Failure building fortran-sdl2 binding interfaces

[angelog0]

flang fails to build fortran-sdl2. For example, as STC

$ flang `sdl2-config --cflags` -O3 -fPIC -c src/c_util.f90
error: Semantic errors in src/c_util.f90
./src/c_util.f90:12:27: error: PARAMETER attribute was already specified on 'c_uint8_t'
      integer, parameter :: c_uint8_t            = c_int8_t
                            ^^^^^^^^^
./src/c_util.f90:12:27: error: 'c_uint8_t' is use-associated from module 'iso_c_binding' and cannot be re-declared
      integer, parameter :: c_uint8_t            = c_int8_t
                            ^^^^^^^^^
[...]

The same command works with gfortran, indeed I use it for my programs!

I tested this in MSYS2/UCRT64 with

$ flang --version
flang version 21.1.1
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/ucrt64/bin

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Angelo Graziosi (angelog0)

`flang` fails to build [fortran-sdl2](https://github.com/interkosmos/fortran-sdl2). For example, as STC

$ flang `sdl2-config --cflags` -O3 -fPIC -c src/c_util.f90
error: Semantic errors in src/c_util.f90
./src/c_util.f90:12:27: error: PARAMETER attribute was already specified on 'c_uint8_t'
      integer, parameter :: c_uint8_t            = c_int8_t
                            ^^^^^^^^^
./src/c_util.f90:12:27: error: 'c_uint8_t' is use-associated from module 'iso_c_binding' and cannot be re-declared
      integer, parameter :: c_uint8_t            = c_int8_t
                            ^^^^^^^^^
[...]

The same command works with gfortran, indeed I use it for my programs!

I tested this in MSYS2/UCRT64 with

$ flang --version
flang version 21.1.1
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:/msys64/ucrt64/bin

[foxtran]

I would recommend to use use, intrinsic :: iso_c_binding, only: for avoiding loading of unsigned types from modern iso_c_binding modules here: https://github.com/interkosmos/fortran-sdl2/blob/c46f9ac46fc0bd834ea8bdac63df33bf8e727f66/src/c_util.f90#L9

However, -fno-unsigned flag does not restrict loading of unsigned types from iso_c_binding and it can be a problem.

[angelog0]

@foxtran wrote

I would recommend to use use, intrinsic :: iso_c_binding, only:

I doubt the author of fortran-sdl2 would change that. In any case, it works with

$ gfortran --version
GNU Fortran (Rev8, Built by MSYS2 project) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[foxtran]

With gfortran it also does not work if one uses -funsigned

https://godbolt.org/z/fs3rxfh6W

[angelog0]

Ok, applying this patch it builds with flang:

$ diff -Naur src/c_util.f90~ src/c_util.f90
--- src/c_util.f90~     2025-09-21 17:09:15.730119100 +0200
+++ src/c_util.f90      2025-09-21 22:29:08.599670200 +0200
@@ -6,7 +6,9 @@
 ! GitHub:  https://github.com/interkosmos/fortran-sdl2/
 ! Licence: ISC
 module c_util
-    use, intrinsic :: iso_c_binding
+  use, intrinsic :: iso_c_binding, only: c_int8_t, c_int16_t, c_int32_t, &
+       c_int64_t, c_int, c_signed_char, c_long, c_long_long, c_short, &
+       c_ptr, c_size_t
     implicit none

     integer, parameter :: c_uint8_t            = c_int8_t

but there are other files as c_utils.f90 :-(

[klausler]

Fortran compilers can add names to the intrinsic modules besides those defined in the standards; see F'2023 16.10.1 p3 "A processor may extend the standard intrinsic modules to provide public entities in them in addition to those specified in this document." It's analogous to compilers being free to add intrinsic procedures.

[akuhlens]

I love the kindness of strangers!

interkosmos/fortran-sdl2@f248b9a

@foxtran do these latest updates help you?

[foxtran]

@foxtran do these latest updates help you?

Better to ask @angelog0 :-)

In my opinion, the patch is a bit dangerous since it introduces C preprocessor and loads everything from iso_c_binding

[akuhlens]

Better to ask @angelog0 :-)

Whoops, I got confused about who filed this issue. @angelog0 Does this help you?

[angelog0]

I get a lot of troubles. It segment faults see the attachments.

flang_files.tar.gz

flang_output.gz

[angelog0]

Also gfortran has some issue