Validation of (adaptivecard.Attachment).Content is missing

[atc0005]

Overview

While working to implement support for #205 I spent some time reviewing the current codebase. I looked for places to work in the new support without breaking existing logic. During this work, I found issues with the current validation logic.

The validation logic is intended to flow from the adaptivecard.Message entry point to all associated types like so:

• Message
  • Attachments ([]Attachments)
    • Attachment
      • Content (TopLevelCard)
        • Card
          • Body ([]Element)
            • Element
              • many branching paths

Unfortunately, validation breaks down here:

• Message
  • Attachments ([]Attachments)
    • Attachment

go-teams-notify/adaptivecard/adaptivecard.go

Lines 906 to 918 in 9282fe2

	func (a Attachment) Validate() error {
	v := validator.Validator{}
	v.FieldHasSpecificValue(
	a.ContentType,
	"attachment type",
	AttachmentContentType,
	"attachment",
	ErrInvalidType,
	)
	return v.Err()
	}

What should occur is a call to validate Attachment.Content. This in turn should validate all required fields and trigger validation of any associated types downwards or outwards so that everything that should be validated is validated.