runtime, vm: write thunk results back to the forcing stack slot

fix-vm/src/instructions/calls.rs

@@ -34,6 +34,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(Continuation::CallPattern.ip() as usize);
             return Step::Continue(());
@@ -47,6 +48,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
             pc: resume_pc,
             thunk: None,
             env: m.env(),
+            depth: None,
         });
         reader.set_pc(ip as usize);
         m.set_env(new_env);
@@ -57,6 +59,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(primop.dispatch_ip as usize)
         } else {
@@ -77,6 +80,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
                 pc: resume_pc,
                 thunk: None,
                 env: m.env(),
+                depth: None,
             });
             reader.set_pc(app.primop.dispatch_ip as usize)
         } else {
@@ -101,6 +105,7 @@ pub(crate) fn call<'gc, M: Machine<'gc>>(
             pc: resume_pc,
             thunk: None,
             env: m.env(),
+            depth: None,
         });
         m.push(arg);
         m.push(func.relax());
@@ -140,6 +145,7 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
         pc: ret_pc,
         thunk,
         env,
+        depth,
     }) = m.pop_call_frame()
     else {
         match m.force_mode() {
@@ -156,6 +162,7 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
                     pc: Continuation::ForceResultDeepFinish.ip() as usize,
                     thunk: None,
                     env: m.env(),
+                    depth: None,
                 });
                 m.inc_call_depth();
                 reader.set_pc(Continuation::PDeepSeq.ip() as usize);
@@ -166,6 +173,9 @@ pub(crate) fn op_return<'gc, M: Machine<'gc>>(
     reader.set_pc(ret_pc);
     if let Some(outer_thunk) = thunk {
         *outer_thunk.borrow_mut(mc) = ThunkState::Evaluated(val);
+        if let Some(depth) = depth {
+            m.replace(depth, val.relax());
+        }
     } else {
         m.dec_call_depth();
         m.push(val.relax())

fix-vm/src/instructions/with_scope.rs

@@ -41,6 +41,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
                         thunk: Some(thunk),
                         pc: resume_pc,
                         env: m.env(),
+                        depth: None,
                     });
                     m.set_env(env);
                     reader.set_pc(ip);
@@ -52,6 +53,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
                         thunk: Some(thunk),
                         pc: resume_pc,
                         env: m.env(),
+                        depth: None,
                     });
                     m.push(func);
                     return m.call(reader, mc, arg, resume_pc);

fix-vm/src/lib.rs

@@ -211,6 +211,7 @@ impl<'gc> Machine<'gc> for Vm<'gc> {
                     thunk: Some(thunk),
                     pc: resume_pc,
                     env: self.env,
+                    depth: Some(depth),
                 });
                 self.env = env;
                 reader.set_pc(ip);
@@ -225,6 +226,7 @@ impl<'gc> Machine<'gc> for Vm<'gc> {
                     thunk: Some(thunk),
                     pc: resume_pc,
                     env: self.env,
+                    depth: Some(depth),
                 });
                 self.push(func);
                 self.call(reader, mc, arg, resume_pc)

fix-vm/src/primops/eq.rs

@@ -166,6 +166,7 @@ fn enter_eq_machine<'gc, M: Machine<'gc>>(
         pc: resume_pc,
         thunk: None,
         env: m.env(),
+        depth: None,
     });
     m.inc_call_depth();
     m.push(Value::new(negate));

fix-vm/src/primops/io.rs

@@ -46,6 +46,7 @@ pub fn import<'gc, M: Machine<'gc>>(
         pc: Continuation::PImportFinalize.ip() as usize,
         thunk: None,
         env,
+        depth: None,
     });
 
     m.set_pending_load(PendingLoad {
@@ -79,6 +80,7 @@ pub fn import_finalize<'gc, M: Machine<'gc>>(
         pc: ret_pc,
         thunk: _,
         env,
+        depth: None,
     }) = m.pop_call_frame()
     else {
         unreachable!()
@@ -120,6 +122,7 @@ pub fn scoped_import<'gc, M: Machine<'gc>>(
         pc: Continuation::PScopedImportFinalize.ip() as usize,
         thunk: None,
         env,
+        depth: None,
     });
 
     m.set_pending_load(PendingLoad {