qgis-core

name	qgis-core
description	Knowledge about the QGIS API, plugin structure, and asynchronous processing with QgsTask.
trigger	when working with PyQGIS, layers, CRS, or QgsTask.

QGIS Core Development

Standardizes interaction with the QGIS API, ensuring a responsive and well-structured plugin.

When to use this skill

• When implementing new tools that interact with the map canvas.
• When handling vector or raster layers.
• When performing heavy operations that require secondary threads.

Degree of Freedom

• Strict: The use of QgsTask for long processes and Core/GUI decoupling are mandatory.

Workflow

1. Architecture: Separate logic into core/ (processing) and gui/ (visualization).
2. Validation: Always verify isValid() on layers before operating.
3. Asynchrony: Wrap processes > 0.5s in a QgsTask.
4. CRS Management: Explicitly handle coordinate transformations.

Instructions and Rules

Golden Rules

• QgsTask: Do not block the UI. Use signals and slots for communication.
• Network/Threads: Avoid threading.Thread (use QgsTask) and synchronous network calls (rules UNSAFE_THREAD and BLOCKING_NETWORK_CALL).
• Boundaries: Use WKT to communicate core logic with the graphical interface.
• Modernization: Avoid legacy QVariant; the analyzer will detect OBSOLETE_VARIANT.
• Injection: Avoid global use of iface; prefer passing objects in constructors.

Plugin Structure

• core/: Business logic agnostic to the UI.
• gui/: Widgets and dialogs dependent on PyQGIS.
• exporters/: Data output modules.

Quality Checklist

• Is UI blocking avoided through QgsTask?
• Is layer integrity validated in every operation?
• Are CRS transformations explicitly defined?
• Is the Core/GUI separation of responsibilities followed?