Remove some slightly overengineered stuff

crates/egui_kittest/src/lib.rs

@@ -87,8 +87,6 @@ pub struct Harness<'a, State: 'static = ()> {
     queued_events: EventQueue,
 
     plugins: Vec<Box<dyn Plugin<State>>>,
-    pending_plugins: Vec<Box<dyn Plugin<State>>>,
-    in_dispatch: bool,
     entry_location: Option<&'static std::panic::Location<'static>>,
     consumed_event_locations: Vec<&'static std::panic::Location<'static>>,
     last_accesskit_update: Option<egui::accesskit::TreeUpdate>,
@@ -181,8 +179,6 @@ impl<'a, State: 'static> Harness<'a, State> {
             queued_events: Default::default(),
 
             plugins,
-            pending_plugins: Vec::new(),
-            in_dispatch: false,
             entry_location: None,
             consumed_event_locations: Vec::new(),
             last_accesskit_update: Some(initial_accesskit),
@@ -206,13 +202,12 @@ impl<'a, State: 'static> Harness<'a, State> {
     /// Register a [`Plugin`] after construction.
     ///
     /// See [`HarnessBuilder::with_plugin`] to register before the first frame runs.
+    ///
+    /// Calling this from inside a plugin hook is allowed — the new plugin is appended to
+    /// the list but does not receive the currently-dispatching hook; it starts firing on
+    /// the next dispatch.
     pub fn add_plugin(&mut self, plugin: impl Plugin<State>) {
-        let boxed: Box<dyn Plugin<State>> = Box::new(plugin);
+        self.plugins.push(Box::new(plugin));
-        if self.in_dispatch {
-            self.pending_plugins.push(boxed);
-        } else {
-            self.plugins.push(boxed);
-        }
     }
 
     /// Borrow a registered plugin by type. Returns the first plugin of the matching type
@@ -246,11 +241,9 @@ impl<'a, State: 'static> Harness<'a, State> {
 
     /// Advance the harness by one frame without firing plugin hooks.
     ///
-    /// Use this from inside a plugin hook when the plugin needs to drive additional
+    /// This is useful for running steps within a plugin, without ending in an infinite loop where
-    /// frames — e.g. an inspector plugin that blocks on user input and re-renders
+    /// the plugin is called again.
-    /// after each injected event. Calling [`Self::step`] or [`Self::run`] from inside
+    pub fn step_no_side_effects(&mut self) {
-    /// a hook would recurse infinitely through that plugin's own `after_step`.
-    pub fn advance_frame(&mut self) {
         self._step_inner(false);
     }
 
@@ -276,17 +269,13 @@ impl<'a, State: 'static> Harness<'a, State> {
             return;
         }
         let mut plugins = std::mem::take(&mut self.plugins);
-        self.in_dispatch = true;
         for p in &mut plugins {
             f(p.as_mut(), self);
         }
-        self.in_dispatch = false;
+        // Handle the case where a plugin is registered within some other plugin
+        let added = std::mem::take(&mut self.plugins);
         self.plugins = plugins;
-        // Promote any plugins registered mid-dispatch to the end of the active list.
+        self.plugins.extend(added);
-        if !self.pending_plugins.is_empty() {
-            let pending = std::mem::take(&mut self.pending_plugins);
-            self.plugins.extend(pending);
-        }
     }
 
     /// Create a new Harness with the given ui closure and a state.
@@ -346,10 +335,6 @@ impl<'a, State: 'static> Harness<'a, State> {
     /// update the Harness.
     #[track_caller]
     pub fn step(&mut self) {
-        debug_assert!(
-            !self.in_dispatch,
-            "Harness::step called from inside a plugin hook — use Harness::advance_frame instead to avoid infinite recursion"
-        );
         self.entry_location = Some(std::panic::Location::caller());
         let events = std::mem::take(&mut *self.queued_events.lock());
         if events.is_empty() {
@@ -381,7 +366,7 @@ impl<'a, State: 'static> Harness<'a, State> {
     }
 
     /// Core frame advance. Does NOT fire plugin hooks — callable from within
-    /// hooks via [`Self::advance_frame`] without recursing.
+    /// hooks via [`Self::step_no_side_effects`] without recursing.
     fn _step_inner(&mut self, sizing_pass: bool) {
         self.input.predicted_dt = self.step_dt;
 
@@ -465,10 +450,6 @@ impl<'a, State: 'static> Harness<'a, State> {
     }
 
     fn _try_run(&mut self, sleep: bool) -> Result<u64, ExceededMaxStepsError> {
-        debug_assert!(
-            !self.in_dispatch,
-            "Harness::run / Harness::try_run called from inside a plugin hook — use Harness::advance_frame instead to avoid infinite recursion"
-        );
         self.dispatch(|p, h| p.before_run(h));
 
         let mut steps = 0;

crates/egui_kittest/src/plugin.rs

@@ -34,10 +34,9 @@ use crate::{ExceededMaxStepsError, Harness};
 /// # Re-entrancy
 ///
 /// Plugin hooks receive `&mut Harness`. Calling [`Harness::step`] / [`Harness::run`] /
-/// etc. from inside a hook is forbidden (it would recurse infinitely through your own
+/// etc. from inside a hook will recurse infinitely through your own `after_step`. If
-/// `after_step`) and is caught by a `debug_assert!`. If a plugin needs to advance the
+/// a plugin needs to advance the harness from inside a hook — e.g. an inspector that
-/// harness from inside a hook — e.g. an inspector that blocks on user input — use
+/// blocks on user input — use [`Harness::advance_frame`] instead.
-/// [`Harness::advance_frame`] instead.
 #[expect(unused_variables, reason = "default no-op impls")]
 pub trait Plugin<State = ()>: Send + Any {
     /// Called once at the start of every `run()` / `try_run()` / `try_run_realtime()` /

crates/egui_kittest/tests/plugin.rs

@@ -233,26 +233,6 @@ fn on_test_result_sees_panic() {
     assert_eq!(last, Some("on_test_result:fail"), "log = {log:?}");
 }
 
-/// Calling `Harness::step` from inside a plugin hook should panic in debug builds
-/// (the `in_dispatch` guard).
-#[cfg(debug_assertions)]
-#[test]
-#[should_panic(expected = "inside a plugin hook")]
-fn reentrant_step_panics_in_debug() {
-    struct Misbehaver;
-    impl<S: 'static> Plugin<S> for Misbehaver {
-        fn after_step(&mut self, h: &mut Harness<'_, S>) {
-            // Forbidden: step from inside a hook.
-            h.step();
-        }
-    }
-
-    let mut harness = Harness::builder().with_plugin(Misbehaver).build_ui(|ui| {
-        ui.label("hi");
-    });
-    harness.step();
-}
-
 /// `on_snapshot` fires with an Err result for a missing snapshot.
 #[cfg(feature = "snapshot")]
 #[test]