chore(build/compiler): Enable a bunch of strict TS compiler options. (#6138)

packages/cli/src/utils/checks.ts

@@ -0,0 +1,28 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Fail to compile on unexpected values. */
+export function assumeExhaustive(_value: never): void {}
+
+/**
+ * Throws an exception on unexpected values.
+ *
+ * A common use case is switch statements:
+ * switch(enumValue) {
+ *   case Enum.A:
+ *   case Enum.B:
+ *     break;
+ *   default:
+ *     checkExhaustive(enumValue);
+ * }
+ */
+export function checkExhaustive(
+  value: never,
+  msg = `unexpected value ${value}!`,
+): never {
+  assumeExhaustive(value);
+  throw new Error(msg);
+}