[m-rev.] diff: do not warn about obsolete autoconf macros

[Julien Fischer]

On Mon, 7 Jun 2021, Peter Wang wrote:

> On Mon, 07 Jun 2021 15:43:18 +1000 Julien Fischer <jfischer at opturion.com> wrote:
>>
>> On Mon, 7 Jun 2021, Peter Wang wrote:
>>
>>> On Mon, 07 Jun 2021 15:19:55 +1000 Julien Fischer <jfischer at opturion.com> wrote:
>>>>
>>>> From autoconf 2.70 onwards, obsolescence warnings are enabled by default.
>>>> Recently I have fixed all the warnings we were getting, except for:
>>>>
>>>> 1. With autoconf 2.70 we get a warning about our use of AC_PROG_LEX;
>>>> this cannot be avoided while preserving support for autoconf 2.69
>>>
>>> Can we use AC_PATH_PROG to search for flex instead?
>>
>> The correct fix (as per the comment I added to configure.ac) is to use
>> AC_PROG_LEX([noyywrap]), but that's only supported by 2.70+.
>>
>
> If we don't make use of any of the portability checks done by
> AC_PROG_LEX (and I think we don't) then we should be able to just search
> for flex until we are ready to require autoconf 2.70.
>
> But that's more work, so I don't mind if you just disable the warnings.

Ok.

>>>> 2. Warnings about escaping of quotes and double quotes, like:
>>>>
>>>>      warning: back quotes and double quotes must not be escaped in:
>>>>      $as_me:${as_lineno-$LINENO}: WARNING: cannot find a working \`mkfifo' or \`mknod'
>>>>
>>>> I haven't (yet) found a way to avoid this warning and get a configure
>>>> script that works :-(  Suggestions welcome.
>>>
>>> Does 'single quotes' work?
>>
>> Yes, it works.  Doing that will mean that the configure output will use
>> a different quoting style from configure --help (which is fine by me).
>
> Me too. I'm a little surprised configure is still using `this quoting
> style'.

Given the scarcity of autoconf developers, I suspect it's not a priority
for them.  I'll update configure.ac to use single quotes.

Julien.