[SOLVED] `noexcept(noexcept(expr))` on lambda in MSVC

`noexcept(noexcept(expr))` on lambda in MSVC

I'm seeing a compile error in MSVC with this:

constexpr auto f = 
    [](auto&& x, auto&&... someOtherStuff) noexcept(noexcept(x)) {};

which gives me

<source>(3): error C2760: syntax error: 'someOtherStuff' was unexpected here; expected ')'

And as I changed things around, this shouldn't compile but I get an internal compiler error:

constexpr auto g = 
    [](auto&&... someOtherStuff) noexcept(noexcept(int)) {}; //< ICE

https://godbolt.org/z/faKKfjdPx

Is f, above, correct C++? It (and the ICE) goes away with /std:c++20 or with other compilers.

Solution

Yes, f is correct, but g is not:

noexcept operator:

Syntax

noexcept( expression )

int is not an expression, but the compiler should of course not ICE.

Without compiling with /permissive- in pre C++20, MSVC follows its own rules (often in conflict with standard C++ rules) and doesn't compile f. If you do add /permissive- or upgrade to C++20 (which sets /permissive- by default), the error goes away.