[PATCH] D55662: [Sema][ObjC] Do not warn about repeated uses of weak variables when the variables are accessed in an unevaluated context.

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

In D55662#1335146 <https://reviews.llvm.org/D55662#1335146>, @ahatanak wrote:

> Here are a couple of examples I found running the regression tests:
>
>   int f0(int);
>   float f0(float);
>   decltype(f0) f0_a; // this is not valid.
>
>
>
>
>   template <class... Ts>
>   int var_expr(Ts... ts);
>  
>   template <class... Ts>
>   auto a_function(Ts... ts) -> decltype(var_expr(ts...));
>  
>   template <class T>
>   using partial = decltype(a_function<int, T>);
>  
>   int use_partial() { partial<char> n; }
>
>
>
>
>   template<class T> void oneT() { }
>   int main()
>   {
>     decltype(oneT<int>)* fun = 0;
>   }
>
>
> If the call to `CheckPlaceholderExpr` in `Sema::BuildDecltypeType` is moved to `TreeTransform<Derived>::TransformDecltypeType` and `Parser::ParseDecltypeSpecifier`, we can assert at the beginning of `Sema::BuildDecltypeType`.


Okay, I'm not really understanding what path goes through those two places but not through `ActOnDecltypeExpression`, since both of them seem to unconditionally call the latter (at least, in the expression-parsing path).


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