feat(tvix/eval): Implement builtins.tryEval

With asserts compiled using conditional jumps, this ends up being quite
straightforward - the only real tricky bit is that we have to know
whether an error can or can't be handled.

Change-Id: I75617da73b7a9c5cdd888c0e26ae81d2c5c0d714
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6924
Reviewed-by: sterni <sternenseemann@systemli.org>
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

tvix/eval/src/errors.rs

@@ -158,6 +158,17 @@ impl From<io::Error> for ErrorKind {
     }
 }
 
+impl ErrorKind {
+    /// Returns `true` if this error can be caught by `builtins.tryEval`
+    pub fn is_catchable(&self) -> bool {
+        match self {
+            Self::Throw(_) | Self::AssertionFailed => true,
+            Self::ThunkForce(err) => err.kind.is_catchable(),
+            _ => false,
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct Error {
     pub kind: ErrorKind,