make on load lambda work

[adhami3310]

import reflex as rx


def index() -> rx.Component:
    return rx.container()


app = rx.App()
app.add_page(index, "/", on_load=lambda: rx.redirect("https://reflex.dev/docs"))

[greptile-apps]

Greptile Overview

Summary

This PR introduces automatic lambda invocation in Reflex's event handling system. The change modifies the `fix_events` function in `reflex/event.py` to detect when an event handler returns a lambda function and automatically call it with no arguments.

The implementation adds a simple check that identifies lambda functions by their __qualname__ attribute being equal to '<lambda>'. When this condition is met, the lambda is immediately invoked with no parameters. This change specifically targets a common user pattern where developers return lambda functions from on_load event handlers expecting them to be automatically executed.

This enhancement integrates seamlessly with Reflex's existing event processing pipeline, sitting within the event normalization logic that already handles various event types and formats. The change maintains backward compatibility since it only affects lambda functions and doesn't alter the behavior of other callable objects or regular functions.

Important Files Changed

Changed Files

Filename	Score	Overview
reflex/event.py	4/5	Adds automatic lambda detection and invocation in the fix_events function

Confidence score: 4/5

• This PR is relatively safe to merge with minimal risk of breaking existing functionality
• Score reflects the targeted nature of the change and the safe lambda detection mechanism using __qualname__
• Pay close attention to the event handling logic in reflex/event.py to ensure lambda detection works as expected

Sequence Diagram

sequenceDiagram
    participant User
    participant "Event System" as ES
    participant "call_script" as CS
    participant Frontend
    participant "Event Handler" as EH

    User->>ES: "Create event with lambda callback"
    ES->>CS: "call_script(js_code, callback_lambda)"
    CS->>CS: "Check if callback is provided"
    alt callback is EventHandler
        CS->>CS: "call_event_handler(callback, _callback_arg_spec)"
        CS->>EH: "Process EventHandler callback"
        EH-->>CS: "Return processed event"
    else callback is Lambda/FunctionType
        CS->>CS: "call_event_fn(callback, _callback_arg_spec)"
        Note over CS: "Lambda now properly handled for on_load"
        CS->>CS: "Parse lambda args and call with result"
        CS-->>CS: "Return lambda result as event"
    else callback is invalid
        CS->>CS: "Raise ValueError"
        CS-->>User: "Error: Invalid callback type"
    end
    CS->>CS: "server_side('_call_script', signature, js_code, callback_kwargs)"
    CS-->>ES: "Return EventSpec"
    ES->>Frontend: "Execute JavaScript code"
    Frontend->>Frontend: "Evaluate JavaScript"
    alt callback exists
        Frontend->>EH: "Send result to callback handler"
        EH->>EH: "Process callback with result"
    end
    Frontend-->>User: "JavaScript execution complete"

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[codspeed-hq]

CodSpeed Performance Report

Merging #5856 will not alter performance

_{Comparing make-on-load-lambda-work (6612a1f) with main (b7230bd)}

Summary

✅ 8 untouched