More robust vdbg! macro (vercel/turborepo#4995)

### Description

I ran into a couple of issues with the vdbg! macro:
* The macro tries to move its parameters within an async block, which
requires everything that's moved to be both `Copy` and `'static` to work
properly. This would break when trying to pass `&obj.property`, where
the reference doesn't have a `'static` lifetime. Instead, I'm adding the
requirement on parameters to impl `ToOwned` so we can ensure the
`'static` lifetime, and creating an owned version of the parameter to
move into the future.
* The `CELL_COUNTERS` thread local could be unset when calling
`.value_debug_format().try_to_string()`, which would panic the thread.

crates/turbo-tasks/src/debug/vdbg.rs

@@ -16,22 +16,34 @@ macro_rules! vdbg {
         eprintln!("[{}:{}]", file!(), line!())
     };
 
-    (__init $depth:expr ; $($val:expr),* ) => {
+    (__init $depth:expr ; [ $val:expr $(, $rest:expr)* ] [ $($tt:tt)* ] ) => {
+        {
+            let valstr = stringify!($val);
+            // We move the value into a new binding so we may refer to it multiple
+            // times without re-evaluating the expression.
+            let valmove = $val;
+            // We convert the value to an owned value which will be moved into the
+            // spawned thread. This is necessary in order to ensure a 'static lifetime
+            // for the value, but it may require a clone.
+            let valowned = valmove.to_owned();
+            $crate::vdbg!(__init $depth ; [ $($rest),* ] [ $($tt)* valstr valmove valowned ])
+        }
+    };
+    (__init $depth:expr ; [ ] [ $($valstr:ident $valmove:ident $valowned:ident)* ] ) => {
         {
             use $crate::debug::ValueDebugFormat;
             let depth = $depth;
             $crate::macro_helpers::spawn_detached(async move {
-                $crate::vdbg!(__expand depth ; [ $($val),* ] []);
+                $crate::vdbg!(__expand depth ; [ $($valstr $valowned)* ] []);
                 Ok(())
             });
-            ($($val),*)
+            ($($valmove),*)
         }
     };
 
-    (__expand $depth:ident ; [ $val:expr $(, $rest:expr )* ] [ $($tt:tt)* ]) => {
-        let valstr = stringify!($val);
+    (__expand $depth:ident ; [ $valstr:ident $val:ident $($rest:tt)* ] [ $($tt:tt)* ]) => {
         let valdbg = (&$val).value_debug_format($depth).try_to_string().await?;
-        $crate::vdbg!(__expand $depth ; [ $($rest),* ] [ $($tt)* valstr valdbg ]);
+        $crate::vdbg!(__expand $depth ; [ $($rest)* ] [ $($tt)* $valstr valdbg ]);
     };
     (__expand $depth:ident ; [] [ $( $valstr:ident $valdbg:ident )* ]) => {
         // By pre-awaiting, then printing everything at once, we ensure that the
@@ -57,6 +69,6 @@ macro_rules! vdbg {
         $crate::vdbg!(__init $depth ; $($val),*)
     };
     ($($val:expr),+ $(,)?) => {
-        $crate::vdbg!(__init usize::MAX ; $($val),*)
+        $crate::vdbg!(__init usize::MAX ; [ $($val),* ] [])
     };
 }

crates/turbo-tasks/src/manager.rs

@@ -995,7 +995,10 @@ impl<B: Backend + 'static> TurboTasksApi for TurboTasks<B> {
             turbo_tasks(),
             CURRENT_TASK_ID.scope(
                 current_task_id,
-                self.backend.execution_scope(current_task_id, f),
+                CELL_COUNTERS.scope(
+                    Default::default(),
+                    self.backend.execution_scope(current_task_id, f),
+                ),
             ),
         ))
     }