Add missing parentheses to let in for..of loop (#14044)

Co-authored-by: Georgii Dolzhykov <thorn.mailbox@gmail.com>

changelog_unreleased/javascript/14000.md

@@ -1,4 +1,4 @@
-#### Fix missing parentheses when an expression statement starts with `let[` (#14000 by @fisker, @thorn0)
+#### Fix missing parentheses when an expression statement starts with `let[` (#14000, #14044 by @fisker, @thorn0)
 
 <!-- prettier-ignore -->
 ```jsx

src/language-js/needs-parens.js

@@ -67,16 +67,32 @@ function needsParens(path, options) {
       return true;
     }
 
-    // `for (async of []);` is invalid
+    // `for ((async) of []);` and `for ((let) of []);`
     if (
       name === "left" &&
-      node.name === "async" &&
+      (node.name === "async" || node.name === "let") &&
       parent.type === "ForOfStatement" &&
       !parent.await
     ) {
       return true;
     }
 
+    // `for ((let.a) of []);`
+    if (node.name === "let") {
+      const expression = path.findAncestor(
+        (node) => node.type === "ForOfStatement"
+      )?.left;
+      if (
+        expression &&
+        startsWithNoLookaheadToken(
+          expression,
+          (leftmostNode) => leftmostNode === node
+        )
+      ) {
+        return true;
+      }
+    }
+
     // `(let)[a] = 1`
     if (
       name === "object" &&
@@ -89,8 +105,7 @@ function needsParens(path, options) {
         (node) =>
           node.type === "ExpressionStatement" ||
           node.type === "ForStatement" ||
-          node.type === "ForInStatement" ||
-          node.type === "ForOfStatement"
+          node.type === "ForInStatement"
       );
       const expression = !statement
         ? undefined

tests/format/js/identifier/for-of/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,57 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`await.js format 1`] = `
+====================================options=====================================
+parsers: ["babel", "typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+async function a() {
+  for await((let).a of foo);
+  for await((let)[a] of foo);
+  for await((let)()[a] of foo);
+}
+
+=====================================output=====================================
+async function a() {
+  for await ((let).a of foo);
+  for await ((let)[a] of foo);
+  for await ((let)()[a] of foo);
+}
+
+================================================================================
+`;
+
+exports[`let.js format 1`] = `
+====================================options=====================================
+parsers: ["babel", "typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+for ((let) of foo);
+for (foo of let);
+for (foo of let.a);
+for (foo of let[a]);
+for ((let.a) of foo);
+for ((let[a]) of foo);
+for ((let)().a of foo);
+for (letFoo of foo);
+
+for ((let.a) in foo);
+for ((let[a]) in foo);
+
+=====================================output=====================================
+for ((let) of foo);
+for (foo of let);
+for (foo of let.a);
+for (foo of let[a]);
+for ((let).a of foo);
+for ((let)[a] of foo);
+for ((let)().a of foo);
+for (letFoo of foo);
+
+for (let.a in foo);
+for ((let)[a] in foo);
+
+================================================================================
+`;

tests/format/js/identifier/for-of/await.js

@@ -0,0 +1,5 @@
+async function a() {
+  for await((let).a of foo);
+  for await((let)[a] of foo);
+  for await((let)()[a] of foo);
+}

tests/format/js/identifier/for-of/jsfmt.spec.js

@@ -0,0 +1,5 @@
+run_spec(__dirname, [
+  "babel",
+  // "flow",
+  "typescript",
+]);

tests/format/js/identifier/for-of/let.js

@@ -0,0 +1,11 @@
+for ((let) of foo);
+for (foo of let);
+for (foo of let.a);
+for (foo of let[a]);
+for ((let.a) of foo);
+for ((let[a]) of foo);
+for ((let)().a of foo);
+for (letFoo of foo);
+
+for ((let.a) in foo);
+for ((let[a]) in foo);