Install dependencies, add configs

.editorconfig

@@ -4,16 +4,17 @@
 
 root = true
 
+
 [*]
 end_of_line = lf
 charset = utf-8
 trim_trailing_whitespace = true
 insert_final_newline = true
 indent_style = space
 indent_size = 2
+max_line_length = 100
 
 [*.hbs]
-insert_final_newline = false
 
 [*.{diff,md}]
 trim_trailing_whitespace = false

.eslintignore

@@ -8,13 +8,15 @@
 
 # dependencies
 /bower_components/
-/node_modules/
 
 # misc
 /coverage/
-!.*
 
 # ember-try
 /.node_modules.ember-try/
 /bower.json.ember-try
 /package.json.ember-try
+
+# IDE
+/.idea/
+/.history/

.eslintrc.js

@@ -1,58 +1,127 @@
 'use strict';
 
+const nodeFiles = [
+  '.eslintrc.js',
+  '.lintstagedrc.js',
+  '.prettierrc.js',
+  '.template-lintrc.{js,ts}',
+  'ember-cli-build.{js,ts}',
+  'testem.{js,ts}',
+  'blueprints/*/index.{js,ts}',
+  'config/**/*.{js,ts}',
+  'lib/*/index.{js,ts}',
+  'server/**/*.{js,ts}',
+];
+
+const browserFiles = [
+  'addon/**/*.{js,ts}',
+  'addon-test-support/**/*.{js,ts}',
+  'app/**/*.{js,ts}',
+  'test-support/**/*.{js,ts}',
+  'types/**/*.{js,ts}',
+];
+
+const browserTestFiles = ['tests/**/*.{js,ts}'];
+
 module.exports = {
   root: true,
-  parser: 'babel-eslint',
+  parser: '@typescript-eslint/parser',
   parserOptions: {
     ecmaVersion: 2018,
     sourceType: 'module',
-    ecmaFeatures: {
-      legacyDecorators: true
-    }
+    project: ['./tsconfig.json', './tsconfig-node.json'],
   },
-  plugins: [
-    'ember'
-  ],
+  plugins: ['@typescript-eslint', 'ember', 'prettier'],
   extends: [
     'eslint:recommended',
-    'plugin:ember/recommended'
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+    'plugin:@typescript-eslint/recommended-requiring-type-checking',
+    'plugin:ember/recommended',
+    'standard',
+
+    'prettier/@typescript-eslint',
+    'prettier/standard',
+
+    // This one should come last
+    'plugin:prettier/recommended',
   ],
   env: {
-    browser: true
+    browser: true,
   },
   rules: {
-    'ember/no-jquery': 'error'
+    '@typescript-eslint/ban-ts-ignore': 'off', // Can't fully get rid of it due to TS quirks and issues with third-party depenecies
+    '@typescript-eslint/camelcase': 'off', // Allow two levels of separation, e. g. ProductWizard_SidebarConfig_ListWithHeader_Component_Args
+    '@typescript-eslint/class-name-casing': 'off', // Allow two levels of separation, e. g. ProductWizard_SidebarConfig_ListWithHeader_Component_Args
+    '@typescript-eslint/no-empty-function': 'off', // Noop is a valid technique.
+    '@typescript-eslint/no-empty-interface': 'off', // Required for simplified typing of Mirage and Ember Data
+    '@typescript-eslint/no-non-null-assertion': 'off', // When I do it, I mean it.
+    '@typescript-eslint/no-unsafe-assignment': 'off', // Reenabled for TS files only
+    '@typescript-eslint/no-unsafe-call': 'off', // Reenabled for TS files only
+    '@typescript-eslint/no-unsafe-member-access': 'off', // Reenabled for TS files only
+    '@typescript-eslint/no-unsafe-return': 'off', // Reenabled for TS files only
+    '@typescript-eslint/no-unused-expressions': 'off', // Reenabled for non-tests only (Chai needs this disabled)
+    '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
+    '@typescript-eslint/no-var-requires': 'off', // Reenabled for non-Node files only
+
+    // As this rule would freak out on JS files (by design!),
+    // it has to be enabled only for .ts in the overrides section,
+    // See https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-function-return-type.md#configuring-in-a-mixed-jsts-codebase
+    '@typescript-eslint/explicit-function-return-type': 'off',
+
+    camelcase: 'off', // Have to keep this off for the TS equivalent to take precedence
+    'no-console': ['error', { allow: ['debug', 'error', 'info', 'warn'] }],
+    'no-unused-expressions': 'off',
+    'no-useless-constructor': 'off', // This rule crashes ESLint unless disabled
+
+    'node/no-unpublished-require': 'off', // Reenabled for non-Node files only
+
+    'prefer-const': 'error', // Only use `let` when you are actually mutating the variable
+    'prettier/prettier': 'error',
   },
   overrides: [
     // node files
     {
-      files: [
-        '.eslintrc.js',
-        '.template-lintrc.js',
-        'ember-cli-build.js',
-        'index.js',
-        'testem.js',
-        'blueprints/*/index.js',
-        'config/**/*.js',
-        'tests/dummy/config/**/*.js'
-      ],
-      excludedFiles: [
-        'addon/**',
-        'addon-test-support/**',
-        'app/**',
-        'tests/dummy/app/**'
-      ],
+      files: nodeFiles,
       parserOptions: {
-        sourceType: 'script'
+        sourceType: 'script',
       },
       env: {
         browser: false,
-        node: true
+        node: true,
       },
       plugins: ['node'],
-      rules: Object.assign({}, require('eslint-plugin-node').configs.recommended.rules, {
+      rules: {
+        ...require('eslint-plugin-node').configs.recommended.rules, // eslint-disable-line node/no-unpublished-require
         // add your custom rules and overrides for node files here
-      })
-    }
-  ]
+        'node/no-unsupported-features/es-syntax': ['error', { version: '>=12.0.0' }],
+      },
+    },
+    {
+      // browser files, including tests
+      files: [...browserFiles, ...browserTestFiles],
+      rules: {
+        '@typescript-eslint/no-var-requires': 'error', // Reenabled for non-Node files only
+        'node/no-unpublished-require': 'error', // Reenabled for non-Node files only
+      },
+    },
+    {
+      /// non-tests
+      files: [...nodeFiles, ...browserFiles],
+      rules: {
+        '@typescript-eslint/no-unused-expressions': 'error', // Reenabled for non-tests only (Chai needs this disabled)
+      },
+    },
+    {
+      // TS files
+      files: ['*.ts'],
+      rules: {
+        '@typescript-eslint/explicit-function-return-type': 'error', // We want to be strict with types
+        '@typescript-eslint/no-unsafe-assignment': 'error', // Reenabled for TS files only
+        '@typescript-eslint/no-unsafe-call': 'error', // Reenabled for TS files only
+        '@typescript-eslint/no-unsafe-member-access': 'error', // Reenabled for TS files only
+        '@typescript-eslint/no-unsafe-return': 'error', // Reenabled for TS files only
+      },
+    },
+  ],
 };

