New: Add prefer-regex-literals rule (fixes #12238)

docs/rules/prefer-regex-literals.md

@@ -0,0 +1,90 @@
+# Disallow use of the `RegExp` constructor in favor of regular expression literals (prefer-regex-literals)
+
+There are two ways to create a regular expression:
+
+* Regular expression literals, e.g. `/abc/u`.
+* The `RegExp` constructor function, e.g. `new RegExp("abc", "u")` or `RegExp("abc", "u")`.
+
+The constructor function is particularly useful when you want to dynamically generate the pattern,
+because it takes string arguments.
+
+When using the constructor function with string literals, don't forget that the string escaping rules still apply.
+If you want to put a backslash in the pattern, you need to escape it in the string literal.
+Thus, the following are equivalent:
+
+```js
+new RegExp("^\\d\\.$");
+
+/^\d\.$/;
+
+// matches "0.", "1.", "2." ... "9."
+```
+
+In the above example, the regular expression literal is easier to read and reason about.
+Also, it's a common mistake to omit the extra `\` in the string literal, which would produce a completely different regular expression:
+
+```js
+new RegExp("^\d\.$");
+
+// equivalent to /^d.$/, matches "d1", "d2", "da", "db" ...
+```
+
+When a regular expression is known in advance, it is considered a best practice to avoid the string literal notation on top
+of the regular expression notation, and use regular expression literals instead of the constructor function.
+
+## Rule Details
+
+This rule disallows the use of the `RegExp` constructor function with string literals as its arguments.
+
+This rule also disallows the use of the `RegExp` constructor function with template literals without expressions
+and `String.raw` tagged template literals without expressions.
+
+The rule does not disallow all use of the `RegExp` constructor. It should be still used for
+dynamically generated regular expressions.
+
+Examples of **incorrect** code for this rule:
+
+```js
+new RegExp("abc");
+
+new RegExp("abc", "u");
+
+RegExp("abc");
+
+RegExp("abc", "u");
+
+new RegExp("\\d\\d\\.\\d\\d\\.\\d\\d\\d\\d");
+
+RegExp(`^\\d\\.$`);
+
+new RegExp(String.raw`^\d\.$`);
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/abc/;
+
+/abc/u;
+
+/\d\d\.\d\d\.\d\d\d\d/;
+
+/^\d\.$/;
+
+// RegExp constructor is allowed for dynamically generated regular expressions
+
+new RegExp(pattern);
+
+RegExp("abc", flags);
+
+new RegExp(prefix + "abc");
+
+RegExp(`${prefix}abc`);
+
+new RegExp(String.raw`^\d\. ${sufix}`);
+```
+
+## Further Reading
+
+* [MDN: Regular Expressions](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions)
+* [MDN: RegExp Constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp)

lib/rules/index.js

@@ -242,6 +242,7 @@ module.exports = new LazyLoadingRuleMap(Object.entries({
     "prefer-object-spread": () => require("./prefer-object-spread"),
     "prefer-promise-reject-errors": () => require("./prefer-promise-reject-errors"),
     "prefer-reflect": () => require("./prefer-reflect"),
+    "prefer-regex-literals": () => require("./prefer-regex-literals"),
     "prefer-rest-params": () => require("./prefer-rest-params"),
     "prefer-spread": () => require("./prefer-spread"),
     "prefer-template": () => require("./prefer-template"),

lib/rules/prefer-regex-literals.js

@@ -0,0 +1,109 @@
+/**
+ * @fileoverview Rule to disallow use of the `RegExp` constructor in favor of regular expression literals
+ * @author Milos Djermanovic
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+const { CALL, CONSTRUCT, ReferenceTracker } = require("eslint-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Determines whether the given node is a string literal.
+ * @param {ASTNode} node Node to check.
+ * @returns {boolean} True if the node is a string literal.
+ */
+function isStringLiteral(node) {
+    return node.type === "Literal" && typeof node.value === "string";
+}
+
+/**
+ * Determines whether the given node is a template literal without expressions.
+ * @param {ASTNode} node Node to check.
+ * @returns {boolean} True if the node is a template literal without expressions.
+ */
+function isStaticTemplateLiteral(node) {
+    return node.type === "TemplateLiteral" && node.expressions.length === 0;
+}
+
+/**
+ * Determines whether the given node is a String.raw`` tagged template expression
+ * with a static template literal.
+ * @param {ASTNode} node Node to check.
+ * @returns {boolean} True if the node is String.raw`` with a static template.
+ */
+function isStringRawTaggedStaticTemplateLiteral(node) {
+    return node.type === "TaggedTemplateExpression" &&
+        node.tag.type === "MemberExpression" &&
+        node.tag.object.type === "Identifier" && node.tag.object.name === "String" &&
+        astUtils.getStaticPropertyName(node.tag) === "raw" &&
+        isStaticTemplateLiteral(node.quasi);
+}
+
+/**
+ * Determines whether the given node is considered to be a static string by the logic of this rule.
+ * @param {ASTNode} node Node to check.
+ * @returns {boolean} True if the node is a static string.
+ */
+function isStaticString(node) {
+    return isStringLiteral(node) ||
+        isStaticTemplateLiteral(node) ||
+        isStringRawTaggedStaticTemplateLiteral(node);
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "suggestion",
+
+        docs: {
+            description: "disallow use of the `RegExp` constructor in favor of regular expression literals",
+            category: "Best Practices",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/prefer-regex-literals"
+        },
+
+        schema: [],
+
+        messages: {
+            unexpectedRegExp: "Use a regular expression literal instead of the 'RegExp' constructor."
+        }
+    },
+
+    create(context) {
+        return {
+            Program() {
+                const scope = context.getScope();
+                const tracker = new ReferenceTracker(scope);
+                const traceMap = {
+                    RegExp: {
+                        [CALL]: true,
+                        [CONSTRUCT]: true
+                    }
+                };
+
+                for (const { node } of tracker.iterateGlobalReferences(traceMap)) {
+                    const args = node.arguments;
+
+                    if (
+                        (args.length === 1 || args.length === 2) &&
+                        args.every(isStaticString)
+                    ) {
+                        context.report({ node, messageId: "unexpectedRegExp" });
+                    }
+                }
+            }
+        };
+    }
+};