r245352 - Workaround -Wdeprecated on SemDiagnosticConsumer's tricksy copy ctor.

[Richard Smith via cfe-commits]

On Tue, Aug 18, 2015 at 2:03 PM, David Blaikie <dblaikie at gmail.com> wrote:

> Richard, do you think there's anything we could do better here?
>
> It seems difficult to support proper move semantic behavior for
> [Sema]DiagnosticBuilder across the two common use cases:
>
>   DiagnosticBuilder D;
>   D << x;
>   D << y;
>   return D;
>
> and
>
>   return DiagnosticBuilder() << x << y;
>

Do we actually use this form to return a DiagnosticBuilder, or just to
construct an ActionResult? Can we eliminate uses of this form?


> The only thing I can imagine is if every one of those op<< were function
> templates using universal references (I forget, is that the right name for
> them?) and matching their return value (so in the first case, passed a
> non-const lvalue ref, they return by non-const lvalue ref, and in the
> second case, passed an rvalue, they return the same). But that seems
> painful.
>

It seems tricky to form an unambiguous overload set for this that preserves
the value category, without duplicating all the operator<<s.


> On Tue, Aug 18, 2015 at 1:54 PM, David Blaikie via cfe-commits <
> cfe-commits at lists.llvm.org> wrote:
>
>> Author: dblaikie
>> Date: Tue Aug 18 15:54:26 2015
>> New Revision: 245352
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=245352&view=rev
>> Log:
>> Workaround -Wdeprecated on SemDiagnosticConsumer's tricksy copy ctor.
>>
>> Modified:
>>     cfe/trunk/include/clang/Sema/Sema.h
>>
>> Modified: cfe/trunk/include/clang/Sema/Sema.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=245352&r1=245351&r2=245352&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/include/clang/Sema/Sema.h (original)
>> +++ cfe/trunk/include/clang/Sema/Sema.h Tue Aug 18 15:54:26 2015
>> @@ -1054,6 +1054,14 @@ public:
>>      SemaDiagnosticBuilder(DiagnosticBuilder &DB, Sema &SemaRef, unsigned
>> DiagID)
>>        : DiagnosticBuilder(DB), SemaRef(SemaRef), DiagID(DiagID) { }
>>
>> +    // This is a cunning lie. DiagnosticBuilder actually performs move
>> +    // construction in its copy constructor (but due to varied uses,
>> it's not
>> +    // possible to conveniently express this as actual move
>> construction). So
>> +    // the default copy ctor here is fine, because the base class
>> disables the
>> +    // source anyway, so the user-defined ~SemaDiagnosticBuilder is a
>> safe no-op
>> +    // in that case anwyay.
>> +    SemaDiagnosticBuilder(const SemaDiagnosticBuilder&) = default;
>> +
>>      ~SemaDiagnosticBuilder() {
>>        // If we aren't active, there is nothing to do.
>>        if (!isActive()) return;
>>
>>
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>
>
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