Add QML Actions callback system

[Alxiice]

Description

Propose a new system to add callbacks on specific actions.
For now we would add an optional callback to propose to save as template or save as project before saving.
This way this would avoid people saving templates as projects and therefore avoid compatibility node issues.

[gemini-code-assist]

Code Review

This pull request introduces a callback registry system to Meshroom, enabling conditional hooks such as prompting users to save files as standard projects or templates when the MR_ASK_TEMPLATE_BEFORE_SAVING environment variable is set. Key feedback includes resolving a state persistence bug in the save file dialog, fixing a potential QML layout binding loop, removing redundant checks and adding exception handling in the Python-to-QML slots, renaming the decorator to adhere to PEP 8 naming conventions, and centralizing the environment variable definition in meshroom/env.py.

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[gemini-code-assist]

The _saveAsTemplate property is persistent on the saveFileDialog instance. If the dialog was previously used to save a template (setting _saveAsTemplate to true), any subsequent call to prompt() (e.g., from the unsaved changes dialog) will incorrectly inherit this state, causing standard projects to be saved as templates. Reset _saveAsTemplate to false inside prompt() to prevent this.

            _saveAsTemplate = false
            _callback = callback
            open()
        }

[gemini-code-assist]

Using anchors.fill: parent inside a Dialog without an explicit height can cause a binding loop and layout issues, as the dialog's height depends on its content's implicit height, while the content is trying to fill the dialog's height. Instead, anchor only the left and right sides to the parent to respect the dialog's width while letting the height be determined implicitly by the layout's children.

        ColumnLayout {
            anchors.left: parent.left
            anchors.right: parent.right
            spacing: 12

[gemini-code-assist]

The getRegisteredCallback check is redundant because triggerCallback already performs the dictionary lookup and safely returns None if the callback is not registered. Additionally, wrapping the callback execution in a try...except block prevents unhandled exceptions from propagating to QML and potentially crashing the application.

Suggested change

	@Slot(str, result="QVariant")
	def getCallbackResult(self, name):
	"""
	Trigger a registered callback by name (no arguments) and return the result.
	Returns None (undefined in QML) if no callback is registered.
	"""
	cb = getRegisteredCallback(name)
	if cb is None:
	return None
	return triggerCallback(name)
	@Slot(str, result="QVariant")
	def getCallbackResult(self, name):
	"""
	Trigger a registered callback by name (no arguments) and return the result.
	Returns None (undefined in QML) if no callback is registered.
	"""
	try:
	return triggerCallback(name)
	except Exception:
	return None

[gemini-code-assist]

Similar to getCallbackResult, the getRegisteredCallback check is redundant here as well. Wrapping the call in a try...except block ensures that any exceptions raised during callback execution are caught and do not crash the UI.

Suggested change

	@Slot(str, "QVariantList", result="QVariant")
	def triggerCallbackWithArgs(self, name, args):
	"""
	Trigger a registered callback by name with arguments and return the result.
	Args:
	name (str): The callback name.
	args (list): List of arguments to pass to the callback.
	Returns:
	The result of the callback, or None if not registered.
	"""
	cb = getRegisteredCallback(name)
	if cb is None:
	return None
	return triggerCallback(name, *args)
	@Slot(str, "QVariantList", result="QVariant")
	def triggerCallbackWithArgs(self, name, args):
	"""
	Trigger a registered callback by name with arguments and return the result.
	Args:
	name (str): The callback name.
	args (list): List of arguments to pass to the callback.
	Returns:
	The result of the callback, or None if not registered.
	"""
	try:
	return triggerCallback(name, *args)
	except Exception:
	return None

[gemini-code-assist]

Naming the decorator function in ALL_CAPS (REGISTER_CALLBACK) violates PEP 8 naming conventions (which reserves ALL_CAPS for constants) and is inconsistent with the camelCase style used throughout the rest of the codebase. Renaming it to registerCallbackDecorator improves readability and style consistency.

Suggested change

	def REGISTER_CALLBACK(name):
	"""
	Decorator to register a function as a callback.
	Usage:
	@REGISTER_CALLBACK(name="save")
	def my_save_callback(*args, **kwargs):
	...
	"""
	def decorator(func):
	registerCallback(name, func)
	return func
	return decorator
	def registerCallbackDecorator(name):
	"""
	Decorator to register a function as a callback.
	Usage:
	@registerCallbackDecorator(name="save")
	def my_save_callback(*args, **kwargs):
	...
	"""
	def decorator(func):
	registerCallback(name, func)
	return func
	return decorator

[gemini-code-assist]

Update the imports to use the renamed registerCallbackDecorator instead of REGISTER_CALLBACK.

Suggested change

	from meshroom.core.callbacks import (
	registerCallback,
	unregisterCallback,
	getRegisteredCallback,
	triggerCallback,
	clearCallbacks,
	REGISTER_CALLBACK,
	)
	from meshroom.core.callbacks import (
	registerCallback,
	unregisterCallback,
	getRegisteredCallback,
	triggerCallback,
	clearCallbacks,
	registerCallbackDecorator,
	)

[gemini-code-assist]

Update the test case to use the renamed registerCallbackDecorator.

Suggested change

	def test_register_callback_decorator():
	"""Test the REGISTER_CALLBACK decorator."""
	@REGISTER_CALLBACK(name="decorated")
	def my_decorated_cb(x):
	return x * 2
	assert getRegisteredCallback("decorated") is my_decorated_cb
	assert triggerCallback("decorated", 5) == 10
	def test_register_callback_decorator():
	"""Test the registerCallbackDecorator decorator."""
	@registerCallbackDecorator(name="decorated")
	def my_decorated_cb(x):
	return x * 2
	assert getRegisteredCallback("decorated") is my_decorated_cb
	assert triggerCallback("decorated", 5) == 10

[gemini-code-assist]

The environment variable MR_ASK_TEMPLATE_BEFORE_SAVING is accessed directly via os.environ.get. To ensure it is properly documented and listed when running meshroom --env-help, it should be defined in the EnvVar class in meshroom/env.py and accessed through that class.

[codecov]

Codecov Report

❌ Patch coverage is 99.01961% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.45%. Comparing base (37993f4) to head (3a5d54f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
tests/test_callbacks.py	98.43%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3123      +/-   ##
===========================================
+ Coverage    85.33%   85.45%   +0.12%     
===========================================
  Files           73       75       +2     
  Lines        11414    11516     +102     
===========================================
+ Hits          9740     9841     +101     
- Misses        1674     1675       +1     

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[Alxiice]

Seems to work pretty well already.
I would like to clean up the code.
Maybe it's too over-engineered for what we actually want.

Warning

If we don't need it for other things than the save, then maybe do something more specific ?
For example I started a while ago a new custom file browser we could use this instead ?

record-2026-06-05_15.30.12.mp4