From 565731668f8d4797e163eba812f4dac77cf63648 Mon Sep 17 00:00:00 2001
From: Simen Bekkhus <sbekkhus91@gmail.com>
Date: Mon, 21 Jan 2019 17:26:39 +0100
Subject: [PATCH] fix: do not format callbacks with arguments as React hooks
 (#5778)

Ref: https://github.com/prettier/prettier/pull/5608#issuecomment-455860396
---
 CHANGELOG.unreleased.md                       | 37 +++++++++++++++++++
 src/language-js/printer-estree.js             |  1 +
 .../__snapshots__/jsfmt.spec.js.snap          | 15 ++++++++
 tests/break-calls/break.js                    |  8 ++++
 4 files changed, 61 insertions(+)

diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 7b5a8f5be..e3d39b97e 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -41,3 +41,40 @@ Examples:
   ```
 
 -->
+
+- JavaScript: Do not format functions with arguments as react hooks ([#5778] by [@SimenB])
+
+  The formatting added in Prettier 1.16 would format any function receiving an
+  arrow function and an array literal to match React Hook's documentation.
+  Prettier will now format this the same as before that change if the arrow
+  function receives any arguments.
+
+  <!-- prettier-ignore -->
+  ```js
+  // Input
+  ["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce(
+    (allColors, color) => {
+      return allColors.concat(color);
+    },
+    []
+  );
+
+  // Output (Prettier stable)
+  ["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce((
+    allColors,
+    color
+  ) => {
+    return allColors.concat(color);
+  }, []);
+
+  // Output (Prettier master)
+  ["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce(
+    (allColors, color) => {
+      return allColors.concat(color);
+    },
+    []
+  );
+  ```
+
+[@simenb]: https://github.com/SimenB
+[#5778]: https://github.com/prettier/prettier/pull/5778
diff --git a/src/language-js/printer-estree.js b/src/language-js/printer-estree.js
index 6dc595828..fcfabfffb 100644
--- a/src/language-js/printer-estree.js
+++ b/src/language-js/printer-estree.js
@@ -3904,6 +3904,7 @@ function printArgumentsList(path, options, print) {
   if (
     args.length === 2 &&
     args[0].type === "ArrowFunctionExpression" &&
+    args[0].params.length === 0 &&
     args[0].body.type === "BlockStatement" &&
     args[1].type === "ArrayExpression" &&
     !args.find(arg => arg.leadingComments || arg.trailingComments)
diff --git a/tests/break-calls/__snapshots__/jsfmt.spec.js.snap b/tests/break-calls/__snapshots__/jsfmt.spec.js.snap
index ca9195dca..35c0b97e7 100644
--- a/tests/break-calls/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/break-calls/__snapshots__/jsfmt.spec.js.snap
@@ -42,6 +42,14 @@ const mapChargeItems = fp.flow(
 
 expect(new LongLongLongLongLongRange([0, 0], [0, 0])).toEqualAtomLongLongLongLongRange(new LongLongLongRange([0, 0], [0, 0]));
 
+["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce(
+  (allColors, color) => {
+    return allColors.concat(color);
+  },
+  []
+);
+
+
 =====================================output=====================================
 h(
   f(
@@ -84,6 +92,13 @@ expect(
   new LongLongLongLongLongRange([0, 0], [0, 0])
 ).toEqualAtomLongLongLongLongRange(new LongLongLongRange([0, 0], [0, 0]));
 
+["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce(
+  (allColors, color) => {
+    return allColors.concat(color);
+  },
+  []
+);
+
 ================================================================================
 `;
 
diff --git a/tests/break-calls/break.js b/tests/break-calls/break.js
index b2a98ca97..9edd24456 100644
--- a/tests/break-calls/break.js
+++ b/tests/break-calls/break.js
@@ -33,3 +33,11 @@ const mapChargeItems = fp.flow(
 );
 
 expect(new LongLongLongLongLongRange([0, 0], [0, 0])).toEqualAtomLongLongLongLongRange(new LongLongLongRange([0, 0], [0, 0]));
+
+["red", "white", "blue", "black", "hotpink", "rebeccapurple"].reduce(
+  (allColors, color) => {
+    return allColors.concat(color);
+  },
+  []
+);
+