Alerting: Improve API error payload handling (#109956)

* Handle error.data being set to null

* Tidy up code

public/app/features/alerting/unified/utils/misc.test.ts

@@ -196,4 +196,71 @@ describe('stringifyErrorLike', () => {
 
     expect(stringifyErrorLike(error)).toBe('POST /my/url failed with 404: not found');
   });
+
+  it('should prioritize data.message over statusText when both are present', () => {
+    const error = {
+      status: 500,
+      data: { message: 'API error message' },
+      statusText: 'Internal Server Error',
+      config: { url: '/api/test', method: 'GET' },
+    } satisfies FetchError;
+
+    expect(stringifyErrorLike(error)).toBe('GET /api/test failed with 500: API error message');
+  });
+
+  it('should fall back to statusText when data.message is not available', () => {
+    const error = {
+      status: 404,
+      data: { error: 'some other field' },
+      statusText: 'Not Found',
+      config: { url: '/api/test', method: 'GET' },
+    } satisfies FetchError;
+
+    expect(stringifyErrorLike(error)).toBe('Not Found');
+  });
+
+  it('should handle null data safely without crashing', () => {
+    const error = {
+      status: 500,
+      data: null,
+      statusText: 'Internal Server Error',
+      config: { url: '/api/test', method: 'POST' },
+    } satisfies FetchError<null>;
+
+    expect(stringifyErrorLike(error)).toBe('Internal Server Error');
+  });
+
+  it('should handle undefined data safely without crashing', () => {
+    const error = {
+      status: 500,
+      data: undefined,
+      statusText: 'Internal Server Error',
+      config: { url: '/api/test', method: 'PUT' },
+    } satisfies FetchError<undefined>;
+
+    expect(stringifyErrorLike(error)).toBe('Internal Server Error');
+  });
+
+  it('should handle data without message property safely', () => {
+    const error = {
+      status: 400,
+      data: { error: 'validation failed', code: 400 },
+      statusText: 'Bad Request',
+      config: { url: '/api/validate', method: 'POST' },
+    } satisfies FetchError;
+
+    expect(stringifyErrorLike(error)).toBe('Bad Request');
+  });
+
+  it('should prioritize error.message over data.message', () => {
+    const error = {
+      status: 403,
+      message: 'Error message property',
+      data: { message: 'Data message property' },
+      statusText: 'Forbidden',
+      config: { url: '/api/test', method: 'POST' },
+    } satisfies FetchError;
+
+    expect(stringifyErrorLike(error)).toBe('Error message property');
+  });
 });

public/app/features/alerting/unified/utils/misc.ts

@@ -288,6 +288,23 @@ export function isErrorLike(error: unknown): error is Error {
   return Boolean(error && typeof error === 'object' && 'message' in error);
 }
 
+// Small composable guards to safely inspect nested shapes without broad assertions
+function isObject(value: unknown): value is object {
+  return typeof value === 'object' && value !== null;
+}
+
+function hasData(value: unknown): value is { data: unknown } {
+  return isObject(value) && 'data' in value;
+}
+
+function hasMessage(value: unknown): value is { message: string } {
+  if (!isObject(value)) {
+    return false;
+  }
+  const desc = Object.getOwnPropertyDescriptor(value, 'message');
+  return typeof desc?.value === 'string';
+}
+
 export function getErrorCode(error: unknown): string | undefined {
   if (isApiMachineryError(error) && error.data.details) {
     return error.data.details.uid;
@@ -310,8 +327,7 @@ export function isErrorMatchingCode(error: Error | undefined, code: KnownErrorCo
 }
 
 export function stringifyErrorLike(error: unknown): string {
-  const fetchError = isFetchError(error);
-  if (fetchError) {
+  if (isFetchError(error)) {
     if (isApiMachineryError(error)) {
       const message = getErrorMessageFromApiMachineryErrorResponse(error);
       if (message) {
@@ -323,7 +339,8 @@ export function stringifyErrorLike(error: unknown): string {
       return error.message;
     }
 
-    if ('message' in error.data && typeof error.data.message === 'string') {
+    // Runtime check for error.data.message without narrow typing - prioritize over statusText
+    if (hasData(error) && hasMessage(error.data)) {
       const status = getStatusFromError(error);
       const message = getMessageFromError(error);