refactor(core): Add warning when signal equality is false for object.is (#52532)

atscott · atscott · commit f887792c8378 · 2023-11-06T15:53:09.000-08:00
This commit adds a warning when a signal equality function returns `false` but `Object.is` returns `true`. PR Close #52532
diff --git a/packages/core/primitives/signals/src/signal.ts b/packages/core/primitives/signals/src/signal.ts
@@ -10,6 +10,10 @@ import {defaultEquals, ValueEqualityFn} from './equality';
 import {throwInvalidWriteToSignalError} from './errors';
 import {producerAccessed, producerIncrementEpoch, producerNotifyConsumers, producerUpdatesAllowed, REACTIVE_NODE, ReactiveNode, SIGNAL} from './graph';
 
+// Required as the signals library is in a separate package, so we need to explicitly ensure the
+// global `ngDevMode` type is defined.
+declare const ngDevMode: boolean|undefined;
+
 /**
  * If set, called after `WritableSignal`s are updated.
  *
@@ -63,9 +67,13 @@ export function signalSetFn<T>(node: SignalNode<T>, newValue: T) {
   }
 
   const value = node.value;
-  // assuming that signal value equality implementations should always return true for values that
-  // are the same according to Object.is
-  if (!Object.is(value, newValue) && !node.equal(value, newValue)) {
+  if (Object.is(value, newValue)) {
+    if (typeof ngDevMode !== 'undefined' && ngDevMode && !node.equal(value, newValue)) {
+      console.warn(
+          'Signal value equality implementations should always return `true` for' +
+          ' values that are the same according to `Object.is` but returned `false` instead.');
+    }
+  } else if (!node.equal(value, newValue)) {
     node.value = newValue;
     signalValueChanged(node);
   }
