chore(eslint): convert eslint config to flat config (#376)

Co-authored-by: Thomas Bouffard <27200110+tbouffard@users.noreply.github.com>

Author: csouchet

.eslintignore

@@ -28,6 +28,7 @@ updates:
       # As the typescript version is old, it requires an old version of "@types/node".
       - dependency-name: "@types/node"
       # eslint v9 requires to first switch to flat configuration
+      - dependency-name: "@eslint/js"
       - dependency-name: "eslint"
       - dependency-name: "@types/eslint"
       # eslint-plugin-unicorn v57+ requires eslint v9 and flat configuration
@@ -41,10 +42,10 @@ updates:
             - "tailwindcss"
        lint:
           patterns:
-            - "@typescript-eslint/*"
             - "eslint-*"
             - "lint-staged"
             - "prettier"
+            - "typescript-eslint"
        test:
          patterns:
            - "@jest/*"

.eslintrc.cjs

@@ -0,0 +1,182 @@
+/*
+Copyright 2025 Bonitasoft S.A.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { readFileSync } from 'node:fs';
+import path from 'node:path';
+
+import eslint from '@eslint/js';
+import importPlugin from 'eslint-plugin-import';
+import jestPlugin from 'eslint-plugin-jest';
+import jestDomPlugin from 'eslint-plugin-jest-dom';
+import nodePlugin from 'eslint-plugin-n';
+import noticePlugin from 'eslint-plugin-notice';
+import prettierRecommendedConfig from 'eslint-plugin-prettier/recommended';
+import unicornPlugin from 'eslint-plugin-unicorn';
+// eslint-disable-next-line import/no-unresolved
+import tsEslint from 'typescript-eslint';
+
+const jestPackagePath = path.resolve('node_modules', 'jest', 'package.json');
+const jestPackage = JSON.parse(readFileSync(jestPackagePath, 'utf8'));
+
+export default tsEslint.config(
+  {
+    // Need to be in first before any other configuration
+    // https://eslint.org/docs/latest/use/configure/ignore
+    ignores: [
+      '.github/*',
+      '.idea/*',
+      // at project root, this directory includes a js template file used to add a license header with eslint in all files. It doesn't match the license rule because it is the template!
+      'config/*',
+      '**/coverage/*',
+      '**/dist/*',
+      '**/lib/*',
+      '**/node_modules/*',
+    ],
+  },
+
+  eslint.configs.recommended,
+
+  {
+    plugins: {
+      notice: noticePlugin,
+    },
+    rules: {
+      'notice/notice': ['error', { templateFile: 'config/license-header.js', onNonMatchingHeader: 'replace' }],
+      'no-console': ['error', { allow: ['warn', 'error'] }],
+    },
+  },
+
+  unicornPlugin.configs['flat/recommended'], // https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config
+
+  importPlugin.flatConfigs.recommended,
+  {
+    rules: {
+      // as defined in `bpmn-visualization` b122995c
+      'import/newline-after-import': ['error', { count: 1 }],
+      'import/first': 'error',
+      'import/order': [
+        'error',
+        {
+          groups: ['type', 'builtin', 'external', 'parent', 'sibling', 'index', 'internal'],
+          'newlines-between': 'always',
+          alphabetize: {
+            order: 'asc',
+            orderImportKind: 'asc',
+            caseInsensitive: true,
+          },
+        },
+      ],
+    },
+  },
+
+  // disable type-aware linting on JS files
+  {
+    files: ['**/*.{js,cjs,mjs}'],
+    ...tsEslint.configs.disableTypeChecked,
+  },
+
+  // typescript
+  tsEslint.configs.recommended,
+  tsEslint.configs.stylistic,
+
+  /** @type {import('@typescript-eslint').ConfigWithExtends} */
+  {
+    files: ['**/*.{ts,cts,mts}'],
+    ...importPlugin.flatConfigs.typescript,
+    settings: {
+      'import/resolver': {
+        typescript: {
+          alwaysTryTypes: true, // always try to resolve types under `<root>@types` directory even it doesn't contain any source code, like `@types/unist`
+          project: '**/tsconfig.json',
+        },
+      },
+    },
+    languageOptions: {
+      parser: tsEslint.parser,
+      parserOptions: {
+        // This setting is required if you want to use rules which require type information
+        // https://typescript-eslint.io/packages/parser/#project
+        project: ['./packages/**/tsconfig.json', './tsconfig.eslint.json'],
+      },
+    },
+    rules: {
+      '@typescript-eslint/explicit-function-return-type': [
+        'error',
+        {
+          allowExpressions: true,
+          allowTypedFunctionExpressions: true,
+        },
+      ],
+      '@typescript-eslint/explicit-member-accessibility': [
+        'error',
+        {
+          accessibility: 'no-public',
+        },
+      ],
+      '@typescript-eslint/consistent-type-exports': [
+        'error',
+        {
+          fixMixedExportsWithInlineTypeSpecifier: true,
+        },
+      ],
+      '@typescript-eslint/consistent-type-imports': ['error'],
+    },
+  },
+
+  // node plugin
+  {
+    ...nodePlugin.configs['flat/recommended-script'],
+    settings: {
+      node: {
+        allowModules: ['@process-analytics/bpmn-visualization-addons'],
+      },
+    },
+    rules: {
+      'n/file-extension-in-import': ['error', 'always'],
+    },
+  },
+
+  // for test files
+  {
+    files: ['**/test/**/*'],
+    ...jestPlugin.configs['flat/recommended'],
+    ...jestPlugin.configs['flat/style'],
+    ...jestDomPlugin.configs['flat/recommended'],
+    plugins: {
+      jest: jestPlugin,
+      'jest-dom': jestDomPlugin,
+    },
+    languageOptions: {
+      globals: jestPlugin.environments.globals.globals,
+    },
+    settings: {
+      jest: {
+        version: jestPackage.version,
+      },
+    },
+    rules: {
+      ...jestPlugin.configs['flat/recommended'].rules,
+      ...jestPlugin.configs['flat/style'].rules,
+      ...jestDomPlugin.configs['flat/recommended'].rules,
+      /* The rule list: https://github.com/jest-community/eslint-plugin-jest#rules */
+      'jest/prefer-expect-resolves': 'warn',
+      'jest/prefer-spy-on': 'warn',
+      'jest/prefer-todo': 'warn',
+    },
+  },
+
+  prettierRecommendedConfig, // Enables eslint-plugin-prettier, eslint-config-prettier and prettier/prettier. This will display prettier errors as ESLint errors. Make sure this is always the last configuration.
+);