Tarun4201 opened a new pull request, #13277:
URL: https://github.com/apache/maven/pull/13277
### Summary & Rationale
Maven contains multiple standalone CLI entry points (e.g. `mvn`, `mvnenc`,
`mvnsh`, `mvnup`). Currently, any extra tools and their dependencies must be
bundled into Maven's shared `${maven.home}/lib/` directory, causing lib
directory bloat and potential version conflicts among third-party CLI tools.
**Maven CLAPP** (Command Line App) resolves this by allowing extra Maven CLI
tools to maintain their private dependencies in an isolated directory structure
under `${maven.home}/lib/clapp/<toolName>/`.
---
### Key Changes Implemented
#### 1. New Entry Point: `MavenClappCling`
- Added `MavenClappCling.java` under `org.apache.maven.cling`.
- - Implements class-loader isolation by scanning
`${maven.home}/lib/clapp/<toolName>/` for `*.jar` files and constructing a
child `URLClassLoader` that inherits from the core Maven class-loader.
- - Reads the tool entry point (e.g. `mainClass`) and delegates invocation
to `main(String[] args, ClassWorld world)`.
- - Falls back to `MavenCling` if no specific CLAPP tool parameters are
provided.
#### 2. Configuration & Class-Realm Updates
- **`m2.conf`**: Added `optionally
${maven.home}/lib/clapp/${maven.clapp.name}/*.jar` so Plexus ClassWorlds
includes tool-specific dependencies dynamically when `maven.clapp.name` is
configured.
- - **`component.xml`**: Updated the distribution assembly descriptor to
include `lib/clapp/` in binary releases.
#### 3. Launcher Script Enhancements
- **`mvn`**:
- - Added support for `--clapp <toolName>` and `--clapp=<toolName>`.
- - Added `_load_clapp_main_class()` function to look up `mainClass` in
`${maven.home}/lib/clapp/<toolName>/clapp.properties`.
- - Passes system properties `-Dmaven.clapp.name` and
`-Dmaven.clapp.mainClass` to the JVM invocation.
#### 4. Documentation & Unit Tests
- **Directory Structure & README**: Created `lib/clapp/README.txt`
explaining the directory layout and `clapp.properties` format.
- - **Unit Testing**: Added `MavenClappClingTest.java` covering jar
discovery, error conditions, and missing configurations.
Fixes #10316.
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