clang: C++1y deprecated attribute message

[Aaron Ballman]

On Wed, Jan 29, 2014 at 2:04 PM, Richard Smith <metafoo at gmail.com> wrote:
> On Wed Jan 29 2014 at 10:35:46 AM, Aaron Ballman <aaron at aaronballman.com>
> wrote:
>>
>> On Wed, Jan 29, 2014 at 1:07 PM, Richard Smith <metafoo at gmail.com> wrote:
>> > On Wed Jan 29 2014 at 5:36:44 AM, Aaron Ballman <aaron at aaronballman.com>
>> > wrote:
>> >>
>> >> On Wed, Jan 29, 2014 at 2:39 AM, Alp Toker <alp at nuanti.com> wrote:
>> >> >
>> >> > On 29/01/2014 06:30, Richard Smith wrote:
>> >> >
>> >> > On Tue, Jan 28, 2014 at 4:58 PM, Joseph Mansfield
>> >> > <sftrabbit at gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> The attached patch adds support for deprecation messages in C++1y.
>> >> >> This
>> >> >> is
>> >> >> my first time hacking with clang so a code review would definitely
>> >> >> be
>> >> >> needed.
>> >> >>
>> >> >> As an example of what is now supported:
>> >> >>
>> >> >> [[deprecated("use bar instead")]] void foo();
>> >> >>
>> >> >> When this function is used, the following warning is emitted:
>> >> >>
>> >> >> warning: 'foo' is deprecated: use bar instead
>> >> >> [-Wdeprecated-declarations]
>> >> >>   foo();
>> >> >>   ^
>> >> >>
>> >> >> Some tests included.
>> >> >>
>> >> >> Known potential issues:
>> >> >> - Attribute parsing currently doesn't seem to distinguish between
>> >> >> C++11
>> >> >> and C++1y attributes.
>> >> >> - Maybe errors like [[deprecated("foo", "bar")]] would better report
>> >> >> "too
>> >> >> many arguments" than "expected ')'". Not sure about the best way to
>> >> >> go
>> >> >> about
>> >> >> this.
>> >> >
>> >> >
>> >> > Thanks for the patch! The code generally looks good from a style
>> >> > perspective, but please start variable names with a capital letter in
>> >> > new
>> >> > code (the current codebase is woefully inconsistent, but we're trying
>> >> > to
>> >> > get
>> >> > new code to follow the style guide). (The style guide also says to
>> >> > start
>> >> > functions with a lowercase letter, but we're not doing that for
>> >> > Parse*
>> >> > because it's such a well-established pattern that the inconsistency
>> >> > would be
>> >> > worse than following the style guide. We'll get around to doing a
>> >> > mass
>> >> > cleanup of this stuff one day...)
>> >> >
>> >> > We've been trying to move away from having a collection of different
>> >> > attribute argument parsing functions, and towards generating the
>> >> > parsing
>> >> > logic from the Attr.td file -- I'll let Aaron weigh in on whether we
>> >> > want
>> >> > something like ParseAttributeWithMessageArg or whether we should
>> >> > generalize
>> >> > and reuse ParseGNUAttributeArgs.
>> >> >
>> >> >
>> >> > Indeed, this should work already if you remove the check (ScopeName
>> >> > &&
>> >> > ScopeName->getName() == "gnu"):
>> >>
>> >> Alp hit the nail on the head -- the parsing is already handled for the
>> >> GNU case, we can simply reuse it.
>> >
>> >
>> > Alp's suggestion needs some refinement -- the standard attributes (other
>> > than 'deprecated') can't take arguments at all (not even empty
>> > parentheses),
>> > so we'll presumably need some way to encode that in the .td file if we
>> > want
>> > to move away from the hardcoded list.
>>
>> Ah, so this is a parsing issue as well then.
>>
>> Perhaps we could use another meta-spelling: StdCXX that expands to:
>> CXX11<"", name> and CXX11<"std", name>?
>>
>> >>
>> >> I'm not certain we need the IsBuiltInOrStandardCXX11Attribute function
>> >> any longer -- I think this should be declarative-based and handled as
>> >> part of sema, not parsing (in terms of complaining about repeated
>> >> attributes) since it really depends on the attribute, not the
>> >> spelling. Not that it would block this patch.
>> >>
>> >> The new spelling does not appear in Attr.td, which is the only thing I
>> >> really see missing.
>> >
>> >
>> > It's already there and working -- this patch is only adding support for
>> > doing something with the attribute's argument.
>>
>> It has no std scope spelling, which I presume is problematic?
>
>
> I don't see any point in the 'std' attribute namespace, and looking through
> svn history, I can't see any justification being provided when it was added.
> Just remove those spellings entirely?

I see nothing in the standard which suggests these should be in the
std:: namespace, so I'm in favor of removing those spellings.

Then again, I also don't see anything in the standard claiming that
unscoped attributes are reserved which makes me fearful for naming
collisions with different semantics between implementations. :-(

~Aaron