fix(javascript): correctly handle comments in empty arrow function expressions (#6086)

CHANGELOG.unreleased.md

@@ -95,6 +95,20 @@ console.log(
 );
 ```
 
+### JavaScript: Correctly handle comments in empty arrow function expressions ([#6086] by [@evilebottnawi])
+
+<!-- prettier-ignore -->
+```js
+// Input
+const fn = (/*event, data*/) => doSomething(anything);
+
+// Output (Prettier stable)
+const fn = () => /*event, data*/ doSomething(anything);
+
+// Output (Prettier master)
+const fn = (/*event, data*/) => doSomething(anything);
+```
+
 ### TypeScript: Keep trailing comma in tsx type parameters ([#6115] by [@sosukesuzuki])
 
 Previously, a trailing comma after single type parameter in arrow function was cleaned up. The formatted result is valid as ts, but is invalid as tsx. Prettier master fixes this issue.
@@ -203,6 +217,7 @@ This changes the method of finding the required count of backticks from using 2
 ````
 
 [#5979]: https://github.com/prettier/prettier/pull/5979
+[#6086]: https://github.com/prettier/prettier/pull/6086
 [#6088]: https://github.com/prettier/prettier/pull/6088
 [#6115]: https://github.com/prettier/prettier/pull/6115
 [#6106]: https://github.com/prettier/prettier/pull/6106

src/language-js/comments.js

@@ -558,9 +558,7 @@ function handleCommentInEmptyParens(text, enclosingNode, comment, options) {
     enclosingNode &&
     (((enclosingNode.type === "FunctionDeclaration" ||
       enclosingNode.type === "FunctionExpression" ||
-      (enclosingNode.type === "ArrowFunctionExpression" &&
-        (enclosingNode.body.type !== "CallExpression" ||
-          enclosingNode.body.arguments.length === 0)) ||
+      enclosingNode.type === "ArrowFunctionExpression" ||
       enclosingNode.type === "ClassMethod" ||
       enclosingNode.type === "ObjectMethod") &&
       enclosingNode.params.length === 0) ||

tests/comments/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,23 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`arrow.js 1`] = `
+====================================options=====================================
+parsers: ["flow", "babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+const fn = (/*event, data*/) => doSomething();
+
+const fn2 = (/*event, data*/) => doSomething(anything);
+
+=====================================output=====================================
+const fn = (/*event, data*/) => doSomething();
+
+const fn2 = (/*event, data*/) => doSomething(anything);
+
+================================================================================
+`;
+
 exports[`assignment-pattern.js 1`] = `
 ====================================options=====================================
 parsers: ["flow", "babel"]

tests/comments/arrow.js

@@ -0,0 +1,3 @@
+const fn = (/*event, data*/) => doSomething();
+
+const fn2 = (/*event, data*/) => doSomething(anything);