add simple suspense methods

packages/core/src/scopes.rs

@@ -1,7 +1,6 @@
 use crate::{
     any_props::AnyProps,
     any_props::VProps,
-    arena::ElementId,
     bump_frame::BumpFrame,
     innerlude::{DynamicNode, EventHandler, VComponent, VText},
     innerlude::{ErrorBoundary, Scheduler, SchedulerMsg},
@@ -169,6 +168,7 @@ pub struct ScopeState {
     pub(crate) id: ScopeId,
 
     pub(crate) height: u32,
+    pub(crate) suspended: Cell<bool>,
 
     pub(crate) hooks: RefCell<Vec<Box<UnsafeCell<dyn Any>>>>,
     pub(crate) hook_idx: Cell<usize>,
@@ -182,7 +182,6 @@ pub struct ScopeState {
     pub(crate) attributes_to_drop: RefCell<Vec<*const Attribute<'static>>>,
 
     pub(crate) props: Option<Box<dyn AnyProps<'static>>>,
-    pub(crate) placeholder: Cell<Option<ElementId>>,
 }
 
 impl<'src> ScopeState {
@@ -655,6 +654,12 @@ impl<'src> ScopeState {
         None
     }
 
+    /// Mark this component as suspended and then return None
+    pub fn suspend(&self) -> Option<()> {
+        self.suspended.set(true);
+        None
+    }
+
     /// Store a value between renders. The foundational hook for all other hooks.
     ///
     /// Accepts an `initializer` closure, which is run on the first use of the hook (typically the initial render). The return value of this closure is stored for the lifetime of the component, and a mutable reference to it is provided on every render as the return value of `use_hook`.