faisalv added a comment.
In https://reviews.llvm.org/D28510#653794, @rsmith wrote:
> I don't think it's possible to check this in the way you're doing so here. In
> general, there's no way to know whether a constant expression will be part of
> a `typedef` declaration or function declaration until you've finished parsing
> it (when you're parsing the decl-specifiers in a declaration you don't know
> whether you're declaring a function or a variable, and the `typedef` keyword
> might appear later).
I see. The issue is that the current approach would forbid valid variable
declarations such as:
void (*f)(int [([]{return 5;}())]) = 0;
... where lambdas can appear within the array declarators (I believe that's the
only syntactic neighborhood that can cause this problem, right?).
> So I think you need a different approach here. How about tracking the set of
> contained lambdas on the `Declarator` and `DeclSpec` objects, and diagnose
> from `ActOnFunctionDeclarator` / `ActOnTypedefDeclarator` if the current
> expression evaluation context contains any lambdas? (Maybe when entering an
> expression evaluation context, pass an optional `SmallVectorImpl<Expr*>*` to
> `Sema` to collect the lambdas contained within the expression.)
Yes - I can see something along these lines working well...
> There are some particularly "fun" cases to watch out for here:
>
> decltype([]{})
> a, // ok
> f(); // ill-formed
>
>
> ... that require us to track the lambdas in the `DeclSpec` separately from
> the lambdas in the `Declarator`.
Well lambda's can't appear in unevaluated operands yet, so your example would
be ill-formed? If so, we don't have to worry about them showing up in
decl-specifiers?
The only Declarator where they could be well formed is within an array
declarator of a variable or a parameter of a function pointer variable (but no
where else, i.e typedefs and function declarations), right?
Thanks!
Repository:
rL LLVM
https://reviews.llvm.org/D28510
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