From f7b26d18cbb507a868e7edc2b66515da64d814e2 Mon Sep 17 00:00:00 2001
From: Mathias Schreck <schreck.mathias@gmail.com>
Date: Wed, 29 Jan 2020 14:55:19 +0100
Subject: [PATCH] Update: prefer-regex-literal detect regex literals (fixes
 #12840)

The rule `prefer-regex-literal` now detects when regex literals are
unnecessarily passed to the `RegExp` constructor.
---
 lib/rules/prefer-regex-literals.js       | 27 ++++++++++++++++++++----
 tests/lib/rules/prefer-regex-literals.js |  9 ++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/lib/rules/prefer-regex-literals.js b/lib/rules/prefer-regex-literals.js
index 47b2b090f829..bc5c9497dba1 100644
--- a/lib/rules/prefer-regex-literals.js
+++ b/lib/rules/prefer-regex-literals.js
@@ -25,6 +25,15 @@ function isStringLiteral(node) {
     return node.type === "Literal" && typeof node.value === "string";
 }
 
+/**
+ * Determines whether the given node is a regex literal.
+ * @param {ASTNode} node Node to check.
+ * @returns {boolean} True if the node is a regex literal.
+ */
+function isRegexLiteral(node) {
+    return node.type === "Literal" && Object.prototype.hasOwnProperty.call(node, "regex");
+}
+
 /**
  * Determines whether the given node is a template literal without expressions.
  * @param {ASTNode} node Node to check.
@@ -98,6 +107,15 @@ module.exports = {
                 isStringRawTaggedStaticTemplateLiteral(node);
         }
 
+        /**
+         * Determines whether the given node is considered to be a static string literal or a regex literal
+         * @param {ASTNode} node Node to check.
+         * @returns {boolean} True if the node is a static string or a regex literal
+         */
+        function isStaticPattern(node) {
+            return isStaticString(node) || isRegexLiteral(node);
+        }
+
         return {
             Program() {
                 const scope = context.getScope();
@@ -112,10 +130,11 @@ module.exports = {
                 for (const { node } of tracker.iterateGlobalReferences(traceMap)) {
                     const args = node.arguments;
 
-                    if (
-                        (args.length === 1 || args.length === 2) &&
-                        args.every(isStaticString)
-                    ) {
+                    if (args.length === 1 && isStaticPattern(args[0])) {
+                        context.report({ node, messageId: "unexpectedRegExp" });
+                    }
+
+                    if (args.length === 2 && isStaticPattern(args[0]) && isStaticString(args[1])) {
                         context.report({ node, messageId: "unexpectedRegExp" });
                     }
                 }
diff --git a/tests/lib/rules/prefer-regex-literals.js b/tests/lib/rules/prefer-regex-literals.js
index e263ef03dc7a..6a472ebe81bc 100644
--- a/tests/lib/rules/prefer-regex-literals.js
+++ b/tests/lib/rules/prefer-regex-literals.js
@@ -41,6 +41,7 @@ ruleTester.run("prefer-regex-literals", rule, {
         "new RegExp(String.raw`a${''}c`);",
         "new RegExp('a' + 'b')",
         "RegExp(1)",
+        "new RegExp(/a/, flags);",
 
         // invalid number of arguments
         "new RegExp;",
@@ -177,6 +178,14 @@ ruleTester.run("prefer-regex-literals", rule, {
         {
             code: "RegExp('a', String.raw`g`);",
             errors: [{ messageId: "unexpectedRegExp", type: "CallExpression" }]
+        },
+        {
+            code: "new RegExp(/a/);",
+            errors: [{ messageId: "unexpectedRegExp", type: "NewExpression", line: 1, column: 1 }]
+        },
+        {
+            code: "new RegExp(/a/, 'u');",
+            errors: [{ messageId: "unexpectedRegExp", type: "NewExpression", line: 1, column: 1 }]
         }
     ]
 });