chore: migrate to eslint flat config (#245)

Author: benmccann

.eslintignore

@@ -0,0 +1,108 @@
+import html from "eslint-plugin-html";
+import es from "eslint-plugin-es";
+import globals from "globals";
+import typescriptEslint from "@typescript-eslint/eslint-plugin";
+import tsParser from "@typescript-eslint/parser";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import js from "@eslint/js";
+import { FlatCompat } from "@eslint/eslintrc";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+export default [
+    { ignores: ["**/*\\{.,-}min.js", "docs/Chart.Financial.js"] },
+    ...compat.extends("chartjs", "plugin:es/restrict-to-es2018", "plugin:markdown/recommended"),
+    {
+        files: ["**/*.html"],
+        plugins: { html },
+    },
+    {
+        plugins: {
+            es
+        },
+
+        languageOptions: {
+            globals: {
+                ...globals.browser,
+                ...globals.node,
+
+                // TODO: it would be nicer to apply these only to tests
+                afterEach: "readonly",
+                describe: "readonly",
+                expect: "readonly",
+                it: "readonly"
+            },
+
+            ecmaVersion: 2022,
+            sourceType: "module",
+
+            parserOptions: {
+                ecmaFeatures: {
+                    impliedStrict: true,
+                    modules: true,
+                },
+            },
+        },
+
+        settings: {
+            es: {
+                aggressive: true,
+            },
+        },
+
+        rules: {
+            "class-methods-use-this": "off",
+            complexity: ["warn", 10],
+            "max-statements": ["warn", 30],
+            "no-empty-function": "off",
+
+            "no-use-before-define": ["error", {
+                functions: false,
+            }],
+
+            "es/no-import-meta": "off",
+            "es/no-async-iteration": "error",
+            "es/no-malformed-template-literals": "error",
+            "es/no-regexp-lookbehind-assertions": "error",
+            "es/no-regexp-named-capture-groups": "error",
+            "es/no-regexp-s-flag": "error",
+            "es/no-regexp-unicode-property-escapes": "error",
+            "es/no-dynamic-import": "off",
+        },
+    },
+    ...compat.extends("chartjs", "plugin:@typescript-eslint/recommended").map(config => ({
+        ...config,
+        files: ["**/*.ts"],
+    })),
+    {
+        files: ["**/*.ts"],
+
+        plugins: {
+            "@typescript-eslint": typescriptEslint,
+        },
+
+        languageOptions: {
+            parser: tsParser,
+        },
+
+        rules: {
+            complexity: ["warn", 10],
+            "max-statements": ["warn", 30],
+            indent: "off",
+            "@typescript-eslint/indent": ["error", 2],
+            "no-use-before-define": "off",
+            "@typescript-eslint/no-use-before-define": "error",
+            "no-shadow": "off",
+            "@typescript-eslint/no-shadow": "error",
+            "space-before-function-paren": "off",
+            "@typescript-eslint/space-before-function-paren": [2, "never"],
+        },
+    }
+];