From cbcd24a5b2e859eb319047883ea3d11329c240b8 Mon Sep 17 00:00:00 2001
From: Kevin Gibbons <bakkot@gmail.com>
Date: Fri, 12 Oct 2018 09:33:47 -0700
Subject: [PATCH] Correct parentheses for mixed exp/mod (#5243)

Fixes #5238.

cc @duailibe for the [original change](https://github.com/prettier/prettier/pull/4413). I basically undid that PR because it didn't look to me like `shouldFlatten` made sense as the place to introduce the behavior it was going for, but I might have misunderstood something.
---
 src/common/util.js                                       | 9 ---------
 src/language-js/needs-parens.js                          | 4 ++--
 .../binary-expressions/__snapshots__/jsfmt.spec.js.snap  | 2 ++
 tests/binary-expressions/exp.js                          | 1 +
 4 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/src/common/util.js b/src/common/util.js
index 8c3d4c6f3..bf0e1fc56 100644
--- a/src/common/util.js
+++ b/src/common/util.js
@@ -267,10 +267,6 @@ const equalityOperators = {
   "===": true,
   "!==": true
 };
-const additiveOperators = {
-  "+": true,
-  "-": true
-};
 const multiplicativeOperators = {
   "*": true,
   "/": true,
@@ -284,11 +280,6 @@ const bitshiftOperators = {
 
 function shouldFlatten(parentOp, nodeOp) {
   if (getPrecedence(nodeOp) !== getPrecedence(parentOp)) {
-    // x + y % z --> (x + y) % z
-    if (nodeOp === "%" && !additiveOperators[parentOp]) {
-      return true;
-    }
-
     return false;
   }
 
diff --git a/src/language-js/needs-parens.js b/src/language-js/needs-parens.js
index d6432aeaf..b0e2c03d9 100644
--- a/src/language-js/needs-parens.js
+++ b/src/language-js/needs-parens.js
@@ -291,10 +291,10 @@ function needsParens(path, options) {
           }
 
           if (pp < np && no === "%") {
-            return !util.shouldFlatten(po, no);
+            return po === "+" || po === "-";
           }
 
-          // Add parenthesis when working with binary operators
+          // Add parenthesis when working with bitwise operators
           // It's not stricly needed but helps with code understanding
           if (util.isBitwiseOperator(po)) {
             return true;
diff --git a/tests/binary-expressions/__snapshots__/jsfmt.spec.js.snap b/tests/binary-expressions/__snapshots__/jsfmt.spec.js.snap
index cbb26b7c0..7fd9c65c2 100644
--- a/tests/binary-expressions/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/binary-expressions/__snapshots__/jsfmt.spec.js.snap
@@ -101,6 +101,7 @@ a ** -b;
 -(a**b);
 (a * b) ** c;
 a ** (b * c);
+(a % b) ** c;
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 a ** (b ** c);
 (a ** b) ** c;
@@ -110,6 +111,7 @@ a ** -b;
 -(a ** b);
 (a * b) ** c;
 a ** (b * c);
+(a % b) ** c;
 
 `;
 
diff --git a/tests/binary-expressions/exp.js b/tests/binary-expressions/exp.js
index 903466894..e0bac4a5f 100644
--- a/tests/binary-expressions/exp.js
+++ b/tests/binary-expressions/exp.js
@@ -6,3 +6,4 @@ a ** -b;
 -(a**b);
 (a * b) ** c;
 a ** (b * c);
+(a % b) ** c;