Re: [PATCH 2/3] meson: detect broken iconv that requires ICONV_RESTART_RESET

> In d0cec08d70 (utf8.c: prepare workaround for iconv under macOS 14/15,
> 2026-01-12) we have introduced a new workaround for a broken version of
> libiconv on macOS. This workaround has for now only been wired up for
> our Makefile, so using Meson with such a broken version will fail.
> 
> We can rather easily detect the broken behaviour. Some encodings have
> different modes that can be switched to via an escape sequence. In the
> case of ISO-2022-JP this can be done via "<Esc>$B" and "<Esc>(J" to
> switch between ASCII and JIS modes. The bug now triggers when one does
> multiple calls to iconv(3p) to convert a string piece by piece, where
> the first call enters JIS mode. The second call forgets about the fact
> that it is still in JIS mode, and consequently it will incorrectly treat
> the input as ASCII, and thus the produced output is of course garbage.
> 
> Wire up a test that exercises this in Meson and, if it fails, set the
> `ICONV_RESTART_RESET` define.

> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  meson.build | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index ee3d9ced92..1b9be3d36c 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1060,6 +1060,32 @@ if iconv.found()
>      ).returncode() != 0
>        libgit_c_args += '-DICONV_OMITS_BOM'
>      endif
> +
> +    if compiler.run('''
> +      #include <iconv.h>
> +      #include <string.h>
> +
> +      int main(int argc, const char *argv[])
> +      {
> +          char in[] = "\x1b\x24\x42\x24\x22\x24\x22\x1b\x28\x42", *inpos = in;

> +          char out[7] = { 0 }, *outpos = out;
> +          size_t insz = sizeof(in) - 1, outsz = 4;
> +          iconv_t conv = iconv_open("UTF-8", "ISO-2022-JP");
> +          if (!conv)
> +              return 1;
> +          if (iconv(conv, (void *) &inpos, &insz, &outpos, &outsz) != (size_t) -1)
> +              return 2;
> +          outsz = sizeof(out) - (outpos - out);
> +          if (iconv(conv, (void *) &inpos, &insz, &outpos, &outsz) == (size_t) -1)
> +              return 3;

> +      }
> +    ''',
> +      dependencies: iconv,
> +      name: 'iconv handles restarts properly',
> +    ).returncode() != 0

> +      libgit_c_args += '-DICONV_RESTART_RESET'
> +    endif
>    endif
>  else
>    libgit_c_args += '-DNO_ICONV'