.gitignore

@@ -9,8 +9,6 @@
 /node_modules/
 
 # misc
-/.env*
-/.pnp*
 /.sass-cache
 /connect.lock
 /coverage/
@@ -23,3 +21,7 @@
 /.node_modules.ember-try/
 /bower.json.ember-try
 /package.json.ember-try
+
+# IDE
+/.idea/
+/.history/

.lintstagedrc.js

@@ -0,0 +1,17 @@
+'use strict';
+
+module.exports = {
+  // Run TSC on all the codebase.
+  // Can't run TSC on individual files because we have two envs: Node and browser,
+  // and TSC does not support providing a config and a path to a specific file at the same time.
+  // Thus, two separate configs are used: one for Node, one for browser.
+  // The function allows running the command globally, rather than once per each staged file.
+  '{addon,addon-test-support,app,mirage,test-support,tests,types}/**/*.ts': () => 'yarn lint:ts -p tsconfig.json',
+  '{*,.*,blueprints/*/*,config/**/*,lib/*/index,server/**/*}.{js,ts}': () => 'yarn lint:ts -p tsconfig-node.json',
+
+  // Run ESLint, typescript-eslint and Prettier on staged files only
+  '**/*.{js,ts}': ['yarn lint:eslint --fix'],
+
+  // Template lint
+  '**/*.hbs': ['yarn ember-template-lint'],
+};

.prettierrc.js

@@ -0,0 +1,6 @@
+module.exports = {
+  arrowParens: 'always', // It's convenient that you don't have to add them by hand when you need to add more args or a type
+  singleQuote: true,     // Enabled to align with EmberJS Prettier config
+  printWidth: 100,       // Per team's agreement
+  trailingComma: 'es5',  // Trailing commas makes editing easier, diffs cleaner. `es5` option aligns with EmberJS Prettier config
+};

.template-lintrc.js

@@ -1,5 +1,5 @@
 'use strict';
 
 module.exports = {
-  extends: 'octane'
+  extends: 'recommended'
 };