warn about ts file extension

Summary: remove statically analysable life from typescript guidelines and let eslint handle it

Reviewed By: passy

Differential Revision: D33819891

fbshipit-source-id: 3cc3cb512607c3651cd3a9e48228d83bab5bb64a

desktop/.eslintrc.js

@@ -144,6 +144,7 @@ module.exports = {
     'flipper/no-relative-imports-across-packages': [2],
     'flipper/no-electron-remote-imports': [1],
     'flipper/no-console-error-without-context': [2],
+    'flipper/no-ts-file-extension': 1,
     'communist-spelling/communist-spelling': [1, {allow: ['cancelled']}],
 
     // promise rules, see https://github.com/xjamundx/eslint-plugin-promise for details on each of them

desktop/eslint-plugin-flipper/src/index.ts

@@ -16,11 +16,15 @@ import noElectronRemoteImports, {
 import noConsoleErrorWithoutContext, {
   RULE_NAME as noConsoleErrorWithoutContextRuleName,
 } from './rules/noConsoleErrorWithoutContext';
+import noTsFileExtension, {
+  RULE_NAME as noTsFileExtensionRuleName,
+} from './rules/noTsFileExtension';
 
 module.exports = {
   rules: {
     [noRelativeImportsAcrossPackagesRuleName]: noRelativeImportsAcrossPackages,
     [noElectronRemoteImportsRuleName]: noElectronRemoteImports,
     [noConsoleErrorWithoutContextRuleName]: noConsoleErrorWithoutContext,
+    [noTsFileExtensionRuleName]: noTsFileExtension,
   },
 };

desktop/eslint-plugin-flipper/src/rules/noTsFileExtension.ts

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import path from 'path';
+import {createESLintRule} from '../utils/createEslintRule';
+
+type Options = [];
+
+export type MessageIds = 'noTsFileExtension';
+export const RULE_NAME = 'no-ts-file-extension';
+
+export default createESLintRule<Options, MessageIds>({
+  name: RULE_NAME,
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Prefer "tsx" file extensions',
+      recommended: 'error',
+    },
+    schema: [],
+    messages: {
+      noTsFileExtension: 'Use "tsx" file extension instead of "ts"',
+    },
+  },
+  defaultOptions: [],
+  create(context) {
+    const filename = context.getFilename();
+    const ext = path.extname(filename);
+    const isTs = ext === '.ts' && !filename.endsWith('.d.ts');
+
+    return {
+      Program(node) {
+        if (isTs) {
+          context.report({
+            node: node,
+            messageId: 'noTsFileExtension',
+          });
+        }
+      },
+    };
+  },
+});

docs/extending/dev-setup.mdx

@@ -158,7 +158,6 @@ To start Flipper against a specific OnDemand instance, set FB_ONDEMAND flag, e.g
 </FbInternalOnly>
 
 ## Guidelines for writing TypeScript
-* **Important:** Use `.tsx` file extension for all TypeScript files (instead of `.ts`)
 * Prefer `type` for React props and state over interfaces
 * Don’t prefix interfaces with `I`
 * Enums, Types and Interfaces use PascalCase (uppercase first letter)