1 files changed, 155 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-isInstance.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-isInstance.js
new file mode 100644
index 0000000000..ffd9bc9566
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+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-isInstance.js
@@ -0,0 +1,155 @@
+/**
+ * @fileoverview Reject use of instanceof against DOM interfaces
+ *
+ * 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";
+
+const fs = require("fs");
+
+const { maybeGetMemberPropertyName } = require("../helpers");
+
+const privilegedGlobals = Object.keys(
+  require("../environments/privileged.js").globals
+);
+
+// -----------------------------------------------------------------------------
+// Rule Definition
+// -----------------------------------------------------------------------------
+
+/**
+ * Whether an identifier is defined by eslint configuration.
+ * `env: { browser: true }` or `globals: []` for example.
+ * @param {import("eslint-scope").Scope} currentScope
+ * @param {import("estree").Identifier} id
+ */
+function refersToEnvironmentGlobals(currentScope, id) {
+  const reference = currentScope.references.find(ref => ref.identifier === id);
+  const { resolved } = reference || {};
+  if (!resolved) {
+    return false;
+  }
+
+  // No definition in script files; defined via .eslintrc
+  return resolved.scope.type === "global" && resolved.defs.length === 0;
+}
+
+/**
+ * Whether a node points to a DOM interface.
+ * Includes direct references to interfaces objects and also indirect references
+ * via property access.
+ * OS.File and lazy.(Foo) are explicitly excluded.
+ *
+ * @example HTMLElement
+ * @example win.HTMLElement
+ * @example iframe.contentWindow.HTMLElement
+ * @example foo.HTMLElement
+ *
+ * @param {import("eslint-scope").Scope} currentScope
+ * @param {import("estree").Node} node
+ */
+function pointsToDOMInterface(currentScope, node) {
+  if (node.type === "MemberExpression") {
+    const objectName = maybeGetMemberPropertyName(node.object);
+    if (objectName === "lazy") {
+      // lazy.Foo is probably a non-IDL import.
+      return false;
+    }
+    if (objectName === "OS" && node.property.name === "File") {
+      // OS.File is an exception that is not a Web IDL interface
+      return false;
+    }
+    // For `win.Foo`, `iframe.contentWindow.Foo`, or such.
+    return privilegedGlobals.includes(node.property.name);
+  }
+
+  if (
+    node.type === "Identifier" &&
+    refersToEnvironmentGlobals(currentScope, node)
+  ) {
+    return privilegedGlobals.includes(node.name);
+  }
+
+  return false;
+}
+
+/**
+ * @param {import("eslint").Rule.RuleContext} context
+ */
+function isChromeContext(context) {
+  const filename = context.getFilename();
+  const isChromeFileName =
+    filename.endsWith(".sys.mjs") || filename.endsWith(".jsm");
+  if (isChromeFileName) {
+    return true;
+  }
+
+  if (filename.endsWith(".xhtml")) {
+    // Treat scripts in XUL files as chrome scripts
+    // Note: readFile is needed as getSourceCode() only gives JS blocks
+    return fs.readFileSync(filename).includes("there.is.only.xul");
+  }
+
+  // Treat scripts as chrome privileged when using:
+  // 1. ChromeUtils, but not SpecialPowers.ChromeUtils
+  // 2. BrowserTestUtils, PlacesUtils
+  // 3. document.createXULElement
+  // 4. loader.lazyRequireGetter
+  // 5. Services.foo, but not SpecialPowers.Services.foo
+  // 6. evalInSandbox
+  const source = context.getSourceCode().text;
+  return !!source.match(
+    /(^|\s)ChromeUtils|BrowserTestUtils|PlacesUtils|createXULElement|lazyRequireGetter|(^|\s)Services\.|evalInSandbox/
+  );
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/use-isInstance.html",
+    },
+    fixable: "code",
+    messages: {
+      preferIsInstance:
+        "Please prefer .isInstance() in chrome scripts over the standard instanceof operator for DOM interfaces, " +
+        "since the latter will return false when the object is created from a different context.",
+    },
+    schema: [],
+    type: "problem",
+  },
+  /**
+   * @param {import("eslint").Rule.RuleContext} context
+   */
+  create(context) {
+    if (!isChromeContext(context)) {
+      return {};
+    }
+
+    return {
+      BinaryExpression(node) {
+        const { operator, right } = node;
+        if (
+          operator === "instanceof" &&
+          pointsToDOMInterface(context.getScope(), right)
+        ) {
+          context.report({
+            node,
+            messageId: "preferIsInstance",
+            fix(fixer) {
+              const sourceCode = context.getSourceCode();
+              return fixer.replaceText(
+                node,
+                `${sourceCode.getText(right)}.isInstance(${sourceCode.getText(
+                  node.left
+                )})`
+              );
+            },
+          });
+        }
+      },
+    };
+  },
+};