This PR refines and clarifies the `meta` phase distinction in the module
system.
* `meta import A` without `public` now has the clarified meaning of
"enable compile-time evaluation of declarations in or above `A` in the
current module, but not downstream". This is now checked statically by
enforcing that public meta defs, which therefore may be referenced from
outside, can only use public meta imports, and that global evaluating
attributes such as `@[term_parser]` can only be applied to public meta
defs.
* `meta def`s may no longer reference non-meta defs even when in the
same module. This clarifies the meta distinction as well as improves
locality of (new) error messages.
* parser references in `syntax` are now also properly tracked as meta
references.
* A `meta import` of an `import` now properly loads only the `.ir` of
the nested module for the purposes of execution instead of also making
its declarations available for general elaboration.
* `initialize` is now no longer being run on import under the module
system, which is now covered by `meta initialize`.
This command comes from Lean 3, which I had previously ported and
contributed to Batteries (née Std). In this new version, `#where`
produces actual command Syntax for all features of a top-level scope
(rather than splicing together strings), and it also now reports
included variables.
---------
Co-authored-by: Kim Morrison <kim@tqft.net>
