fix(tvix/eval): do not fail when finalising non-capturing values r/5020

This can actually legitimately be emitted by the compiler currently
when compiling formals with default values. See the scope6 test from
the Nix test suite for an example.

We should restructure this slightly to be able to reintroduce a
runtime error here in case something was compiled incorrectly.

Change-Id: Ib81f0f58ae0e850db9fbc459458b7bd0d3ac6f23
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6841
Autosubmit: tazjin <tazjin@tvl.su>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

1 files changed, 6 insertions, 1 deletions

diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 72d672688217..39c9c6e822df 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -589,7 +589,12 @@ impl<'o> VM<'o> {
                         Value::Thunk(thunk) => thunk
                             .resolve_deferred_upvalues(&self.stack[self.frame().stack_offset..]),
 
-                        v => panic!("compiler error: invalid finaliser value: {}", v),
+                        // In functions with "formals" attributes, it is
+                        // possible for `OpFinalise` to be called on a
+                        // non-capturing value, in which case it is a no-op.
+                        //
+                        // TODO: detect this in some phase and skip the finalise; fail here
+                        _ => { /* TODO: panic here again to catch bugs */ }
                     }
                 }