This fix introduces the same encapsulation as the copymap. There is no easy
way of doing this any better for now.
hg up -r null && time HGRCPATH= HGMODULEPOLICY=rust+c hg up tip on Mozilla
Central, (not super recent, but it doesn't matter):
Before: 7:44,08 total
After: 1:03,23 total
Pretty brutal regression!
This is a graft on stable of cf1f8660e568