Re: [PATCH BZ#19239] Improve deprecation warnings

[Zack Weinberg <zackw at panix dot com>]

On Thu, Oct 13, 2016 at 5:40 PM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
> On 11/10/2016 10:09, Zack Weinberg wrote:
>> By using __glibc_macro_warning instead of __attribute_deprecated__,
>> we get the deprecation warnings whenever the macros are expanded, not
>> just when they compile to a function call.  This is important for
>> unintentional uses like the test case in #19239.
>
> I am assuming you tested some platform and verified that it actually
> fixed the issue.  Patch looks ok with some comments about the new
> macro definition.

Yes, I ran the test suite on x86_64-linux and I manually verified the
test case in #19329.

>> +/* Caution: if you change the whitespace in and around this macro,
>> +   it may malfunction.  Newline placement is tuned for GCC 6.  */
>
> This comments is somewhat confusing, what does it mean to be 'tuned'
> for GCC 6? It is just that stylist it will be better formatted on
> GCC 6? Will it work correctly on older GCC releases? What kind of
> whitespaces constraints do we need to be aware of?

It will work correctly with any GCC release (that supports #pragma GCC
message), it just might not be word-wrapped as neatly.

After thinking about it some more, the fragility is not about
whitespace, it's about tokens.  I have changed the comment to read

/* Caution: The text of this deprecation message is unquoted, so that
   #symbol can be substituted.  (It is converted to a string by
   __SYSMACROS_DM1.)  This means the message must be a sequence of
   complete pp-tokens; in particular, English contractions (it's,
   can't) cannot be used.

   The message has been manually word-wrapped to fit in 80 columns
   when output by GCC 5 and 6.  The first line is shorter to leave
   some room for the "foo.c:23: warning:" annotation.  */

and I've also added a note to cdefs.h above the definition of
__glibc_macro_warning

/* __glibc_macro_warning (MESSAGE) issues warning MESSAGE.  This is
   intended for use in preprocessor macros.

   Note: MESSAGE must be a _single_ string; concatenation of string
   literals is not supported.  */

and I'm going to go ahead and check it in like that.

zw