Re: [PATCH v2 4/5] meson: replace Perl usage with Python

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 9 Jan 2023 at 18:16, <marcandre.lureau@redhat.com> wrote:
>
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> Let's try to remove Perl usage during build time.
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  tests/qapi-schema/meson.build | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/tests/qapi-schema/meson.build b/tests/qapi-schema/meson.build
> index 9dfe98bc9a..d85b14f28c 100644
> --- a/tests/qapi-schema/meson.build
> +++ b/tests/qapi-schema/meson.build
> @@ -259,22 +259,23 @@ if build_docs
>    # Fix possible inconsistency in line endings in generated output and
>    # in the golden reference (which could otherwise cause test failures
>    # on Windows hosts). Unfortunately diff --strip-trailing-cr
> -  # is GNU-diff only. The odd-looking perl is because we must avoid
> +  # is GNU-diff only. The odd-looking python is because we must avoid
>    # using an explicit '\' character in the command arguments to
>    # a custom_target(), as Meson will unhelpfully replace it with a '/'
>    # (https://github.com/mesonbuild/meson/issues/1564)

This comment is not applicable to your Python rewrite of this.
It's talking about the way that the Perl code has to create
a variable with a '\r' value in a weird way (using "$x = chr 13")
and then do a substitution using that variable, rather than the obvious
direct s// command ("s/\r//"), to work around a meson bug if the code
has a literal \ character in it. Your python has no '\'s in it.

> +  remove_cr = [python, '-c', 'import sys;[sys.stdout.write(line.replace(chr(13), "")) for line in sys.stdin]']
>    qapi_doc_out_nocr = custom_target('QAPI rST doc newline-sanitized',
>                                      output: ['doc-good.txt.nocr'],
>                                      input: qapi_doc_out[0],
>                                      build_by_default: true,
> -                                    command: ['perl', '-pe', '$x = chr 13; s/$x$//', '@INPUT@'],
> +                                    command: [remove_cr, '@INPUT@'],
>                                      capture: true)
>
>    qapi_doc_ref_nocr = custom_target('QAPI rST doc reference newline-sanitized',
>                                      output: ['doc-good.ref.nocr'],
>                                      input: files('doc-good.txt'),
>                                      build_by_default: true,
> -                                    command: ['perl', '-pe', '$x = chr 13; s/$x$//', '@INPUT@'],
> +                                    command: [remove_cr, '@INPUT@'],
>                                      capture: true)
>
>    test('QAPI rST doc', diff, args: ['-u', qapi_doc_ref_nocr[0], qapi_doc_out_nocr[0]],
> --
> 2.39.0

Maybe we should consider putting the Python into a script in
scripts/ ? "Remove \r characters" is pretty trivial, but on the
other hand I think this is the only Meson custom_target() we
have where we directly invoke a script interpreter with a
bit of inline script, and inline bits of script doesn't really
seem to be a style Meson encourages (unlike Make).

thanks
-- PMM