Normalize "empty" string values to a canonical form for comparison in the config watcher

Author: EhabY

src/configWatcher.ts

@@ -26,14 +26,28 @@ export function watchConfigurationChanges(
 
 			const newValue = getValue();
 
-			if (!isDeepStrictEqual(newValue, appliedValues.get(setting))) {
+			if (!configValuesEqual(newValue, appliedValues.get(setting))) {
 				changedSettings.push(setting);
-				appliedValues.set(setting, newValue);
 			}
+			appliedValues.set(setting, newValue);
 		}
 
 		if (changedSettings.length > 0) {
 			onChange(changedSettings);
 		}
 	});
 }
+
+function configValuesEqual(a: unknown, b: unknown): boolean {
+	return isDeepStrictEqual(normalizeEmptyValue(a), normalizeEmptyValue(b));
+}
+
+/**
+ * Normalize "empty" string values to a canonical form for comparison.
+ */
+function normalizeEmptyValue(value: unknown): unknown {
+	if (value === undefined || value === null || value === "") {
+		return undefined;
+	}
+	return value;
+}

test/unit/configWatcher.test.ts

@@ -94,4 +94,43 @@ describe("watchConfigurationChanges", () => {
 		expect(changes).toEqual([["test.setting"]]);
 		dispose();
 	});
+
+	it("treats undefined, null, and empty string as equivalent", () => {
+		const config = new MockConfigurationProvider();
+		config.set("test.setting", undefined);
+		const { changes, dispose } = createWatcher("test.setting");
+
+		config.set("test.setting", null);
+		config.set("test.setting", "");
+		config.set("test.setting", undefined);
+
+		expect(changes).toEqual([]);
+		dispose();
+	});
+
+	interface ValueChangeTestCase {
+		name: string;
+		from: unknown;
+		to: unknown;
+	}
+
+	it.each<ValueChangeTestCase>([
+		{ name: "undefined to value", from: undefined, to: "value" },
+		{ name: "value to empty string", from: "value", to: "" },
+		{ name: "undefined to false", from: undefined, to: false },
+		{ name: "undefined to zero", from: undefined, to: 0 },
+		{ name: "undefined to empty array", from: undefined, to: [] },
+		{ name: "null to value", from: null, to: "value" },
+		{ name: "empty string to value", from: "", to: "value" },
+		{ name: "value to different value", from: "old", to: "new" },
+	])("detects change: $name", ({ from, to }) => {
+		const config = new MockConfigurationProvider();
+		config.set("test.setting", from);
+		const { changes, dispose } = createWatcher("test.setting");
+
+		config.set("test.setting", to);
+
+		expect(changes).toEqual([["test.setting"]]);
+		dispose();
+	});
 });