ballerina-module-strict-library

A Ballerina compiler plugin that enforces library project constraints at compile time. It ensures library packages do not contain executable entrypoints such as public function main(), function init(), service declarations, or listener declarations.

How It Works

When a Ballerina package imports wso2/strict.library in any .bal file, this compiler plugin activates during compilation and scans all source files in the default module. If any entrypoints are found, the plugin reports a compile-time error with diagnostic code STRICT_LIBRARY_101. Multiple violations are reported in a single error message.

Project Structure

Directory	Description
compiler-plugin/	Java implementation of the compiler plugin
compiler-plugin-tests/	Integration tests with sample Ballerina projects
ballerina/	Ballerina marker package that library projects import
build-config/	Checkstyle and code quality configuration

Prerequisites

• JDK 17+
• Ballerina 2201.13.0
• Gradle 8.11.1 (included via wrapper)
• GitHub Packages authentication for Ballerina platform dependencies:
  • packageUser — GitHub username
  • packagePAT — GitHub personal access token

Building from Source

# Build the compiler plugin
./gradlew build

# Run integration tests
./gradlew :strict-library-compiler-plugin-tests:test

# Run code quality checks
./gradlew :strict-library-compiler-plugin:checkstyleMain
./gradlew :strict-library-compiler-plugin:spotbugsMain

Usage

Add the following import to any .bal file in your library project:

import wso2/strict.library as _;

The compiler plugin will automatically validate that your project does not contain:

Construct	Example
Public main function	public function main() { }
Module init function	function init() { }
Service declaration	service / on ep { }
Listener declaration	listener http:Listener ep = new(8080);

If any of these are found, compilation fails with a STRICT_LIBRARY_101 error:

error [STRICT_LIBRARY_101]: library projects must not contain entrypoints. Found: 'public function main' in main.bal

Multiple violations are combined into a single diagnostic, e.g.:

error [STRICT_LIBRARY_101]: library projects must not contain entrypoints. Found: 'public function main' in main.bal, service declaration in svc.bal

Contributing

Contributions are welcome. Before submitting a pull request, ensure all checks pass:

./gradlew build && ./gradlew :strict-library-compiler-plugin-tests:test

This project enforces:

• Checkstyle for code style
• SpotBugs for static bug detection
• TestNG for testing

License

This project is licensed under the Apache License 2.0.