Extend listener with pre-import events

Context

Born from this discussion on Slack: https://robotframework.slack.com/archives/C015KB1QSDN/p1775116818448659

Robot includes the Listener API:

Robot Framework's listener interface provides a powerful mechanism for getting notifications and for inspecting and modifying data and results during execution.

Recently, I tried to use this API to centrally change library arguments for every library import. In doing so, I found out that the listener API only provides events after the importing is already done. For my use case, I must have an event before the import starts. This applies to both listener v2 and v3.

Goal

Extend the listener API with the following events:

• Before Library import starts
• Before Resource import starts
• Before Variables import starts

Possible design

The current listeners already support the events library_import, resource_import, and variables_import. These events don't need to change.

Add the following events to listener v3:

• start_library_import
• start_resource_import
• start_variables_import

Adding these events may look somethings like this:

Option 1: Reusing importer

class Example:
    ROBOT_LISTENER_API_VERSION = 3

    def start_library_import(self, importer: robot.running.resourcemodel.Import):
        # Does not currently exist

    def library_import(self, library: robot.running.testlibraries.TestLibrary, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

    def start_resource_import(self, importer: robot.running.resourcemodel.Import):
        # Does not currently exist

    def resource_import(self, resource: robot.running.resourcemodel.ResourceFile, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

    def start_variables_import(self, importer: robot.running.resourcemodel.Import):
        # Does not currently exist

    def variables_import(self, attrs, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

Option 2: Reusing parser nodes

class Example:
    ROBOT_LISTENER_API_VERSION = 3

    def start_library_import(self, node: robot.parsing.model.statements.LibraryImport):
        # Does not currently exist

    def library_import(self, library: robot.running.testlibraries.TestLibrary, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

    def start_resource_import(self, node: robot.parsing.model.statements.ResourceImport):
        # Does not currently exist

    def resource_import(self, resource: robot.running.resourcemodel.ResourceFile, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

    def start_variables_import(self, node: robot.parsing.model.statements.VariablesImport):
        # Does not currently exist

    def variables_import(self, attrs, importer: robot.running.resourcemodel.Import):
        # Already exists, is unchanged

Optional additions

Make an alias for the following, already existing, functions:

library_import -> start_library_import resource_import -> start_resource_import variables_import -> start_variables_import

This could be implemented in backwards compatible manner so that we'd add new start/end_library/resource/variables_import hooks. Old library/resource/variables_import hooks could be preserved and called if the matching end_xxx_import methods weren't defined. Thus there would be no need changes to the listener API version. ~Pekka

Acceptance criteria

• The new start_*_import events are called before the relevant file is imported.
• The new start_*_import events receive data on what will be imported.
• The listener can control imports using the new start_*_import events
  • The listener can change the file that will be imported
  • The listener can change the arguments with which the file is imported
  • The listener can change the alias with which the library is imported (only applies to library imports)