Print parentheses around identifier let where necessary (#13269)

packages/babel-generator/test/fixtures/edgecase/let-identifier/input.js

@@ -0,0 +1,31 @@
+/* ExpressionStatement */
+let;
+\u006cet[x];
+(let)[x];
+a[let[x]];
+
+/* ForStatement */
+for (let;;);
+for (\u006cet[x];;);
+for ((let)[x];;);
+for (a[let[x]];;);
+
+/* ForInStatement */
+for (let in {});
+for (\u006cet[x] in {});
+for ((let)[x] in {});
+for (a[let[x]] in {});
+
+/* ForOfStatement { await: false } */
+for ((let) of []);
+for (\u006cet of []);
+for ((let)[x] of []);
+for (a[let] of []);
+
+/* ForOfStatement { await: true } */
+async () => {
+  for await ((let) of []);
+  for await (\u006cet of []);
+  for await ((let)[x] of []);
+  for await (a[let] of []);
+}

packages/babel-generator/test/fixtures/edgecase/let-identifier/options.json

@@ -0,0 +1,4 @@
+{
+  "sourceType": "script",
+  "strictMode": false
+}

packages/babel-generator/test/fixtures/edgecase/let-identifier/output.js

@@ -0,0 +1,46 @@
+/* ExpressionStatement */
+let;
+(let)[x];
+(let)[x];
+a[let[x]];
+/* ForStatement */
+
+for (let;;);
+
+for ((let)[x];;);
+
+for ((let)[x];;);
+
+for (a[let[x]];;);
+/* ForInStatement */
+
+
+for (let in {});
+
+for ((let)[x] in {});
+
+for ((let)[x] in {});
+
+for (a[let[x]] in {});
+/* ForOfStatement { await: false } */
+
+
+for ((let) of []);
+
+for ((let) of []);
+
+for ((let)[x] of []);
+
+for (a[let] of []);
+/* ForOfStatement { await: true } */
+
+
+async () => {
+  for await ((let) of []);
+
+  for await ((let) of []);
+
+  for await ((let)[x] of []);
+
+  for await (a[let] of []);
+};

packages/babel-generator/test/index.js

@@ -763,6 +763,18 @@ describe("programmatic generation", function () {
       expect(output).toBe("interface A {}");
     });
   });
+
+  describe("identifier let", () => {
+    it("detects open bracket from non-optional OptionalMemberExpression", () => {
+      const ast = parse(`for (let?.[x];;);`, {
+        sourceType: "script",
+        strictMode: "false",
+      });
+      ast.program.body[0].init.optional = false;
+      const output = generate(ast).code;
+      expect(output).toBe("for ((let)[x];;);");
+    });
+  });
 });
 
 describe("CodeGenerator", function () {