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

packages/cli/src/ui/commands/directoryCommand.tsx

@@ -138,13 +138,11 @@ export const directoryCommand: SlashCommand = {
 
         if (errors.length > 0) {
           addItem(
-            {
-              type: MessageType.ERROR,
-              text: errors.join('\n'),
-            },
+            { type: MessageType.ERROR, text: errors.join('\n') },
             Date.now(),
           );
         }
+        return;
       },
     },
     {

packages/cli/src/ui/components/shared/vim-buffer-actions.ts

@@ -19,6 +19,7 @@ import {
   findWordEndInLine,
 } from './text-buffer.js';
 import { cpLen, toCodePoints } from '../../utils/textUtils.js';
+import { assumeExhaustive } from '../../../utils/checks.js';
 
 // Check if we're at the end of a base word (on the last base character)
 // Returns true if current position has a base character followed only by combining marks until non-word
@@ -806,7 +807,7 @@ export function handleVimAction(
 
     default: {
       // This should never happen if TypeScript is working correctly
-      const _exhaustiveCheck: never = action;
+      assumeExhaustive(action);
       return state;
     }
   }

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);
+}