Fix parens issues with exponentiation in generator (#5830)

packages/babel-generator/src/node/parentheses.js

@@ -47,6 +47,13 @@ export function DoExpression(node: Object, parent: Object, printStack: Array<Obj
 }
 
 export function Binary(node: Object, parent: Object): boolean {
+  if (
+    node.operator === "**" &&
+    t.isBinaryExpression(parent, { operator: "**" })
+  ) {
+    return parent.left === node;
+  }
+
   if (
     ((t.isCallExpression(parent) || t.isNewExpression(parent)) && parent.callee === node) ||
     t.isUnaryLike(parent) ||
@@ -124,7 +131,8 @@ export function ClassExpression(node: Object, parent: Object, printStack: Array<
 export function UnaryLike(node: Object, parent: Object): boolean {
   return t.isMemberExpression(parent, { object: node }) ||
          t.isCallExpression(parent, { callee: node }) ||
-         t.isNewExpression(parent, { callee: node });
+         t.isNewExpression(parent, { callee: node }) ||
+         t.isBinaryExpression(parent, { operator: "**", left: node });
 }
 
 export function FunctionExpression(node: Object, parent: Object, printStack: Array<Object>): boolean {

packages/babel-generator/test/fixtures/parentheses/exponentiation/actual.js

@@ -0,0 +1,9 @@
+Math.sqrt(3**2 + (-5)**2);
+a ** b ** c;
+(a ** b) ** c;
+a.b ** c;
+(-a) ** b;
+a ** -b;
+-(a**b);
+(a * b) ** c;
+a ** (b * c);

packages/babel-generator/test/fixtures/parentheses/exponentiation/expected.js

@@ -0,0 +1,9 @@
+Math.sqrt(3 ** 2 + (-5) ** 2);
+a ** b ** c;
+(a ** b) ** c;
+a.b ** c;
+(-a) ** b;
+a ** -b;
+-(a ** b);
+(a * b) ** c;
+a ** (b * c);