Re: `btowc' deprecated in Android NDK r30

Hi Po Lu,

> Building Emacs with the latest prerelease of r30 of the Android NDK,
> with an __ANDROID_API__ of 36, yields the following warning in Gnulib:
> ...
> /home/[...]/android-ndk-r30-beta1/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/wchar.h:182:39: note: 'btowc' has been explicitly marked deprecated here
>   182 | wint_t btowc(int __ch) __attribute__((__deprecated__("ASCII-only; use mbtowc() instead")));
>       |                                       ^

This warning is pointless, because btowc is an ISO C function and
therefore will not go away (anytime soon).

I can see the change in the bionic git (
$ git clone https://android.googlesource.com/platform/bionic
$ git checkout android17-release
) in commit b4e215d67df79a79834690d69970807fdfe35173, which has
the title "Document the uselessness of btowc()/wctob()."
So, the intent is just to enhance the documentation of this function,
not to prepare for its removal.

The "deprecation" message "use mbtowc() instead" is nonsense, because
btowc() is thread-safe, while mbtowc() is not.

The same warning could also apply to all <ctype.h> functions. But the
Bionic developer has not changed <ctype.h> accordingly.

> I think some measures should be taken to suppress or address this
> warning.

Not in Gnulib. Just ignore it, like the sprintf() or strcat() warnings
on OpenBSD.

But feel free to report it to Elliott Hughes <[email protected]>, so that
he can provide an opt-out for the warning and fix the message. That's
the point of having prereleases, right?

Bruno