From 19836e29f23a70223e3e5601b33345b9bdf617aa Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 17 Apr 2025 08:16:27 -0400
Subject: [PATCH] chore: add log_effect_tree utility (#15780)

---
 .../svelte/src/internal/client/dev/debug.js   | 109 ++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 packages/svelte/src/internal/client/dev/debug.js

diff --git a/packages/svelte/src/internal/client/dev/debug.js b/packages/svelte/src/internal/client/dev/debug.js
new file mode 100644
index 0000000000..f449dfa2cc
--- /dev/null
+++ b/packages/svelte/src/internal/client/dev/debug.js
@@ -0,0 +1,109 @@
+/** @import { Derived, Effect, Value } from '#client' */
+
+import {
+	BLOCK_EFFECT,
+	BOUNDARY_EFFECT,
+	BRANCH_EFFECT,
+	CLEAN,
+	DERIVED,
+	EFFECT,
+	MAYBE_DIRTY,
+	RENDER_EFFECT,
+	ROOT_EFFECT
+} from '../constants.js';
+
+/**
+ *
+ * @param {Effect} effect
+ */
+export function root(effect) {
+	while (effect.parent !== null) {
+		effect = effect.parent;
+	}
+
+	return effect;
+}
+
+/**
+ *
+ * @param {Effect} effect
+ */
+export function log_effect_tree(effect, depth = 0) {
+	const flags = effect.f;
+
+	let label = '(unknown)';
+
+	if ((flags & ROOT_EFFECT) !== 0) {
+		label = 'root';
+	} else if ((flags & BOUNDARY_EFFECT) !== 0) {
+		label = 'boundary';
+	} else if ((flags & BLOCK_EFFECT) !== 0) {
+		label = 'block';
+	} else if ((flags & BRANCH_EFFECT) !== 0) {
+		label = 'branch';
+	} else if ((flags & RENDER_EFFECT) !== 0) {
+		label = 'render effect';
+	} else if ((flags & EFFECT) !== 0) {
+		label = 'effect';
+	}
+
+	let status =
+		(flags & CLEAN) !== 0 ? 'clean' : (flags & MAYBE_DIRTY) !== 0 ? 'maybe dirty' : 'dirty';
+
+	// eslint-disable-next-line no-console
+	console.group(`%c${label} (${status})`, `font-weight: ${status === 'clean' ? 'normal' : 'bold'}`);
+
+	if (depth === 0) {
+		const callsite = new Error().stack
+			?.split('\n')[2]
+			.replace(/\s+at (?: \w+\(?)?(.+)\)?/, (m, $1) => $1.replace(/\?[^:]+/, ''));
+
+		// eslint-disable-next-line no-console
+		console.log(callsite);
+	}
+
+	if (effect.deps !== null) {
+		// eslint-disable-next-line no-console
+		console.groupCollapsed('%cdeps', 'font-weight: normal');
+
+		for (const dep of effect.deps) {
+			log_dep(dep);
+		}
+
+		// eslint-disable-next-line no-console
+		console.groupEnd();
+	}
+
+	let child = effect.first;
+	while (child !== null) {
+		log_effect_tree(child, depth + 1);
+		child = child.next;
+	}
+
+	// eslint-disable-next-line no-console
+	console.groupEnd();
+}
+
+/**
+ *
+ * @param {Value} dep
+ */
+function log_dep(dep) {
+	if ((dep.f & DERIVED) !== 0) {
+		const derived = /** @type {Derived} */ (dep);
+
+		// eslint-disable-next-line no-console
+		console.groupCollapsed('%cderived', 'font-weight: normal', derived.v);
+		if (derived.deps) {
+			for (const d of derived.deps) {
+				log_dep(d);
+			}
+		}
+
+		// eslint-disable-next-line no-console
+		console.groupEnd();
+	} else {
+		// eslint-disable-next-line no-console
+		console.log('state', dep.v);
+	}
+}