Port over copyright rule

.oxlintrc.json

@@ -29,6 +29,10 @@
     "builtin": true
   },
   "rules": {
+    "element-call/copyright-header": [
+      "error",
+      "/*\nCopyright %%CURRENT_YEAR%% New Vector Ltd.\n\nSPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial\nPlease see LICENSE in the repository root for full details.\n*/\n\n"
+    ],
     "element-call/no-observablescope-leak": "error",
     "jsdoc/empty-tags": "error",
     "jsdoc/check-property-names": "error",

eslint/CopyrightHeader.js

@@ -0,0 +1,66 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { ESLintUtils } from "@typescript-eslint/utils";
+
+const rule = ESLintUtils.RuleCreator(
+  () => "https://github.com/element-hq/element-call",
+)({
+  name: "copyright-header",
+  meta: {
+    type: "problem",
+    fixable: "code",
+    docs: {
+      description: "Require a copyright header in files.",
+    },
+    messages: {
+      noHeader: "Copyright header is required.",
+    },
+    schema: [{ type: "string" }],
+  },
+  create(context) {
+    const code = context.getSourceCode();
+
+    return {
+      Program(node) {
+        const firstToken = code.getFirstToken(node, { includeComments: false });
+
+        if (!firstToken) {
+          return;
+        }
+
+        const headComments = code.getCommentsBefore(firstToken);
+        const hasSomeCopyrightHeader = headComments?.some((comment) =>
+          comment?.value?.includes("Copyright"),
+        );
+        if (hasSomeCopyrightHeader) {
+          return;
+        }
+        const headerTemplate = context.options[0];
+        const fix = headerTemplate
+          ? function (fixer) {
+              return fixer.insertTextBefore(
+                firstToken,
+                headerTemplate.replace(
+                  /%%CURRENT_YEAR%%/g,
+                  new Date().getFullYear(),
+                ),
+              );
+            }
+          : undefined;
+
+        context.report({
+          messageId: "noHeader",
+          node,
+          fix,
+        });
+      },
+    };
+  },
+});
+
+export default rule;

eslint/index.js

@@ -1,5 +1,6 @@
 module.exports = {
   rules: {
+    "copyright-header": require("./CopyrightHeader").default,
     "no-observablescope-leak": require("./NoObservableScopeLeak").default,
   },
 };