feat: support TypeScript syntax in default-param-last (#19431)

* feat: support TypeScript syntax in `default-param-last`

* Apply suggestions from code review

Co-authored-by: Nicholas C. Zakas <[email protected]>

* Simplify naming and runtime logic

* Added ```ts support to rule docs examples

* nit: parser name

* meta.docs.typescript: 'syntax'

* fix: example tooling tests

* Add: meta.dialects, language

* Remove the typescript: syntax

* Don't render playground links for ts code blocks

---------

Co-authored-by: Nicholas C. Zakas <[email protected]>

Author: JoshuaKGoldberg

docs/.eleventy.js

@@ -202,6 +202,14 @@ module.exports = function(eleventyConfig) {
     const ruleExampleOptions = markdownItRuleExample({
         open({ type, code, languageOptions, env, codeBlockToken }) {
 
+            /*
+             * TypeScript isn't yet supported on the playground:
+             * https://github.com/eslint/eslint.org/issues/709
+             */
+            if (codeBlockToken.info === "ts") {
+                return `<div class="${type}">`;
+            }
+
             prismESLintHook.addContentMustBeMarked(codeBlockToken.content, languageOptions);
 
             const isRuleRemoved = !Object.hasOwn(env.rules_meta, env.title);

docs/src/rules/default-param-last.md

@@ -41,6 +41,34 @@ Examples of **correct** code for this rule:
 /* eslint default-param-last: ["error"] */
 
 function f(a, b = 0) {}
+
+function g(a, b = 0, c = 0) {}
+```
+
+:::
+
+This rule additionally supports TypeScript type syntax.
+
+Examples of **incorrect** TypeScript code for this rule:
+
+::: incorrect
+
+```ts
+/* eslint default-param-last: ["error"] */
+
+function h(a = 0, b: number) {}
+```
+
+:::
+
+Examples of **correct** TypeScript code for this rule:
+
+::: correct
+
+```ts
+/* eslint default-param-last: ["error"] */
+
+function h(a = 0, b?: number) {}
 ```
 
 :::

lib/rules/default-param-last.js

@@ -5,9 +5,24 @@
 
 "use strict";
 
+/**
+ * Checks if node is required: i.e. does not have a default value or ? optional indicator.
+ * @param {ASTNode} node the node to be evaluated
+ * @returns {boolean} true if the node is required, false if not.
+ */
+function isRequiredParameter(node) {
+    return !(
+        node.type === "AssignmentPattern" ||
+        node.type === "RestElement" ||
+        node.optional
+    );
+}
+
 /** @type {import('../shared/types').Rule} */
 module.exports = {
     meta: {
+        dialects: ["javascript", "typescript"],
+        language: "javascript",
         type: "suggestion",
 
         docs: {
@@ -32,22 +47,23 @@ module.exports = {
          * @returns {void}
          */
         function handleFunction(node) {
-            let hasSeenPlainParam = false;
+            let hasSeenRequiredParameter = false;
 
             for (let i = node.params.length - 1; i >= 0; i -= 1) {
-                const param = node.params[i];
+                const current = node.params[i];
+                const param =
+                    current.type === "TSParameterProperty"
+                        ? current.parameter
+                        : current;
 
-                if (
-                    param.type !== "AssignmentPattern" &&
-                    param.type !== "RestElement"
-                ) {
-                    hasSeenPlainParam = true;
+                if (isRequiredParameter(param)) {
+                    hasSeenRequiredParameter = true;
                     continue;
                 }
 
-                if (hasSeenPlainParam && param.type === "AssignmentPattern") {
+                if (hasSeenRequiredParameter) {
                     context.report({
-                        node: param,
+                        node: current,
                         messageId: "shouldBeLast"
                     });
                 }

tests/fixtures/bad-examples.md

@@ -17,7 +17,7 @@ export default "foo";
 
 :::correct
 
-````ts
+````rs
 const foo = "bar";
 
 const foo = "baz";