From c2d30e714fe439ca7847b197bf42e02ca7e45709 Mon Sep 17 00:00:00 2001
From: Klaus Meinhardt <klaus.meinhardt1@gmail.com>
Date: Sun, 13 Oct 2019 21:21:06 +0200
Subject: [PATCH] factory: parenthesize for-of expression when necessary

Fixes: #33856
---
 src/compiler/factory.ts                          |  2 +-
 .../reference/nullishCoalescingOperator12.js     | 10 ++++++++++
 .../nullishCoalescingOperator12.symbols          | 12 ++++++++++++
 .../reference/nullishCoalescingOperator12.types  | 16 ++++++++++++++++
 .../nullishCoalescingOperator12.ts               |  5 +++++
 5 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/nullishCoalescingOperator12.js
 create mode 100644 tests/baselines/reference/nullishCoalescingOperator12.symbols
 create mode 100644 tests/baselines/reference/nullishCoalescingOperator12.types
 create mode 100644 tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts

diff --git a/src/compiler/factory.ts b/src/compiler/factory.ts
index e7314eaafa5fc..27bc356946aad 100644
--- a/src/compiler/factory.ts
+++ b/src/compiler/factory.ts
@@ -1811,7 +1811,7 @@ namespace ts {
         const node = <ForOfStatement>createSynthesizedNode(SyntaxKind.ForOfStatement);
         node.awaitModifier = awaitModifier;
         node.initializer = initializer;
-        node.expression = expression;
+        node.expression = isCommaSequence(expression) ? createParen(expression) : expression;
         node.statement = asEmbeddedStatement(statement);
         return node;
     }
diff --git a/tests/baselines/reference/nullishCoalescingOperator12.js b/tests/baselines/reference/nullishCoalescingOperator12.js
new file mode 100644
index 0000000000000..f648af8e0b76b
--- /dev/null
+++ b/tests/baselines/reference/nullishCoalescingOperator12.js
@@ -0,0 +1,10 @@
+//// [nullishCoalescingOperator12.ts]
+const obj: { arr: any[] } = { arr: [] };
+for (const i of obj?.arr ?? []) { }
+
+
+//// [nullishCoalescingOperator12.js]
+"use strict";
+var _a, _b;
+const obj = { arr: [] };
+for (const i of (_b = (_a = obj) === null || _a === void 0 ? void 0 : _a.arr, (_b !== null && _b !== void 0 ? _b : []))) { }
diff --git a/tests/baselines/reference/nullishCoalescingOperator12.symbols b/tests/baselines/reference/nullishCoalescingOperator12.symbols
new file mode 100644
index 0000000000000..6be9ed5c5e49f
--- /dev/null
+++ b/tests/baselines/reference/nullishCoalescingOperator12.symbols
@@ -0,0 +1,12 @@
+=== tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts ===
+const obj: { arr: any[] } = { arr: [] };
+>obj : Symbol(obj, Decl(nullishCoalescingOperator12.ts, 0, 5))
+>arr : Symbol(arr, Decl(nullishCoalescingOperator12.ts, 0, 12))
+>arr : Symbol(arr, Decl(nullishCoalescingOperator12.ts, 0, 29))
+
+for (const i of obj?.arr ?? []) { }
+>i : Symbol(i, Decl(nullishCoalescingOperator12.ts, 1, 10))
+>obj?.arr : Symbol(arr, Decl(nullishCoalescingOperator12.ts, 0, 12))
+>obj : Symbol(obj, Decl(nullishCoalescingOperator12.ts, 0, 5))
+>arr : Symbol(arr, Decl(nullishCoalescingOperator12.ts, 0, 12))
+
diff --git a/tests/baselines/reference/nullishCoalescingOperator12.types b/tests/baselines/reference/nullishCoalescingOperator12.types
new file mode 100644
index 0000000000000..d0b52b7afbfa2
--- /dev/null
+++ b/tests/baselines/reference/nullishCoalescingOperator12.types
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts ===
+const obj: { arr: any[] } = { arr: [] };
+>obj : { arr: any[]; }
+>arr : any[]
+>{ arr: [] } : { arr: never[]; }
+>arr : never[]
+>[] : never[]
+
+for (const i of obj?.arr ?? []) { }
+>i : any
+>obj?.arr ?? [] : any[]
+>obj?.arr : any[]
+>obj : { arr: any[]; }
+>arr : any[]
+>[] : never[]
+
diff --git a/tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts b/tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts
new file mode 100644
index 0000000000000..500340380b8e5
--- /dev/null
+++ b/tests/cases/conformance/expressions/nullishCoalescingOperator/nullishCoalescingOperator12.ts
@@ -0,0 +1,5 @@
+// @strict: true
+// @target: ES2015
+
+const obj: { arr: any[] } = { arr: [] };
+for (const i of obj?.arr ?? []) { }