Merge pull request #1361 from benjamn/fix/enclose-unary-expression-in…

…side-exponentiation-in-parens

fix(print): wrap unary exprs inside `**` in parens

lib/fast-path.ts

@@ -355,6 +355,17 @@ FPp.needsParens = function (assumeExpressionContext) {
 
   if (!parent) return false;
 
+  // Wrap e.g. `-1` in parentheses inside `(-1) ** 2`.
+  if (
+    node.type === "UnaryExpression" &&
+    parent.type === "BinaryExpression" &&
+    name === "left" &&
+    parent.left === node &&
+    parent.operator === "**"
+  ) {
+    return true;
+  }
+
   switch (node.type) {
     case "UnaryExpression":
     case "SpreadElement":

test/printer.ts

@@ -2031,6 +2031,27 @@ describe("printer", function () {
     assert.strictEqual(pretty, code);
   });
 
+  for (const operator of ["-", "+", "~", "!", "typeof", "void"] as const) {
+    it(`adds parenthesis around '${operator}' unary expression in exponentiation expression`, function () {
+      const code = `(${
+        /[a-z]/.test(operator) ? `${operator} ` : operator
+      }a) ** 2;`;
+      const ast = b.program([
+        b.expressionStatement(
+          b.binaryExpression(
+            "**",
+            b.unaryExpression(operator, b.identifier("a"), true),
+            b.literal(2),
+          ),
+        ),
+      ]);
+
+      const printer = new Printer();
+      const pretty = printer.print(ast).code;
+      assert.strictEqual(pretty, code);
+    });
+  }
+
   it("prints flow object type internal slots correctly", function () {
     const code = [
       "type MyObjectType = {",