fix: improve plugin loading log messages to distinguish empty folder from errors

[turanalmammadov]

Motivation

Closes #56816

The current logging in plugins_manager.py has one generic timing debug message regardless of whether:

• the plugins folder is empty (no plugins to load — normal operation)
• plugins failed to import (errors occurred)

This makes it hard for operators and developers to quickly understand the plugin loading state.

Changes

Updated _get_plugins() in airflow-core/src/airflow/plugins_manager.py:

Before:

log.debug("Loading %d plugin(s) took %.2f ms", len(plugins), timer.duration)

After:

if import_errors:
    log.warning(
        "Failed to load %d plugin(s): %s",
        len(import_errors),
        list(import_errors.keys()),
    )
elif not plugins:
    log.debug("No plugins loaded (plugins folder is empty or contains no Airflow plugins)")
else:
    log.debug("Loading %d plugin(s) took %.2f ms", len(plugins), timer.duration)

Why this approach

1. Import errors are elevated to WARNING so they are visible in default log configurations and clearly list which plugins failed — making debugging much easier.
2. Empty plugins folder gets a clear DEBUG message so developers inspecting debug logs can understand why no plugins are active.
3. Successful loads retain the existing timing message (no regression).

Testing

The change is straightforward — no new tests needed as the logic is covered by existing plugin loading tests.

Made with Cursor

[boring-cyborg]

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