ChatPromptBuilder Fails to JSON Serialize due to ChatMessage class

[lohit8846]

Describe the bug
The new ChatPromptBuilder fails to serialize because of the ChatMessage dataclass. This component takes in a list of ChatMessages in the init method under the template

Error message
TypeError: Object of type ChatMessage is not JSON serializable

Expected behavior
The behavior I expect is that the component gets converted into JSON like this and that we can load with this JSON to create the pipeline back (I'm using a JSON Marshaller)

"components": {
    "ChatPromptBuilder": {
         "init_parameters": {
              "template": [
                   {
                        "content:" "test message"
                        "role": "user",
                        "name": "test"
                        "meta:" {
                            "test": true
                        }
                    }
              ]
         }
     }
}

Additional context
I noticed that ChatPromptBuilder and ChatMessage classes do not have any from dict or to dict functions, so it explains why they fail to serialize. In general, I've seen similar issues reported for DataClasses so I think they should all be serializable

To Reproduce

    messages = [ChatMessage.from_system("You are a helpful assistant giving out valuable information to tourists."), ChatMessage.from_user("Tell me about {{location}}")]`
   chat_prompt_builder = ChatPromptBuilder(template=messages)

[anakin87]

Thanks for reporting this.

Reproducible example

from haystack.components.builders.chat_prompt_builder import ChatPromptBuilder
from haystack.dataclasses import ChatMessage
from haystack import Pipeline

messages = [ChatMessage.from_system("Message")]
chat_prompt_builder = ChatPromptBuilder(template=messages)

pipeline = Pipeline()
pipeline.add_component("builder", chat_prompt_builder)

pipe_str = pipeline.dumps()
new_pipeline = Pipeline().loads(pipe_str)

[CarlosFerLo]

Let me try to solve this!

[CarlosFerLo]

I been working on this for an hour now and I find that the problem here is that the 'component_to_dict' and 'deffault_to_dict' functions do not work recursively on fields that may need serialization, and just lives them as is. This makes serialization fail while we only use straightforward data types that should be serialized and deserialized without any problem.
In order to solve this specific bug we could just create the 'to_dict' and 'from_dict' methods of 'ChatPromptBuilder', but I believe that we could implement a process to serialize and deserialize instances recursively so we do not get this kind of errors again.

[silvanocerza]

@CarlosFerLo go for the simple solution, custom to_dict and from_dict are the way to go.