Add error-utils helper and tests

src/error-utils.js

@@ -0,0 +1,24 @@
+const ErrorStackParser = require('error-stack-parser')
+
+// Convert an Error's stack into `@actions/core` toolkit AnnotationProperties:
+// https://github.com/actions/toolkit/blob/ef77c9d60bdb03700d7758b0d04b88446e72a896/packages/core/src/core.ts#L36-L71
+function convertErrorToAnnotationProperties(error, title = error.name) {
+  if (!(error instanceof Error)) {
+    throw new TypeError('error must be an instance of Error')
+  }
+
+  const stack = ErrorStackParser.parse(error)
+  const firstFrame = stack && stack.length > 0 ? stack[0] : null
+  if (!firstFrame) {
+    throw new Error('Error stack is empty or unparseable')
+  }
+
+  return {
+    title,
+    file: firstFrame.fileName,
+    startLine: firstFrame.lineNumber,
+    startColumn: firstFrame.columnNumber
+  }
+}
+
+module.exports = { convertErrorToAnnotationProperties }

src/error-utils.test.js

@@ -0,0 +1,38 @@
+const { convertErrorToAnnotationProperties } = require('./error-utils')
+
+describe('error-utils', () => {
+  describe('convertErrorToAnnotationProperties', () => {
+    it('throws a TypeError if the first argument is not an Error instance', () => {
+      expect(() => convertErrorToAnnotationProperties('not an Error')).toThrow(
+        TypeError,
+        'error must be an instance of Error'
+      )
+    })
+
+    it('throws an Error if the first argument is an Error instance without a parseable stack', () => {
+      const error = new Error('Test error')
+      error.stack = ''
+      expect(() => convertErrorToAnnotationProperties(error)).toThrow(Error, 'Error stack is empty or unparseable')
+    })
+
+    it('returns an AnnotationProperties-compatible object', () => {
+      const result = convertErrorToAnnotationProperties(new TypeError('Test error'))
+      expect(result).toEqual({
+        title: 'TypeError',
+        file: __filename,
+        startLine: expect.any(Number),
+        startColumn: expect.any(Number)
+      })
+    })
+
+    it('returns an AnnotationProperties-compatible object with a custom title', () => {
+      const result = convertErrorToAnnotationProperties(new TypeError('Test error'), 'custom title')
+      expect(result).toEqual({
+        title: 'custom title',
+        file: __filename,
+        startLine: expect.any(Number),
+        startColumn: expect.any(Number)
+      })
+    })
+  })
+})