feat(tvix/eval): implement OpFinalise instruction r/4667

This instruction finalises the initialisation of deferred upvalues in
closures (and soon, thunks).

The compiler does not yet emit this instruction, some more accounting
is needed for that.

Change-Id: Ic4181b26e19779e206f51e17388559400da5f93a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6337
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tvix/eval/src/value/function.rs b/tvix/eval/src/value/function.rs
index e5db43d58a..e8301d82da 100644
--- a/tvix/eval/src/value/function.rs
+++ b/tvix/eval/src/value/function.rs
@@ -60,4 +60,15 @@ impl Closure {
     pub fn push_upvalue(&self, value: Value) {
         self.0.borrow_mut().upvalues.push(value)
     }
+
+    /// Resolve the deferred upvalues in the closure from a slice of
+    /// the current stack, using the indices stored in the deferred
+    /// values.
+    pub fn resolve_deferred_upvalues(&self, stack: &[Value]) {
+        for upvalue in self.0.borrow_mut().upvalues.iter_mut() {
+            if let Value::DeferredUpvalue(idx) = upvalue {
+                *upvalue = stack[idx.0].clone();
+            }
+        }
+    }
 }