Bug 1625500 - tell people to use promise.finally() instead of passing 2 identical things to .then, r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D68613

tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js

@@ -134,6 +134,7 @@ module.exports = {
     "mozilla/use-chromeutils-generateqi": "error",
     "mozilla/use-chromeutils-import": "error",
     "mozilla/use-default-preference-values": "error",
+    "mozilla/use-finally": "error",
     "mozilla/use-includes-instead-of-indexOf": "error",
     "mozilla/use-ownerGlobal": "error",
     "mozilla/use-returnValue": "error",

tools/lint/eslint/eslint-plugin-mozilla/lib/index.js

@@ -61,6 +61,7 @@ module.exports = {
     "use-chromeutils-generateqi": require("../lib/rules/use-chromeutils-generateqi"),
     "use-chromeutils-import": require("../lib/rules/use-chromeutils-import"),
     "use-default-preference-values": require("../lib/rules/use-default-preference-values"),
+    "use-finally": require("../lib/rules/use-finally"),
     "use-ownerGlobal": require("../lib/rules/use-ownerGlobal"),
     "use-includes-instead-of-indexOf": require("../lib/rules/use-includes-instead-of-indexOf"),
     "use-returnValue": require("../lib/rules/use-returnValue"),

tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-finally.js

@@ -0,0 +1,54 @@
+/**
+ * @fileoverview Require .finally() instead of .then(x, x)
+ *
+ * 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";
+
+// -----------------------------------------------------------------------------
+// Rule Definition
+// -----------------------------------------------------------------------------
+
+module.exports = function(context) {
+  // ---------------------------------------------------------------------------
+  // Public
+  //  --------------------------------------------------------------------------
+
+  return {
+    CallExpression(node) {
+      if (
+        node.callee.type == "MemberExpression" &&
+        node.callee.property.name == "then" &&
+        node.arguments.length == 2
+      ) {
+        let sourceCode = context.getSourceCode();
+        let firstArg = sourceCode.getText(node.arguments[0]);
+        let secondArg = sourceCode.getText(node.arguments[1]);
+        if (
+          firstArg == secondArg ||
+          firstArg.replace(/\s+/g, "") == secondArg.replace(/\s+/g, "")
+        ) {
+          context.report({
+            node,
+            message:
+              "Use .finally instead of passing 2 identical arguments to .then",
+            fix(fixer) {
+              let endNode = node.arguments[1];
+              let comments = sourceCode.getCommentsBefore(endNode);
+              if (comments.length) {
+                endNode = comments[0];
+              }
+              return fixer.replaceTextRange(
+                [node.callee.property.start, endNode.start],
+                "finally("
+              );
+            },
+          });
+        }
+      }
+    },
+  };
+};

tools/lint/eslint/eslint-plugin-mozilla/tests/use-finally.js

@@ -0,0 +1,47 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+var rule = require("../lib/rules/use-finally");
+var RuleTester = require("eslint").RuleTester;
+
+const ruleTester = new RuleTester({ parserOptions: { ecmaVersion: 6 } });
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+let gError = [
+  {
+    message: `Use .finally instead of passing 2 identical arguments to .then`,
+    type: "CallExpression",
+  },
+];
+
+ruleTester.run("use-finally", rule, {
+  valid: ["foo.finally(a)", "foo.then(a)", "foo.then(() => {})"],
+  invalid: [
+    {
+      code: "foo.then(a, a);",
+      output: "foo.finally(a);",
+      errors: gError,
+    },
+    // ignore whitespace:
+    {
+      code: "foo.then(() =>   {}, () => {});",
+      output: "foo.finally(() => {});",
+      errors: gError,
+    },
+    // keep comments:
+    {
+      code: "foo.then(a, /* make sure we always do this */ a);",
+      output: "foo.finally(/* make sure we always do this */ a);",
+      errors: gError,
+    },
+  ],
+});