Detect when Godot performs hot reload

FileWatcher.gd

class_name FileWatcher extends Node

var last_hash: String = ""

func watch_file(filepath: String, callback: Callable):
	var timer = Timer.new()

	# Function to get file hash
	var get_hash = func():
		var file = FileAccess.open(filepath, FileAccess.READ)
		return file.get_as_text().sha256_text() if file else ""

	# Function to check for changes
	var check_changes = func():
		var current_hash = get_hash.call()
		if current_hash != last_hash and current_hash != "":
			last_hash = current_hash
			callback.call()

	# Setup timer
	add_child(timer)
	timer.wait_time = 1.0
	timer.connect("timeout", check_changes)
	timer.start()
	last_hash = get_hash.call()
	print("Watching file for changes...")

Main.gd

# This script will set up a FileWatcher that with a certain interval checks if the current file has changed.
# When it has changed, on_hot_reload will be called. There you can recreate whatever you want to recreate.
# It's somewhat hacky but it's for making the dev experience nicer so you can disable it for prod builds.

extends Node

var file_watcher = preload("res://FileWatcher.gd").new()

func _ready():
    add_child(file_watcher)
    file_watcher.watch_file("res://Main.gd", on_hot_reload)

func on_hot_reload():
    print("Hot reload happened!")