Allow passing in a top-level env, a map from name to value, to
evaluation. The intent is to support bound identifiers in the REPL just
like upstream nix does.
Getting this working involves mucking around a bit with internals - most
notably, locals now only optionally have a Span (since locals don't have
an easy span we can use) - and getting that working requires propagating
some minor hacks to places where we currently *need* a span (and which
would require too much changing now to make spans optional; my guess is
that that would essentially end up making spans optional throughout the
codebase).
Also, some extra care has to be taken to close out the scope in the case
that we do pass in an env, to avoid breaking our assumptions about the
size of the stack when we return from the toplevel
Change-Id: Ie475b2d3dfc72ccbf298d2a3ea28c63ac877d653
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11953
Tested-by: BuildkiteCI
Autosubmit: aspen <root@gws.fyi>
Reviewed-by: flokli <flokli@flokli.de>
ac3d717944