.f90
new file mode 100644
index 00000000000..1ef56da4c25
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/empty_derived_type_2.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+! { dg-additional-options "-std=f2018" }
+!
+! PR fortran/101577
+!
+! Contributed by Tobias Burnus
+
+type, bind(C) :: t ! { dg-error "has no components" }
+ ! Empty!
+end type t
+end
--
2.43.0
