1 files changed, 90 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/mark-exported-symbols-as-used.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/mark-exported-symbols-as-used.js
new file mode 100644
index 0000000000..5d0e57e4c8
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/mark-exported-symbols-as-used.js
@@ -0,0 +1,90 @@
+/**
+ * @fileoverview Simply marks exported symbols as used. Designed for use in
+ * .jsm files only.
+ *
+ * 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";
+
+function markArrayElementsAsUsed(context, node, expression) {
+  if (expression.type != "ArrayExpression") {
+    context.report({
+      node,
+      messageId: "nonArrayAssignedToImported",
+    });
+    return;
+  }
+
+  for (let element of expression.elements) {
+    context.markVariableAsUsed(element.value);
+  }
+  // Also mark EXPORTED_SYMBOLS as used.
+  context.markVariableAsUsed("EXPORTED_SYMBOLS");
+}
+
+// Ignore assignments not in the global scope, e.g. where special module
+// definitions are required due to having different ways of importing files,
+// e.g. osfile.
+function isGlobalScope(context) {
+  return !context.getScope().upper;
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/mark-exported-symbols-as-used.html",
+    },
+    messages: {
+      useLetForExported:
+        "EXPORTED_SYMBOLS cannot be declared via `let`. Use `var` or `this.EXPORTED_SYMBOLS =`",
+      nonArrayAssignedToImported:
+        "Unexpected assignment of non-Array to EXPORTED_SYMBOLS",
+    },
+    schema: [],
+    type: "problem",
+  },
+
+  create(context) {
+    return {
+      AssignmentExpression(node, parents) {
+        if (
+          node.operator === "=" &&
+          node.left.type === "MemberExpression" &&
+          node.left.object.type === "ThisExpression" &&
+          node.left.property.name === "EXPORTED_SYMBOLS" &&
+          isGlobalScope(context)
+        ) {
+          markArrayElementsAsUsed(context, node, node.right);
+        }
+      },
+
+      VariableDeclaration(node, parents) {
+        if (!isGlobalScope(context)) {
+          return;
+        }
+
+        for (let item of node.declarations) {
+          if (
+            item.id &&
+            item.id.type == "Identifier" &&
+            item.id.name === "EXPORTED_SYMBOLS"
+          ) {
+            if (node.kind === "let") {
+              // The use of 'let' isn't allowed as the lexical scope may die after
+              // the script executes.
+              context.report({
+                node,
+                messageId: "useLetForExported",
+              });
+            }
+
+            markArrayElementsAsUsed(context, node, item.init);
+          }
+        }
+      },
+    };
+  },
+};