Add type annotations to arrow-parens "as-needed"

rules/arrow-parens.js

@@ -24,7 +24,9 @@ module.exports = function(context) {
         if (node.async) token = context.getTokenAfter(token);
 
         // as-needed: x => x
-        if (asNeeded && node.params.length === 1 && node.params[0].type === "Identifier") {
+        if (asNeeded && node.params.length === 1
+                && node.params[0].type === "Identifier"
+                && node.params[0].typeAnnotation === undefined) {
             if (token.type === "Punctuator" && token.value === "(") {
                 context.report(node, asNeededMessage);
             }
@@ -50,4 +52,4 @@ module.exports.schema = [
     {
         "enum": ["always", "as-needed"]
     }
-];
+];

tests/arrow-parens.js

@@ -46,6 +46,7 @@ var valid = [
     { code: "(a = 10) => {}", options: ["as-needed"], ecmaFeatures: { arrowFunctions: true, destructuring: true, defaultParams: true } },
     { code: "(...a) => a[0]", options: ["as-needed"], ecmaFeatures: { arrowFunctions: true, restParams: true } },
     { code: "(a, b) => {}", options: ["as-needed"], ecmaFeatures: { arrowFunctions: true } },
+    ok("(a: string) => a", ["as-needed"]),
 
     // async
     ok("async () => {}"),
@@ -174,4 +175,4 @@ var invalid = [
 ruleTester.run("arrow-parens", rule, {
     valid: valid,
     invalid: invalid
-});
+});