Expander not using lexical context of macro definition site

Created by: 97jaz

This:

var umem = new Uint8Array(1024);

macro word {
  rule { ($addr:expr) } => { ((umem[$addr] << 8) | umem[($addr)+1]) }
}

word(4);

expands to this:

var umem$186 = new Uint8Array(1024);
umem[4] << 8 | umem[4 + 1];

So, umem is being renamed at its definition site, but the expansion isn't using that name.