[PATCH] D133659: [Clang] P1169R4: static operator()

[Roy Jacobson via Phabricator via cfe-commits]

royjacobson added inline comments.


================
Comment at: clang/include/clang/Basic/DiagnosticParseKinds.td:1037-1041
+def err_static_mutable_lambda : Error<
+  "lambda cannot be both mutable and static">;
+def err_static_lambda_captures : Error<
+  "a static lambda cannot have any captures">;
+def note_lambda_captures : Note<"captures declared here">;
----------------
aaron.ballman wrote:
> These are semantic errors, not parsing ones. This means these will be diagnosed when parsing the lambda rather than when instantiating it. I don't think that matters for the cast of combining `mutable` and `static`, but I'm less certain about "have any captures" because of cases like:
> ```
> template <typename... Types>
> auto func(Types... Ts) {
>   return [Ts...] { return 1; };
> }
> 
> int main() {
>   auto lambda = func();
> }
> ```
> I'm pretty sure that lambda has no captures for that call, but it could have captures depending on the instantiation.
> 
> Actually, from some off-list discussion with @erichkeane, even mutable and static are a problem in code like:
> ```
> template <typename Ty>
> void func(T t) {
>   if constexpr (Something<T>) {
>     [](){};
>   } else {
>     [t](){};
>   }
> ```
> where the lambda is in a discarded statement.
> 
> So I think these might need to change to be Sema diagnostics (and we should add some additional test coverage).
>From https://eel.is/c++draft/expr.prim.lambda.general#4 

> If the lambda-specifier-seq contains static, there shall be no lambda-capture

So this should be a parsing error. Or maybe I don't understand what you're saying. There are no static lambdas in your examples so I'm not sure how they're related.



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