feat(tvix/eval): initial implementation of `builtins.import` r/5041

This adds an initial working version of builtins.import which
encapsulates the entire functionality of `import` within the builtin
itself, without requiring any changes in the compiler or VM.

The key insight that enables this is that we can simply return a Thunk
from `import` that is constructed from the output of running the
compiler and - ta-da! - no other component needs to know about it.

A couple of notes:

* builtins.import needs to capture variables like the SourceCode
  structure. This means it can not currently be constructed the same
  way as other builtins and has special handling, which leaks out to
  `eval.rs`. I have postponed dealing with that until we have this
  working a bit more.

* the `globals` are not yet passed through

* the error representation for the new variants is absolutely not done
  yet, we probably want to switch to something that supports
  cause-chaining now (like miette)

* there is no mechanism for emitting warnings at runtime; we need to
  add that

Change-Id: I3117a7ae3ff2432bf44f5ff05ad35f47faca31d5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6857
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

1 files changed, 1 insertions, 1 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index ad3ab807e3..b0aab352d2 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -19,7 +19,7 @@ use crate::{arithmetic_op, cmp_op};
 use self::versions::{VersionPart, VersionPartsIter};
 
 #[cfg(feature = "impure")]
-mod impure;
+pub mod impure;
 pub mod versions;
 
 /// Coerce a Nix Value to a plain path, e.g. in order to access the file it