fix issue 17791 - add __traits(deprecated, symbol)

[dunkyp]

No description provided.

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Bugzilla references

Auto-close	Bugzilla	Description
✓	17791	Add __traits(isDeprecated, ...)

[MartinNowak]

Would it make sense to somehow make the deprecation message introspectable too?

[PetarKirov]

We also need a way to obtain any compiler messages/errors, so I would prefer to leave this PR as it is and focus on a more general solution, like something along the lines of:

struct S
{
    auto opDispatch(string member, T...)(T args)
    {
        static if (args.length % 42 < 13)
            static assert (0, "Solve the mystery!");

        //...
    }
}

enum string[] messages = __traits(captureStdErrOutput,
{
    S s;
    s.theAnswer(1, 2);
});

static assert (messages.canFind("Solve the mystery!"));

[wilzbach]

This should have been accompanied

• by a PR to dlang.org spec (https://dlang.org/spec/traits.html) (at least as long until we don't automatically generate it, see e.g. [Proof of concept] Generate spec from the compiler dlang.org#1688)
• by a changelog entry (https://github.com/dlang/dmd/tree/master/changelog)

@dunkyp would you be so kind to submit the spec & changelog PR? Thanks!

[wilzbach]

Btw has anyone considered the possibility to add this to the existing getFunctionAttributes trait?
After all, there's also no way to check for @future atm.

[PetarKirov]

I also considered getFunctionAttributes, but the deprecated attribute can be applied to more kinds of symbols than just functions. If the trait was called getAttributes or something like that, then yes it would have been a better place add this functionality.