From 4cd8a05180c6f141fd88aa9ef088668e4dc94067 Mon Sep 17 00:00:00 2001
From: Michel Weststrate <mweststrate@gmail.com>
Date: Thu, 1 Sep 2016 23:04:09 +0200
Subject: [PATCH] Added error message when endless recursion is nigh

---
 src/core/computedvalue.ts | 14 +++++++++++---
 test/observables.js       | 16 ++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/core/computedvalue.ts b/src/core/computedvalue.ts
index a32f2b634..4a9e08bb6 100644
--- a/src/core/computedvalue.ts
+++ b/src/core/computedvalue.ts
@@ -46,6 +46,7 @@ export class ComputedValue<T> implements IObservable, IComputedValue<T>, IDeriva
 	protected value: T = undefined;
 	name: string;
 	isComputing: boolean = false; // to check for cycles
+	isRunningSetter: boolean = false; // TODO optimize, see: https://reaktor.com/blog/javascript-performance-fundamentals-make-bluebird-fast/
 	setter: (value: T) => void;
 
 	/**
@@ -129,10 +130,17 @@ export class ComputedValue<T> implements IObservable, IComputedValue<T>, IDeriva
 	}
 
 	public set(value: T) {
-		if (this.setter)
-			this.setter.call(this.scope, value);
+		if (this.setter) {
+			invariant(!this.isRunningSetter, `The setter of computed value '${this.name}' is trying to update itself. Did you intend to update an _observable_ value, instead of the computed property?`);
+			this.isRunningSetter = true;
+			try {
+				this.setter.call(this.scope, value);
+			} finally {
+				this.isRunningSetter = false;
+			}
+		}
 		else
-			throw new Error(`[ComputedValue '${this.name}'] It is not possible to assign a new value to a computed value.`);
+			invariant(false, `[ComputedValue '${this.name}'] It is not possible to assign a new value to a computed value.`);
 	}
 
 	private trackAndCompute(): boolean {
diff --git a/test/observables.js b/test/observables.js
index 2aa5d43fd..65fad621e 100644
--- a/test/observables.js
+++ b/test/observables.js
@@ -1876,3 +1876,19 @@ test('computed getter / setter for plan objects should succeed', function (t) {
 
 	t.end();
 });
+
+test('helpful error for self referencing setter', function(t) {
+	var a = observable({
+		x: 1,
+		get y() {
+			return this.x
+		},
+		set y(v) {
+			this.y = v // woops...;-)
+		}
+	})
+
+	t.throws(() => a.y = 2, /The setter of computed value/)
+
+	t.end()
+})