refactor(tvix/eval): encapsulate all thunk-forcing logic in module r/4700

The VM previously took care of repeatedly forcing a thunk until it
reached an evaluated state. This logic is now encapsulated inside of
the `Thunk::force` implementation.

In addition, force no longer returns a reference to the value by
default, leaving it up to callers to decide whether they want to
borrow the value or not (a helper is provided for this).

Change-Id: I2aa7da922058ad1c57fbf8bfc7785aab7971c02b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6365
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index c55bc81777f1..d85f31a3cb02 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -444,8 +444,9 @@ impl VM {
                 OpCode::OpForce => {
                     let mut value = self.pop();
 
-                    while let Value::Thunk(thunk) = value {
-                        value = thunk.force(self)?.clone();
+                    if let Value::Thunk(thunk) = value {
+                        thunk.force(self)?;
+                        value = thunk.value().clone();
                     }
 
                     self.push(value);