1 files changed, 156 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-useless-parameters.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-useless-parameters.js
new file mode 100644
index 0000000000..ac1cc334e6
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/no-useless-parameters.js
@@ -0,0 +1,156 @@
+/**
+ * @fileoverview Reject common XPCOM methods called with useless optional
+ *               parameters, or non-existent parameters.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/no-useless-parameters.html",
+    },
+    fixable: "code",
+    messages: {
+      newURIParams: "newURI's last parameters are optional.",
+      obmittedWhenFalse:
+        "{{fnName}}'s {{index}} parameter can be omitted when it's false.",
+      onlyTakes: "{{fnName}} only takes {{params}}",
+    },
+    schema: [],
+    type: "suggestion",
+  },
+
+  create(context) {
+    function getRangeAfterArgToEnd(argNumber, args) {
+      let sourceCode = context.getSourceCode();
+      return [
+        sourceCode.getTokenAfter(args[argNumber]).range[0],
+        args[args.length - 1].range[1],
+      ];
+    }
+
+    return {
+      CallExpression(node) {
+        let callee = node.callee;
+        if (
+          callee.type !== "MemberExpression" ||
+          callee.property.type !== "Identifier"
+        ) {
+          return;
+        }
+
+        let isFalse = arg => arg.type === "Literal" && arg.value === false;
+        let isFalsy = arg => arg.type === "Literal" && !arg.value;
+        let isBool = arg =>
+          arg.type === "Literal" && (arg.value === false || arg.value === true);
+        let name = callee.property.name;
+        let args = node.arguments;
+
+        if (
+          ["addEventListener", "removeEventListener", "addObserver"].includes(
+            name
+          ) &&
+          args.length === 3 &&
+          isFalse(args[2])
+        ) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(1, args));
+            },
+            messageId: "obmittedWhenFalse",
+            data: { fnName: name, index: "third" },
+          });
+        }
+
+        if (name === "clearUserPref" && args.length > 1) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(0, args));
+            },
+            messageId: "onlyTakes",
+            data: { fnName: name, params: "1 parameter" },
+          });
+        }
+
+        if (name === "removeObserver" && args.length === 3 && isBool(args[2])) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(1, args));
+            },
+            messageId: "onlyTakes",
+            data: { fnName: name, params: "2 parameters" },
+          });
+        }
+
+        if (name === "appendElement" && args.length === 2 && isFalse(args[1])) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(0, args));
+            },
+            messageId: "obmittedWhenFalse",
+            data: { fnName: name, index: "second" },
+          });
+        }
+
+        if (
+          name === "notifyObservers" &&
+          args.length === 3 &&
+          isFalsy(args[2])
+        ) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(1, args));
+            },
+            messageId: "obmittedWhenFalse",
+            data: { fnName: name, index: "third" },
+          });
+        }
+
+        if (
+          name === "getComputedStyle" &&
+          args.length === 2 &&
+          isFalsy(args[1])
+        ) {
+          context.report({
+            node,
+            fix: fixer => {
+              return fixer.removeRange(getRangeAfterArgToEnd(0, args));
+            },
+            messageId: "obmittedWhenFalse",
+            data: { fnName: "getComputedStyle", index: "second" },
+          });
+        }
+
+        if (
+          name === "newURI" &&
+          args.length > 1 &&
+          isFalsy(args[args.length - 1])
+        ) {
+          context.report({
+            node,
+            fix: fixer => {
+              if (args.length > 2 && isFalsy(args[args.length - 2])) {
+                return fixer.removeRange(getRangeAfterArgToEnd(0, args));
+              }
+
+              return fixer.removeRange(
+                getRangeAfterArgToEnd(args.length - 2, args)
+              );
+            },
+            messageId: "newURIParams",
+          });
+        }
+      },
+    };
+  },
+};