feat: proc macro for implementing Tool

[cbrit]

• I have looked for existing issues (including closed) about this

Feature Request

Add a proc macro for easily implementing the Tool trait with automatic parameter validation and error handling.

Motivation

Currently, implementing the Tool trait requires a lot of boilerplate code. Obfuscation can be bad, but the macro can act as a shorthand that has all the same info as a function signature, so nothing is really obfuscated except struct creation. Also, by adding this feature in a separate crate it can be optional and not affect core functionality.

Proposal

Add a #[rig_tool] proc macro that:

• Automatically generates a Tool implementation from an async function
• Provides attribute-based configuration for:
  • Tool description
  • Parameter descriptions
    (tool name is function name automatically)

Example usage:

#[rig_tool(
    description = "Perform basic arithmetic operations",
    params(
        x = "First number in the calculation",
        y = "Second number in the calculation",
        operation = "The operation to perform"
    )
)]
async fn calculator(x: i32, y: i32, operation: String) -> Result<i32, rig::tool::ToolError> {
    match operation.as_str() {
        "add" => Ok(x + y),
        "subtract" => Ok(x - y),
        "multiply" => Ok(x * y),
        "divide" => {
             if y == 0 {
                 Err(rig::tool::ToolError::ToolCallError(
                     "Division by zero".into(),
                 ))
             } else {
                 Ok(x / y)
             }
         }
         _ => Err(rig::tool::ToolError::ToolCallError(
             format!("Unknown operation: {}", operation).into(),
         )),
     }
}

Alternatives

Manual Implementation: Continue requiring developers to implement the Tool trait manually.

[linear]

RIG-699 feat: proc macro for implementing Tool