handle nightmarish infinite loop situation

src/compile/render-dom/wrappers/Element/index.ts

@@ -757,7 +757,7 @@ export default class ElementWrapper extends Wrapper {
 			block.builders.intro.addConditional(`@intro.enabled`, deindent`
 				if (${name}) ${name}.invalidate();
 
-				@after_update(() => {
+				@after_render(() => {
 					if (!${name}) ${name} = @wrapTransition(#component, ${this.var}, ${fn}, ${snippet}, true);
 					${name}.run(1);
 				});
@@ -792,7 +792,7 @@ export default class ElementWrapper extends Wrapper {
 				}
 
 				block.builders.intro.addConditional(`@intro.enabled`, deindent`
-					@after_update(() => {
+					@after_render(() => {
 						${introName} = @wrapTransition(#component, ${this.var}, ${fn}, ${snippet}, true);
 						${introName}.run(1);
 					});

src/internal/Component.js

@@ -1,4 +1,4 @@
-import { schedule_update, flush, intro } from './scheduler.js';
+import { after_render, flush, intro, schedule_update } from './scheduler.js';
 import { set_current_component } from './lifecycle.js'
 import { is_function, run, run_all, noop } from './utils.js';
 import { blankObject } from './utils.js';
@@ -33,11 +33,13 @@ export class $$Component {
 			this.$$.inject_props(options.props);
 		}
 
+		run_all(this.$$beforeRender);
 		this.$$fragment = this.$$create_fragment(this, this.$$.get_state());
 
 		if (options.target) {
 			intro.enabled = !!options.intro;
 			this.$$mount(options.target);
+
 			flush();
 			intro.enabled = true;
 		}
@@ -90,7 +92,6 @@ export class $$Component {
 	}
 
 	$$mount(target, anchor) {
-		run_all(this.$$beforeRender);
 		this.$$fragment.c();
 		this.$$fragment[this.$$fragment.i ? 'i' : 'm'](target, anchor);
 		this.$$.inject_refs(this.$$refs);
@@ -99,15 +100,16 @@ export class $$Component {
 		this.$$onDestroy.push(...onDestroy);
 		this.$$onMount = [];
 
-		run_all(this.$$afterRender);
+		this.$$afterRender.forEach(after_render);
 	}
 
 	$$update() {
 		run_all(this.$$beforeRender);
 		this.$$fragment.p(this.$$dirty, this.$$.get_state());
 		this.$$.inject_refs(this.$$refs);
-		run_all(this.$$afterRender);
 		this.$$dirty = null;
+
+		this.$$afterRender.forEach(after_render);
 	}
 }
 

src/internal/scheduler.js

@@ -1,7 +1,7 @@
 let update_scheduled = false;
 
-const dirty_components = [];
-const after_update_callbacks = [];
+let dirty_components = [];
+const after_render_callbacks = [];
 
 export const intro = { enabled: false };
 
@@ -13,18 +13,33 @@ export function schedule_update(component) {
 	}
 }
 
-export function after_update(fn) {
-	after_update_callbacks.push(fn);
+export function after_render(fn) {
+	after_render_callbacks.push(fn);
 }
 
 export function flush() {
-	while (dirty_components.length) {
-		dirty_components.pop().$$update();
-	}
-
-	while (after_update_callbacks.length) {
-		after_update_callbacks.shift()();
-	}
+	const seen_callbacks = new Set();
+
+	do {
+		// first, call beforeRender functions
+		// and update components
+		while (dirty_components.length) {
+			dirty_components.shift().$$update();
+		}
+
+		// then, once components are updated, call
+		// afterRender functions. This may cause
+		// subsequent updates...
+		while (after_render_callbacks.length) {
+			const callback = after_render_callbacks.pop();
+			if (!seen_callbacks.has(callback)) {
+				callback();
+
+				// ...so guard against infinite loops
+				seen_callbacks.add(callback);
+			}
+		}
+	} while (dirty_components.length);
 
 	update_scheduled = false;
 }