From 49b0d0dfa9c4dcd641de738f7bf15a6001050210 Mon Sep 17 00:00:00 2001
From: Patrik Oldsberg <poldsberg@gmail.com>
Date: Thu, 12 Oct 2023 11:01:10 +0200
Subject: [PATCH] frontend-plugin-api: add helper for locating the callsite of
 a function

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
---
 .../routing/describeParentCallSite.test.ts    | 84 +++++++++++++++++++
 .../src/routing/describeParentCallSite.ts     | 59 +++++++++++++
 2 files changed, 143 insertions(+)
 create mode 100644 packages/frontend-plugin-api/src/routing/describeParentCallSite.test.ts
 create mode 100644 packages/frontend-plugin-api/src/routing/describeParentCallSite.ts

diff --git a/packages/frontend-plugin-api/src/routing/describeParentCallSite.test.ts b/packages/frontend-plugin-api/src/routing/describeParentCallSite.test.ts
new file mode 100644
index 0000000000..03a94dcb45
--- /dev/null
+++ b/packages/frontend-plugin-api/src/routing/describeParentCallSite.test.ts
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { describeParentCallSite } from './describeParentCallSite';
+
+class ChromeError {
+  name = 'Error';
+  message = 'eHgtF5hmbrXyiEvo';
+  get stack() {
+    return `Error: eHgtF5hmbrXyiEvo
+    at describeParentCallSite (describeParentCallSite.js:1:11)
+    at parent (parent.js:2:22)
+    at caller (parent-caller.js:3:33)
+    at other.js:3:33`;
+  }
+}
+
+class SafariError {
+  name = 'Error';
+  message = 'eHgtF5hmbrXyiEvo';
+  get stack() {
+    return `describeParentCallSite@describeParentCallSite.js:1:11
+parent@parent.js:2:22
+caller@parent-caller.js:3:33
+code@other.js:3:33`;
+  }
+}
+
+class FirefoxError {
+  name = 'Error';
+  message = 'eHgtF5hmbrXyiEvo';
+  get stack() {
+    return `describeParentCallSite@describeParentCallSite.js:1:11
+parent@parent.js:2:22
+caller@parent-caller.js:3:33
+@other.js:3:33
+`;
+  }
+}
+
+describe('describeParentCallSite', () => {
+  it('should work in Chrome', () => {
+    function myFactory() {
+      return describeParentCallSite(ChromeError);
+    }
+    function myCaller() {
+      return myFactory();
+    }
+    expect(myCaller()).toBe('parent-caller.js:3:33');
+  });
+
+  it('should work in Safari', () => {
+    function myFactory() {
+      return describeParentCallSite(SafariError);
+    }
+    function myCaller() {
+      return myFactory();
+    }
+    expect(myCaller()).toBe('parent-caller.js:3:33');
+  });
+
+  it('should work in Firefox', () => {
+    function myFactory() {
+      return describeParentCallSite(FirefoxError);
+    }
+    function myCaller() {
+      return myFactory();
+    }
+    expect(myCaller()).toBe('parent-caller.js:3:33');
+  });
+});
diff --git a/packages/frontend-plugin-api/src/routing/describeParentCallSite.ts b/packages/frontend-plugin-api/src/routing/describeParentCallSite.ts
new file mode 100644
index 0000000000..72997e07db
--- /dev/null
+++ b/packages/frontend-plugin-api/src/routing/describeParentCallSite.ts
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const MESSAGE_MARKER = 'eHgtF5hmbrXyiEvo';
+
+/**
+ * Internal helper that describes the location of the parent caller.
+ * @internal
+ */
+export function describeParentCallSite(
+  ErrorConstructor: { new (message: string): Error } = Error,
+): string {
+  const { stack } = new ErrorConstructor(MESSAGE_MARKER);
+  if (!stack) {
+    return '<unknown>';
+  }
+
+  // Safari and Firefox don't include the error itself in the stack
+  const startIndex = stack.includes(MESSAGE_MARKER)
+    ? stack.indexOf('\n') + 1
+    : 0;
+  const secondEntryStart =
+    stack.indexOf('\n', stack.indexOf('\n', startIndex) + 1) + 1;
+  const secondEntryEnd = stack.indexOf('\n', secondEntryStart);
+
+  const line = stack.substring(secondEntryStart, secondEntryEnd).trim();
+  if (!line) {
+    return 'unknown';
+  }
+
+  // Below we try to extract the location for different browsers.
+  // Since RouteRefs are declared at the top-level of modules the caller name isn't interesting.
+
+  // Chrome
+  if (line.includes('(')) {
+    return line.substring(line.indexOf('(') + 1, line.indexOf(')'));
+  }
+
+  // Safari & Firefox
+  if (line.includes('@')) {
+    return line.substring(line.indexOf('@') + 1);
+  }
+
+  // Give up
+  return line;
+}