Update: Allow regex in no-param-reassign ignore option array

docs/rules/no-param-reassign.md

@@ -34,7 +34,7 @@ function foo(bar) {
 
 ## Options
 
-This rule takes one option, an object, with a boolean property `"props"` and an array `"ignorePropertyModificationsFor"`. `"props"` is `false` by default. If `"props"` is set to `true`, this rule warns against the modification of parameter properties unless they're included in `"ignorePropertyModificationsFor"`, which is an empty array by default.
+This rule takes one option, an object, with a boolean property `"props"`, and  arrays `"ignorePropertyModificationsFor"` and `"ignorePropertyModificationsForRegex"`. `"props"` is `false` by default. If `"props"` is set to `true`, this rule warns against the modification of parameter properties unless they're included in `"ignorePropertyModificationsFor"` or `"ignorePropertyModificationsForRegex"`, which is an empty array by default.
 
 ### props
 
@@ -92,6 +92,24 @@ function foo(bar) {
 }
 ```
 
+Examples of **correct** code for the `{ "props": true }` option with `"ignorePropertyModificationsForRegex"` set:
+
+```js
+/*eslint no-param-reassign: ["error", { "props": true, "ignorePropertyModificationsForRegex": ["^bar"] }]*/
+
+function foo(bar) {
+    barVar.prop = "value";
+}
+
+function foo(bar) {
+    delete barrito.aaa;
+}
+
+function foo(bar) {
+    bar_.aaa++;
+}
+```
+
 
 ## When Not To Use It
 

lib/rules/no-param-reassign.js

@@ -45,6 +45,13 @@ module.exports = {
                                     type: "string"
                                 },
                                 uniqueItems: true
+                            },
+                            ignorePropertyModificationsForRegex: {
+                                type: "array",
+                                items: {
+                                    type: "string"
+                                },
+                                uniqueItems: true
                             }
                         },
                         additionalProperties: false
@@ -57,6 +64,7 @@ module.exports = {
     create(context) {
         const props = context.options[0] && context.options[0].props;
         const ignoredPropertyAssignmentsFor = context.options[0] && context.options[0].ignorePropertyModificationsFor || [];
+        const ignoredPropertyAssignmentsForRegex = context.options[0] && context.options[0].ignorePropertyModificationsForRegex || [];
 
         /**
          * Checks whether or not the reference modifies properties of its variable.
@@ -125,6 +133,19 @@ module.exports = {
             return false;
         }
 
+        /**
+         * Tests that an identifier name matches any of the ignored property assignments.
+         * First we test strings in ignoredPropertyAssignmentsFor.
+         * Then we instantiate and test RegExp objects from ignoredPropertyAssignmentsForRegex strings.
+         * @param {string} identifierName - A string that describes the name of an identifier to
+         * ignore property assignments for.
+         * @returns {boolean} Whether the string matches an ignored property assignment regular expression or not.
+         */
+        function isIgnoredPropertyAssignment(identifierName) {
+            return ignoredPropertyAssignmentsFor.includes(identifierName) ||
+                ignoredPropertyAssignmentsForRegex.some(ignored => new RegExp(ignored, "u").test(identifierName));
+        }
+
         /**
          * Reports a reference if is non initializer and writable.
          * @param {Reference} reference - A reference to check.
@@ -146,7 +167,7 @@ module.exports = {
             ) {
                 if (reference.isWrite()) {
                     context.report({ node: identifier, message: "Assignment to function parameter '{{name}}'.", data: { name: identifier.name } });
-                } else if (props && isModifyingProp(reference) && ignoredPropertyAssignmentsFor.indexOf(identifier.name) === -1) {
+                } else if (props && isModifyingProp(reference) && !isIgnoredPropertyAssignment(identifier.name)) {
                     context.report({ node: identifier, message: "Assignment to property of function parameter '{{name}}'.", data: { name: identifier.name } });
                 }
             }

tests/lib/rules/no-param-reassign.js

@@ -39,6 +39,11 @@ ruleTester.run("no-param-reassign", rule, {
         { code: "function foo(a) { delete a.b; }", options: [{ props: true, ignorePropertyModificationsFor: ["a"] }] },
         { code: "function foo(a, z) { a.b = 0; x.y = 0; }", options: [{ props: true, ignorePropertyModificationsFor: ["a", "x"] }] },
         { code: "function foo(a) { a.b.c = 0;}", options: [{ props: true, ignorePropertyModificationsFor: ["a"] }] },
+        { code: "function foo(aFoo) { aFoo.b = 0; }", options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$"] }] },
+        { code: "function foo(aFoo) { ++aFoo.b; }", options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$"] }] },
+        { code: "function foo(aFoo) { delete aFoo.b; }", options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$"] }] },
+        { code: "function foo(a, z) { aFoo.b = 0; x.y = 0; }", options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$", "^x.*$"] }] },
+        { code: "function foo(aFoo) { aFoo.b.c = 0;}", options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$"] }] },
         {
             code: "function foo(a) { ({ [a]: variable } = value) }",
             options: [{ props: true }],
@@ -106,6 +111,18 @@ ruleTester.run("no-param-reassign", rule, {
             parserOptions: { ecmaVersion: 6 },
             errors: [{ message: "Assignment to property of function parameter 'bar'." }]
         },
+        {
+            code: "function foo(bar) { [bar.a] = []; }",
+            options: [{ props: true, ignorePropertyModificationsForRegex: ["^a.*$"] }],
+            parserOptions: { ecmaVersion: 6 },
+            errors: [{ message: "Assignment to property of function parameter 'bar'." }]
+        },
+        {
+            code: "function foo(bar) { [bar.a] = []; }",
+            options: [{ props: true, ignorePropertyModificationsForRegex: ["^B.*$"] }],
+            parserOptions: { ecmaVersion: 6 },
+            errors: [{ message: "Assignment to property of function parameter 'bar'." }]
+        },
         {
             code: "function foo(bar) { ({foo: bar.a} = {}); }",
             options: [{ props: true }],