chore: remove deopts and refactor code for controlled optimizations (#11040)

* chore: remove deopts and refactor code for controlled optimizations

* remove comment

* tune

* tweak

* tweak

* typo

* get rid of single-use variable

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

packages/svelte/src/internal/client/dom/blocks/each.js

@@ -17,8 +17,10 @@ import {
 	branch,
 	effect,
 	pause_effect,
+	get_out_transitions,
+	resume_effect,
 	pause_effects,
-	resume_effect
+	destroy_effects
 } from '../../reactivity/effects.js';
 import { source, mutable_source, set } from '../../reactivity/sources.js';
 import { is_array, is_frozen, map_get, map_set } from '../../utils.js';
@@ -244,9 +246,17 @@ function reconcile_indexed_array(array, state, anchor, render_fn, flags) {
 			effects.push(a_items[i].e);
 		}
 
-		pause_effects(effects, () => {
-			state.items.length = b;
-		});
+		var transitions = get_out_transitions(effects);
+		var items = state.items;
+
+		if (transitions.length === 0) {
+			destroy_effects(effects);
+			items.length = b;
+		} else {
+			pause_effects(effects, transitions, () => {
+				items.length = b;
+			});
+		}
 	}
 }
 
@@ -421,11 +431,16 @@ function reconcile_tracked_array(array, state, anchor, render_fn, flags, keys) {
 		});
 	}
 
-	// TODO: would be good to avoid this closure in the case where we have no
-	// transitions at all. It would make it far more JIT friendly in the hot cases.
-	pause_effects(to_destroy, () => {
+	var transitions = get_out_transitions(to_destroy);
+
+	if (transitions.length === 0) {
+		destroy_effects(to_destroy);
 		state.items = b_items;
-	});
+	} else {
+		pause_effects(to_destroy, transitions, () => {
+			state.items = b_items;
+		});
+	}
 }
 
 /**

packages/svelte/src/internal/client/reactivity/effects.js

@@ -313,23 +313,38 @@ export function pause_effect(effect, callback = noop) {
  * Pause multiple effects simultaneously, and coordinate their
  * subsequent destruction. Used in each blocks
  * @param {import('#client').Effect[]} effects
- * @param {() => void} callback
+ * @returns {import('#client').TransitionManager[]}
  */
-export function pause_effects(effects, callback = noop) {
+export function get_out_transitions(effects) {
 	/** @type {import('#client').TransitionManager[]} */
 	var transitions = [];
-	var length = effects.length;
 
-	for (var i = 0; i < length; i++) {
+	for (var i = 0; i < effects.length; i++) {
 		pause_children(effects[i], transitions, true);
 	}
 
-	// TODO: would be good to avoid this closure in the case where we have no
-	// transitions at all. It would make it far more JIT friendly in the hot cases.
+	return transitions;
+}
+
+/**
+ * @param {import('#client').Effect[]} effects
+ */
+export function destroy_effects(effects) {
+	for (var i = 0; i < effects.length; i++) {
+		destroy_effect(effects[i]);
+	}
+}
+
+/**
+ * Pause multiple effects simultaneously, and coordinate their
+ * subsequent destruction. Used in each blocks
+ * @param {import('#client').Effect[]} effects
+ * @param {import('#client').TransitionManager[]} transitions
+ * @param {() => void} callback
+ */
+export function pause_effects(effects, transitions, callback = noop) {
 	out(transitions, () => {
-		for (var i = 0; i < length; i++) {
-			destroy_effect(effects[i]);
-		}
+		destroy_effects(effects);
 		callback();
 	});
 }
@@ -370,13 +385,12 @@ function pause_children(effect, transitions, local) {
 	var child = effect.first;
 
 	while (child !== null) {
-		var sibling = child.next;
 		var transparent = (child.f & IS_ELSEIF) !== 0 || (child.f & BRANCH_EFFECT) !== 0;
 		// TODO we don't need to call pause_children recursively with a linked list in place
 		// it's slightly more involved though as we have to account for `transparent` changing
 		// through the tree.
 		pause_children(child, transitions, transparent ? local : false);
-		child = sibling;
+		child = child.next;
 	}
 }