From 292b1c0017bc442d399f67e01d699c59e6b71453 Mon Sep 17 00:00:00 2001
From: Milos Djermanovic <milos.djermanovic@gmail.com>
Date: Fri, 15 Jan 2021 18:33:06 +0100
Subject: [PATCH] Fix: no-extra-parens false positive with `let` identifier in
 for-loop (#13981)

---
 lib/rules/no-extra-parens.js       |  16 +++
 tests/lib/rules/no-extra-parens.js | 175 +++++++++++++++++++++++++++++
 2 files changed, 191 insertions(+)

diff --git a/lib/rules/no-extra-parens.js b/lib/rules/no-extra-parens.js
index 8d358d23ad3..19c6fced79d 100644
--- a/lib/rules/no-extra-parens.js
+++ b/lib/rules/no-extra-parens.js
@@ -895,6 +895,22 @@ module.exports = {
                 }
 
                 if (node.init) {
+
+                    if (node.init.type !== "VariableDeclaration") {
+                        const firstToken = sourceCode.getFirstToken(node.init, astUtils.isNotOpeningParenToken);
+
+                        if (
+                            firstToken.value === "let" &&
+                            astUtils.isOpeningBracketToken(
+                                sourceCode.getTokenAfter(firstToken, astUtils.isNotClosingParenToken)
+                            )
+                        ) {
+
+                            // ForStatement#init expression cannot start with `let[`.
+                            tokensToIgnore.add(firstToken);
+                        }
+                    }
+
                     startNewReportsBuffering();
 
                     if (hasExcessParens(node.init)) {
diff --git a/tests/lib/rules/no-extra-parens.js b/tests/lib/rules/no-extra-parens.js
index 3fee9fefd8f..43c66c7562a 100644
--- a/tests/lib/rules/no-extra-parens.js
+++ b/tests/lib/rules/no-extra-parens.js
@@ -599,6 +599,22 @@ ruleTester.run("no-extra-parens", rule, {
             options: ["functions"]
         },
         "(let)[foo]",
+
+        // ForStatement#init expression cannot start with `let[`. It would be parsed as a `let` declaration with array pattern, or a syntax error.
+        "for ((let[a]);;);",
+        "for ((let)[a];;);",
+        "for ((let[a] = 1);;);",
+        "for ((let[a]) = 1;;);",
+        "for ((let)[a] = 1;;);",
+        "for ((let[a, b] = foo);;);",
+        "for ((let[a].b = 1);;);",
+        "for ((let[a].b) = 1;;);",
+        "for ((let[a]).b = 1;;);",
+        "for ((let)[a].b = 1;;);",
+        "for ((let[a])();;);",
+        "for ((let)[a]();;);",
+        "for ((let[a]) + b;;);",
+
         "for ((let) in foo);",
         "for ((let[foo]) in bar);",
         "for ((let)[foo] in bar);",
@@ -1880,6 +1896,165 @@ ruleTester.run("no-extra-parens", rule, {
             "Identifier",
             1
         ),
+
+        // ForStatement#init expression cannot start with `let[`, but it can start with `let` if it isn't followed by `[`
+        invalid(
+            "for ((let);;);",
+            "for (let;;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let = 1);;);",
+            "for (let = 1;;);",
+            "AssignmentExpression",
+            1
+        ),
+        invalid(
+            "for ((let) = 1;;);",
+            "for (let = 1;;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let = []);;);",
+            "for (let = [];;);",
+            "AssignmentExpression",
+            1
+        ),
+        invalid(
+            "for ((let) = [];;);",
+            "for (let = [];;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let());;);",
+            "for (let();;);",
+            "CallExpression",
+            1
+        ),
+        invalid(
+            "for ((let([]));;);",
+            "for (let([]);;);",
+            "CallExpression",
+            1
+        ),
+        invalid(
+            "for ((let())[a];;);",
+            "for (let()[a];;);",
+            "CallExpression",
+            1
+        ),
+        invalid(
+            "for ((let`[]`);;);",
+            "for (let`[]`;;);",
+            "TaggedTemplateExpression",
+            1
+        ),
+        invalid(
+            "for ((let.a);;);",
+            "for (let.a;;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for ((let).a;;);",
+            "for (let.a;;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let).a = 1;;);",
+            "for (let.a = 1;;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let).a[b];;);",
+            "for (let.a[b];;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for ((let.a)[b];;);",
+            "for (let.a[b];;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for ((let.a[b]);;);",
+            "for (let.a[b];;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for ((let);[];);",
+            "for (let;[];);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for (((let[a]));;);",
+            "for ((let[a]);;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for (((let))[a];;);",
+            "for ((let)[a];;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for (((let[a])).b;;);",
+            "for ((let[a]).b;;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for (((let))[a].b;;);",
+            "for ((let)[a].b;;);",
+            "Identifier",
+            1
+        ),
+        invalid(
+            "for (((let)[a]).b;;);",
+            "for ((let)[a].b;;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for (((let[a]) = b);;);",
+            "for ((let[a]) = b;;);",
+            "AssignmentExpression",
+            1
+        ),
+        invalid(
+            "for (((let)[a]) = b;;);",
+            "for ((let)[a] = b;;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for (((let)[a] = b);;);",
+            "for ((let)[a] = b;;);",
+            "AssignmentExpression",
+            1
+        ),
+        invalid(
+            "for ((Let[a]);;);",
+            "for (Let[a];;);",
+            "MemberExpression",
+            1
+        ),
+        invalid(
+            "for ((lett)[a];;);",
+            "for (lett[a];;);",
+            "Identifier",
+            1
+        ),
+
         invalid(
             "for ((let.foo) in bar);",
             "for (let.foo in bar);",