[Issue 24857] New: Unknown error while instantiating: __traits(compiles) hides the real issue

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24857

          Issue ID: 24857
           Summary: Unknown error while instantiating: __traits(compiles)
                    hides the real issue
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ilya.yanok at gmail.com

dustmite minimized example (probably could be minimized a bit further):
```
template AllMembersInModule(alias Module) {
    import std: AliasSeq, Filter;
    alias all_members = AliasSeq!(__traits(allMembers, Module));

    template CanAccess(string member) {
        enum CanAccess = __traits(compiles, __traits(getMember, Module,
member));
    }
    alias x = Filter!(CanAccess, all_members);

    alias AllMembersInModule = y;
}

template t() {
    alias MODULE = __traits(parent, {});
    static foreach (M; AllMembersInModule!MODULE) {
        }
}

alias AllMembers = AllMembersInModule!(__traits(parent, {}));
mixin t;
```

The issue here is a typo: `y` should be `x`, but we get an unknown error
instead.

If I remove `alias AllMembers` it works as expected.

BTW, if I remove `mixin t` line, it compiles without error, is it expected, are
aliases lazy?

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