[Issue 20863] New: Pass into template by alias drops qualifier

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20863

          Issue ID: 20863
           Summary: Pass into template by alias drops qualifier
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: andrei at erdani.com

Took me a while to make this 100% self-contained. Both asserts should pass. The
second fails.

alias AliasSeq(Seq...) = Seq;

template staticIndexOf(alias T, TList...)
{
    static if (TList.length == 0)
    {
        enum int staticIndexOf = -1;
    }
    else static if (is(T == TList[0]))
    {
        enum int staticIndexOf = 0;
    }
    else
    {
        private enum int t = staticIndexOf!(T, TList[1 .. $]);
        enum int staticIndexOf = t < 0 ? t : t + 1;
    }
}

struct Foo {}

static assert(staticIndexOf!(Foo, AliasSeq!(Foo)) == 0); // pass
static assert(staticIndexOf!(immutable(Foo), AliasSeq!(immutable(Foo))) == 0);
// fail

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