refactor(tvix/eval): remove `todo!()` calls in compiler r/4823

It is impossible for tvixbolt to recover from panics, so the user
experience of typing an expression using an unsupported feature was
that it would get sad and stop responding to input.

Instead, raise a normal value-level error of a new variant and
continue where possible.

Change-Id: Ibe016c92cacb87b85095c0f83758eddc6468053e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6528
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index ad4acd479e..b87555d06d 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -58,6 +58,11 @@ pub enum ErrorKind {
     /// An error occured while forcing a thunk, and needs to be
     /// chained up.
     ThunkForce(Box<Error>),
+
+    /// Tvix internal warning for features triggered by users that are
+    /// not actually implemented yet, and without which eval can not
+    /// proceed.
+    NotImplemented(&'static str),
 }
 
 #[derive(Clone, Debug)]