From f1c6ed06d45fbc884d1a0293a90e58050c3d938a Mon Sep 17 00:00:00 2001
From: Ives van Hoorne <ives.v.h@gmail.com>
Date: Tue, 14 Jul 2020 15:45:01 +0200
Subject: [PATCH] Fix printing a double UnaryExpression

Fixes #4476
---
 .../__snapshots__/index.test.ts.snap          |  6 ++
 .../babel/convert-esmodule/generator.ts       | 61 +++++++++++++++++++
 .../babel/convert-esmodule/index.test.ts      |  8 +++
 3 files changed, 75 insertions(+)

diff --git a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/__snapshots__/index.test.ts.snap b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/__snapshots__/index.test.ts.snap
index 43dea6af0b2..3f12bc7d294 100644
--- a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/__snapshots__/index.test.ts.snap
+++ b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/__snapshots__/index.test.ts.snap
@@ -1,5 +1,11 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`convert-esmodule can convert + + 1`] = `
+"\\"use strict\\";
+c = (10, + +15);
+"
+`;
+
 exports[`convert-esmodule can convert class default exports 1`] = `
 "\\"use strict\\";
 Object.defineProperty(exports, \\"__esModule\\", {
diff --git a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/generator.ts b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/generator.ts
index 0bca48e7ee6..5d51094df0a 100644
--- a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/generator.ts
+++ b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/generator.ts
@@ -2,6 +2,39 @@ import * as astring from 'astring';
 import * as meriyah from 'meriyah';
 import { Identifier } from 'meriyah/dist/estree';
 
+// Enables parenthesis regardless of precedence
+const NEEDS_PARENTHESES = 17;
+const EXPRESSIONS_PRECEDENCE = {
+  // Definitions
+  ArrayExpression: 20,
+  TaggedTemplateExpression: 20,
+  ThisExpression: 20,
+  Identifier: 20,
+  Literal: 18,
+  TemplateLiteral: 20,
+  Super: 20,
+  SequenceExpression: 20,
+  // Operations
+  MemberExpression: 19,
+  CallExpression: 19,
+  NewExpression: 19,
+  // Other definitions
+  ArrowFunctionExpression: NEEDS_PARENTHESES,
+  ClassExpression: NEEDS_PARENTHESES,
+  FunctionExpression: NEEDS_PARENTHESES,
+  ObjectExpression: NEEDS_PARENTHESES,
+  // Other operations
+  UpdateExpression: 16,
+  UnaryExpression: 15,
+  BinaryExpression: 14,
+  LogicalExpression: 13,
+  ConditionalExpression: 4,
+  AssignmentExpression: 3,
+  AwaitExpression: 2,
+  YieldExpression: 2,
+  RestElement: 1,
+};
+
 /**
  * Add support for next syntax
  */
@@ -30,4 +63,32 @@ export const customGenerator = {
     this[node.source.type](node.source, state);
     state.write(')');
   },
+  UnaryExpression(
+    node: meriyah.ESTree.UnaryExpression,
+    state: { write(s: string): void }
+  ) {
+    if (node.prefix) {
+      state.write(node.operator);
+      if (
+        node.operator.length > 1 ||
+        node.argument.type === 'UnaryExpression'
+      ) {
+        state.write(' ');
+      }
+      if (
+        EXPRESSIONS_PRECEDENCE[node.argument.type] <
+        EXPRESSIONS_PRECEDENCE.UnaryExpression
+      ) {
+        state.write('(');
+        this[node.argument.type](node.argument, state);
+        state.write(')');
+      } else {
+        this[node.argument.type](node.argument, state);
+      }
+    } else {
+      // FIXME: This case never occurs
+      this[node.argument.type](node.argument, state);
+      state.write(node.operator);
+    }
+  },
 };
diff --git a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/index.test.ts b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/index.test.ts
index 062171ade63..4faf4c62732 100644
--- a/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/index.test.ts
+++ b/packages/app/src/sandbox/eval/transpilers/babel/convert-esmodule/index.test.ts
@@ -423,4 +423,12 @@ describe('convert-esmodule', () => {
 
     expect(convertEsModule(code)).toMatchSnapshot();
   });
+
+  it('can convert + +', () => {
+    const code = `
+    c = (10.0, + +(15))
+    `;
+
+    expect(convertEsModule(code)).toMatchSnapshot();
+  });
 });