docs update

docs/_custom-rule-tutorial-code/.eslintrc.js

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+"use strict";
+
+module.exports = {
+    env: {
+        browser: true,
+        commonjs: true,
+        es2021: true,
+    },
+    extends: ["eslint:recommended"],
+    parserOptions: {
+        ecmaVersion: "latest",
+        ecmaFeatures: {
+            strict: true,
+        }
+    },
+    // Using the eslint-plugin-foo-bar plugin downloaded from npm
+    plugins: ["foo-bar"],
+    rules: {
+        "foo-bar/foo-bar": "error",
+    },
+}

docs/_custom-rule-tutorial-code/.gitignore

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+node_modules

docs/_custom-rule-tutorial-code/eslint-plugin-foo-bar.js

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+"use strict";
+
+const fooBarRule = require("./foo-bar");
+module.exports = { rules: { "foo-bar": fooBarRule } };

docs/_custom-rule-tutorial-code/example.js

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+"use strict";
+
+/* eslint-disable no-unused-vars -- Disable other rule causing problem for this file */
+
+// To see the error in the terminal, run the following command:
+// npx eslint example.js
+
+// To fix the error, run the following command:
+// npx eslint example.js --fix
+
+function correctFooBar() {
+  const foo = "bar";
+}
+
+function incorrectFoo(){
+  const foo = "baz"; // Problem!
+}
+

docs/_custom-rule-tutorial-code/foo-bar.js

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+"use strict";
+
+// The foo-bar rule definition
+module.exports = {
+    meta: {
+        type: "fix",
+        docs: {
+            description: "Can only assign 'bar' to `const foo`.",
+        },
+         fixable: "code"
+    },
+    create: function (context) {
+        return {
+            // Performs action in the function on every variable declaration
+            "VariableDeclaration": function(node) {
+                // Check if a `const` variable declaration
+                if(node.kind === "const") {
+                    // Check if variable name is `foo`
+                    if(node.declarations[0].id.name === "foo") {
+                        // Check if value of variable is "bar"
+                        if (node.declarations[0].init.value !== "bar") {
+                            // Report error to ESLint. Error message uses
+                            // a message placeholder to include the incorrect value
+                            // in the error message.
+                            // Also includes a `fix(fixer)` function that replaces
+                            // any values assigned to `const foo` with "bar".
+                            context.report({
+                                node,
+                                message: 'Value other than "bar" assigned to `const foo`. Unexpected value: {{ notBar }}',
+                                data: {
+                                    notBar: node.declarations[0].init.value
+                                },
+                                fix(fixer) {
+                                    return fixer.replaceText(node.declarations[0].init, '"bar"');
+                                }
+                            });
+                        }
+                    }
+                }
+            }
+        };
+    }
+};

docs/_custom-rule-tutorial-code/foo-bar.test.js

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+"use strict";
+
+const {RuleTester} = require("eslint");
+const fooBarRule = require("./foo-bar");
+
+const ruleTester = new RuleTester({
+  // Must use at least ecmaVersion 2015 because
+  // that's when `const` variable introduced.
+  parserOptions: { ecmaVersion: 2015 }
+});
+
+// Throws error if the tests in ruleTester.run() do not pass
+ruleTester.run(
+  "foo-bar", // rule name
+  fooBarRule, // rule code
+  { // checks
+    // 'valid' checks cases that should pass
+    valid: [{
+      code: "const foo = 'bar';",
+    }],
+    // 'invalid' checks cases that should not pass
+    invalid: [{
+      code:"const foo = 'baz';",
+      output: 'const foo = "bar";',
+      errors: 1,
+    }],
+  }
+);
+
+console.log("All tests passed!");