Simple way to create a ChatMessage from Document content

[julian-risch]

Is your feature request related to a problem? Please describe.
We got the feedback that there is no simple way to create a ChatMessage from Document content with the new ChatMessage implementation.

Describe the solution you'd like
Haystack should support something like: {{document.content|ChatMessage.from_user}}.

Describe alternatives you've considered

Additional context

[anakin87]

I initially thought this was related to the new ChatMessage implementation, so I quickly took a look.

I found that performing this transformation requires the same code with both the current and the new ChatMessage.

from haystack import Document
from haystack.components.converters import OutputAdapter
from haystack.dataclasses import ChatMessage

adapter = OutputAdapter(template="{{ document.content | ChatMessage.from_user }}",
                        output_type=ChatMessage, 
                        unsafe=True, 
                        custom_filters={"ChatMessage.from_user": ChatMessage.from_user})

print(adapter.run(document=Document(content="Test content")))

@mathislucka could you clarify what the original problem was?
(@julian-risch feel free to add information if you know something more)

[mathislucka]

The example is not serializable.

adapter = OutputAdapter(template="{{ document.content | ChatMessage.from_user }}", output_type=ChatMessage, unsafe=True, custom_filters={"ChatMessage.from_user": ChatMessage.from_user})

Gives me: haystack_experimental.dataclasses.chat_message.from_user when serialized.

Why not allow ChatMessage(text="hello", role="user")?