akePureMalloc cannot be interpreted at compile time

[Adnan via Digitalmars-d-learn]

The following program produces an error message and it is not 
clear exactly what line causes this error:

module maybe;
@nogc:
private import std.container : Array;

struct MayBe(T) {
        Array!T data;

        this(T datum) {
                data.reserve(1);
                data.insert(datum);
        }

        T unwrap() const {
                return data[0];
        }

        T unwrapOr(T alternateValue) const {
                return isSome() ? unwrap() : alternateValue;
        }

        bool isSome() const {
                return !data.empty();
        }

        bool isNone() const {
                return !isSome();
        }

        bool contains(T arg) const {
                return isSome() && unwrap() == arg;
        }

        T expect(lazy string msg) const {
                if (isNone()) {
                        import core.stdc.stdio : puts;
                        import core.stdc.stdlib : exit;

                        puts(msg.ptr);
                        exit(-1);
                }
                return unwrap();
        }

        void nullify() {
                data.clear();
        }

        void insert(T datum) {
                if (isNone())
                        data.insert(datum);
                else
                        data.front = datum;
        }
}

MayBe!T flatten(T)(MayBe!(MayBe!T) arg) {
        return isSome() ? arg.unwrap() : some!T();
}

MayBe!T some(T)(T arg) {
        return MayBe!T(arg);
}

MayBe!T none(T)() {
        return MayBe!T();
}

unittest {
        alias MB = MayBe;

        MB!int a;
        assert(a.isNone);

        auto b = none!int();
        assert(b.isNone);

        auto c = some!int(23);
        assert(c.contains(23));

        c.nullify();

        assert(a == c);

        a.insert(11);
        c.insert(11);
        assert(a == c);

        auto d = some!(some!int(9));
        assert(d.flatten() == some!int(9));
}

$ dub test
Generating test runner configuration 'maybe-test-library' for 
'library' (library).
Performing "unittest" build using dmd for x86_64.
maybe ~master: building configuration "maybe-test-library"...
/snap/dmd/99/bin/../import/phobos/std/internal/memory.d(31,33): 
Error: fakePureMalloc cannot be interpreted at compile time, 
because it has no available source code
dmd failed with exit code 1.

And what is the meaning of this error message?