Notifiers only return a single error rather than all error.

What did you do?

Create a configuration with multiple errors in the same receiver.

What did you expect to see?

All errors.

What did you see instead? Under which circumstances?

❯ ./amtool check-config config/testdata/conf.multi-error.yml
Checking 'config/testdata/conf.multi-error.yml' FAILED: one of url or url_file must be configured

System information

No response

Alertmanager version

Alertmanager configuration file

receivers:
  - name: 'webhook-critical'
    webhook_configs:
      - url: 'http://example.com/api'
        # ERROR 1: send_resolved is a boolean, but a string is provided.
        # The parser hits this and returns an error immediately.
        send_resolved: "yes_please" 

      - url: '' 
        # ERROR 2: The URL is empty (required field). 
        # This error is currently hidden because the process stopped above.
        http_config:
          # ERROR 3: invalid basic_auth (password/password_file are missing).
          basic_auth:
            username: 'admin'

route:
  group_by: ['alertname']
  receiver: 'webhook-critical'

Prometheus version

Prometheus configuration file

Logs

Run amtool check-config against config/testdata/conf.multi-error.yml and trace the receiver notifier validation entry point that stops after the first error. Done means the command reports all applicable validation errors in the receiver, including the invalid send_resolved value, empty URL, and incomplete basic_auth configuration.