Can initialization of static constant be skipped by 'case' label?

I have a constant declared in one case of my switch statement:

void foo( int& v ) {
    switch( v ) {
    case 0:
        static constexpr int c{ 0 };
        break; 
    case 1:
        v = c;
        break;
    }
}

Everything works fine in GCC, Clang and EDG. But if I compile the program in Visual Studio, it complains

error C2360: initialization of 'c' is skipped by 'case' label

Online demo: https://gcc.godbolt.org/z/jTdnhfzoo

Is it correct that initialization of the constant c can be skipped? Is the program really ill formed or it must be accepted?

Can initialization of static constant be skipped by case label?

No, not if it's constant initialized as in your function.

C++14 6.7.4

Constant initialization ([basic.start.init]) of a block-scope entity with static storage duration, if applicable, is performed before its block is first entered.

This means that your function is valid and will initialize c when the switch block is first entered. A similarly valid function:

void foo(int& v) {
    goto bar;
    static constexpr int c{123};
bar:
    v = c; // assigns 123 to v
}

Removing constexpr doesn't matter here. It'll still be constant initialization of a block-scope entity with static storage duration and therefore performed when the block is first entered.

This bug in MSVC is reported here.

Note: Just because it's valid, it doesn't mean it's a good idea. Don't do this.