Templates: two-phase name lookup

[isnullxbh]

Live example: https://godbolt.org/z/TqM35b
Env.: macOS 10.15.7,  ICC 2021.1 Beta 20201112

The following example compiles without error, but the internalCheck function doesn't depend on one of the template parameters, so we should get a compile-time error (according to the https://eel.is/c++draft/temp.res#general-10)

template<typename Context,
         typename Protocol>
auto createSocket(Context& context, const Protocol& protocol) -> auto
{
    using Socket = typename Protocol::Socket;
    internalCheck();
    return Socket { context, protocol };
}

[RahulV_intel]

Hi,

Thanks for reporting this bug. I have escalated this to the concerned team for a fix.

Regards,

Rahul

[Viet_H_Intel]

Thank you for reporting this issue. I've filed a bug with our compiler Developer.

[Viet_H_Intel · Accepted solution]

Our Developer said: "This is not really a bug; but perhaps a compatibility/usability issue (Microsoft doesn't emit error)"

The C++ standard does not require a compiler to give diagnostics on a template that has not been used/instantiated.

From the standard: This is a quality of implementation issue, it is ill-formed but if it is not instantiated no diagnostic is required as per [temp.res#8.1]p:

The validity of a template may be checked prior to any instantiation. [ Note: Knowing which names are type names allows the syntax of every template to be checked in this way. — end note ] The program is ill-formed, no diagnostic required, if:

no valid specialization can be generated for a template or a substatement of a constexpr if statement within a template and the template is not instantiated.

Thanks,

[isnullxbh]

@Viet_H_Intel, thanks for the explanations!

[Viet_H_Intel]

We are closing the thread as the issue has been resolved and we will no longer respond to this thread. If you require additional assistance from Intel, please start a new thread. Any further interaction in this thread will be considered community only.

Thanks,