(use-modules (gnu packages pretty-print)
             (gnu packages pkg-config)
             (guix packages)
             (guix gexp)
             (guix transformations)
             (guix build-system meson)
             ((guix licenses) #:select (gpl3+))
             ((guix git-download) #:select (git-file-name))
             (srfi srfi-26))

(define why-hello
  (package
   (name "why-hello")
   (version "0")
   (source (file-union (git-file-name name version)
            `(("hello.cpp" ,(plain-file "hello.cpp"
                       "\
#include <fmt/format.h>

int
main()
{
  fmt::print (\"{}\\n\", \"Hello, world\");
  return 0;
}
"))
              ("meson.build" ,(plain-file "meson.build"
                                          "\
project('hello', 'cpp', default_options: ['cpp_std=c++20'])
executable('hello', files('hello.cpp'), install: true,
           dependencies: [dependency('fmt')])
")))))
   (build-system meson-build-system)
   (inputs (list fmt))
   (native-inputs (list pkg-config))
   (home-page (and=> (current-filename)
                     (cute string-append "file://" <>)))
   (synopsis "Hello world")
   (description "This package provides a simple program that builds with
GCC/G++ normally, but fails miserably when the clang-toolchain is used.")
   (license gpl3+)))

(define why-hello-clang
  ((options->transformation
    '((with-c-toolchain . "why-hello=clang-toolchain")))
   why-hello))

why-hello-clang