[Issue 21725] New: Specifying null as bitfields variable name now fails

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21725

          Issue ID: 21725
           Summary: Specifying null as bitfields variable name now fails
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: dlang-bugzilla at thecybershadow.net

//////// test.d ////////
import std.bitmanip;

struct S
{
    mixin(bitfields!(
        uint, q{foo}, 4,
        uint, null, 4,
    ));
}
////////////////////////

As of 2.096, fails with:

.../src/phobos/std/bitmanip.d(300): Error: static assert:  "Variable name
expected, found null"

Introduced in https://github.com/dlang/phobos/pull/7793

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