[cfe-dev] C++11 attributes parsing

[Alexander Kornienko]

Once again with updates from Chandler:
At the moment we have several major requirements for c++11 attribute
parsing:
1. all boring attribute subject checks should be automated (using either
TableGen or a static code if this is possible);
2. automated argument parsing (Sean Hunt planned to do this);
3. custom attributes can be added by plugins (Joshua Cranmer has a patch);
4. late parsing for attribute arguments (Chandler: "the thread safety
attributes at the least would benefit from this, and there is definitely a
desire to migrate those to C++11 syntax on our end");
5. automated pretty-printing.

Did I forget anything?

On Mon, Jul 9, 2012 at 1:43 PM, Alexander Kornienko <alexfh at google.com>wrote:

> To summarize, at the moment we have several major requirements for c++11
> attribute parsing:
> 1. all boring attribute subject checks should be automated (using either
> TableGen or a static code if this is possible);
> 2. automated argument parsing (Sean Hunt planned to do this);
> 3. custom attributes can be added by plugins (Joshua Cranmer has a patch);
> 4. late parsing for attribute arguments? (currently no evidence that this
> will be necessary, this would be definitely required, if we decide to add
> c++11 syntax for gcc-style attributes);
> 5. automated pretty-printing.
>
> Did I forget anything?
>
>
On Mon, Jul 9, 2012 at 2:14 PM, Chandler Carruth <chandlerc at google.com>
 wrote:

> On Fri, Jul 6, 2012 at 10:29 AM, John McCall <rjmccall at apple.com> wrote:
>
>> On Jul 6, 2012, at 7:16 AM, Alexander Kornienko wrote:
>> > The whole purpose of this e-mail is to gather ideas regarding our needs
>> for C++11 attributes parsing. Right now, only select attributes are parsed
>> in C++11 style, attribute arguments parsing is not implemented, there's no
>> common check for matching attribute targets ("Subjects" field in Attr.td).
>> BTW, AFAIK, the latter is not implemented for GNU-style attributes either.
>> >
>> > Currently, I see the following questions:
>> > 1. will we allow c++11 syntax for existing GNU attributes?
>>
>> Probably not.  If we do, there's a potential for collision with
>> attributes introduced by the committee.  It doesn't seem to have any
>> benefits except giving users a prettier syntax for writing code that is
>> totally unportable between compilers.
>>
>
> I think there are a very few specific GNU attributes that we should
> support in either syntax: ones that are really Clang attributes but happen
> to be in GNU syntax currently:
>
> - Thread safety attributes
> - Some of the LLVM attributes such as readnone
> - Attributes with very active users that would specifically benefit from
> the improved syntax of C++11 attributes: format string, non-null, and other
> argument-related attributes which are of particular use to static analysis
> tools built in and around clang.
>
> That said, I don't think even these would ever be directly ported. We
> would naturally use the new name spacing utility to pave the way for
> increased portability. I would also assume this would be used as a good
> opportunity to re-think any syntactical problems we've hit over the years,
> and maybe talk to GCC folks to come up with an agreed-upon set of common
> names for those likely to be supported in both compilers (format string,
> non-null, etc).
>
>
>>
>> > 2. what new attributes do we expect to appear in c++11 syntax?
>>
>> Impossible to say;  it depends on the committee.
>>
>> > 3. will they require late parsing of parameters?
>>
>> Unlikely, but possible.
>>
>
> The thread safety attributes at the least would benefit from this, and
> there is definitely a desire to migrate those to C++11 syntax on our end.
>


-- 
Regards,
Alexander
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