[patch/rfc] An opt-in warning for functions whose availability(introduced) is newer than the deployment target

[Nico Weber]

Ping.

Another way to think about this warning is that it effectively ignores
declarations where the introduced version is higher than the deployment
version.

On Thu, Jan 8, 2015 at 6:14 PM, Nico Weber <thakis at chromium.org> wrote:

> Hi,
>
> the Mac OS X and iOS SDKs add new functions in new releases. Apple
> recommends using the newest SDK and setting the deployment target to
> whatever old OS version one wants to support, and only calling new
> functions after checking that they are available at runtime.
>
> In practice, we (Chromium) get this wrong. Others who support old OS X
> versions get this wrong too. Hence, we (Chromium) use a very old SDK and
> then manually declare new functions when we want to call them – this
> reduces the chance of us forgetting if they are available at runtime
> considerably, in practice. But using an old SDK has its problems –
> sometimes the frameworks check which SDK an app was linked against and only
> then activate bug fixes, and newer Xcodes don't ship include old SDKs.
>
> Ideally, we could use a new SDK but get a warning when we use a new API
> without a manual redeclaration – this protects us against new APIs the same
> way using an old SDK does without the drawbacks that this brings.
>
> The attached patch is a sketch how such a warning might work. How
> repulsive is this idea? Are there other approaches to this problem? If the
> basic idea is ok: Any comments on the implementation?
>
> I'm not sure who should look at this. dgregor, you wrote r128127 which
> looks in the same area.
>
> Thanks,
> Nico
>
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