Introduction

KCL provides plugin support through a plugin agent and auxiliary command line tools, and the KCL plugin framework supports different general-purpose languages to develop plugins. The KCL plugin framework currently supports the development of plugins in Python and Go languages.

KCL plugin Git repository: https://github.com/kcl-lang/kcl-plugin

Use Go to Write Plugins

0. Prerequisites

Using the KCL Go plugin requires the presence of Go 1.21+ in your PATH and add the dependency of KCL Go SDK

1. Hello Plugin

Write the following Go code and add the dependency of the hello plugin

package main

import (
    "fmt"

    "kcl-lang.io/kcl-go/pkg/kcl"                   // Import the native API
    _ "kcl-lang.io/kcl-go/pkg/plugin/hello_plugin" // Import the hello plugin
)

func main() {
    yaml := kcl.MustRun("main.k", kcl.WithCode(code)).GetRawYamlResult()
    fmt.Println(yaml)
}

const code = `
import kcl_plugin.hello

name = "kcl"
three = hello.add(1,2)  # hello.add is written by Go
`

In KCL code, the hello plugin can be imported via import kcl_plugin.hello. The output result is

name: kcl
three: 3

2. Plugin Directory Structure

The KCL Go plugin is essentially a simple Go project, mainly containing the Go file api.go for the plugin code, which defines the registration and implementation functions of the plugin.

package hello_plugin

import (
    "kcl-lang.io/kcl-go/pkg/plugin"
)

func init() {
    plugin.RegisterPlugin(plugin.Plugin{
        Name: "hello",
        MethodMap: map[string]plugin.MethodSpec{
            "add": {
                Body: func(args *plugin.MethodArgs) (*plugin.MethodResult, error) {
                    v := args.IntArg(0) + args.IntArg(1)
                    return &plugin.MethodResult{V: v}, nil
                },
            },
        },
    })
}

3. Test Plugin

Write a file called api_test.go to perform unit testing on plugin functions.

package hello_plugin

import (
    "testing"

    "kcl-lang.io/kcl-go/pkg/plugin"
)

func TestPluginAdd(t *testing.T) {
    result_json := plugin.Invoke("kcl_plugin.hello.add", []interface{}{111, 22}, nil)
    if result_json != "133" {
        t.Fatal(result_json)
    }
}

Use Python to Write Plugins

0. Prerequisites

Using the KCL Python plugin requires the presence of Python 3.7+ in your PATH and install the KCL python SDK.

python3 -m pip kcl_lib

1. Hello Plugin

Write the following Python code and add the the plugin named my_plugin.

import kcl_lib.plugin as plugin
import kcl_lib.api as api

plugin.register_plugin("my_plugin", {"add": lambda x, y: x + y})

def main():
    result = api.API().exec_program(
        api.ExecProgram_Args(k_filename_list=["test.k"])
    )
    assert result.yaml_result == "result: 2"

main()

The content of test.k are:

import kcl_plugin.my_plugin

result = my_plugin.add(1, 1)

Use Java to Write Plugins

0. Prerequisites

Using the KCL Java plugin requires the presence of Java 8+ in your PATH and install the KCL Java SDK.

1. Hello Plugin

Write the following Java code and add the the plugin named my_plugin.

package com.kcl;

import com.kcl.api.API;
import com.kcl.api.Spec.ExecProgram_Args;
import com.kcl.api.Spec.ExecProgram_Result;

import java.util.Collections;

public class PluginTest {
    public static void main(String[] mainArgs) throws Exception {
        API.registerPlugin("my_plugin", Collections.singletonMap("add", (args, kwArgs) -> {
            return (int) args[0] + (int) args[1];
        }));
        API api = new API();

        ExecProgram_Result result = api
                .execProgram(ExecProgram_Args.newBuilder().addKFilenameList("test.k").build());
        System.out.println(result.getYamlResult());
    }
}

The content of test.k are:

import kcl_plugin.my_plugin

result = my_plugin.add(1, 1)

Use Rust to Write Plugins

0. Prerequisites

Using the KCL Rust plugin requires the presence of Rust 1.79+ in your PATH and install the KCL Rust SDK.

cargo add anyhow
cargo add kclvm-parser --git https://github.com/kcl-lang/kcl
cargo add kclvm-loader --git https://github.com/kcl-lang/kcl
cargo add kclvm-evaluator --git https://github.com/kcl-lang/kcl
cargo add kclvm-runtime --git https://github.com/kcl-lang/kcl

1. Hello Plugin

Write the following Rust code and add the the plugin named my_plugin.

use anyhow::{anyhow, Result};
use kclvm_evaluator::Evaluator;
use kclvm_loader::{load_packages, LoadPackageOptions};
use kclvm_parser::LoadProgramOptions;
use kclvm_runtime::{Context, IndexMap, PluginFunction, ValueRef};
use std::{cell::RefCell, rc::Rc, sync::Arc};

fn my_plugin_sum(_: &Context, args: &ValueRef, _: &ValueRef) -> Result<ValueRef> {
    let a = args
        .arg_i_int(0, Some(0))
        .ok_or(anyhow!("expect int value for the first param"))?;
    let b = args
        .arg_i_int(1, Some(0))
        .ok_or(anyhow!("expect int value for the second param"))?;
    Ok((a + b).into())
}

fn context_with_plugin() -> Rc<RefCell<Context>> {
    let mut plugin_functions: IndexMap<String, PluginFunction> = Default::default();
    let func = Arc::new(my_plugin_sum);
    plugin_functions.insert("my_plugin.add".to_string(), func);
    let mut ctx = Context::new();
    ctx.plugin_functions = plugin_functions;
    Rc::new(RefCell::new(ctx))
}

fn main() -> Result<()> {
    let src = r#"
import kcl_plugin.my_plugin

sum = my_plugin.add(1, 1)
"#;
    let p = load_packages(&LoadPackageOptions {
        paths: vec!["test.k".to_string()],
        load_opts: Some(LoadProgramOptions {
            load_plugins: true,
            k_code_list: vec![src.to_string()],
            ..Default::default()
        }),
        load_builtin: false,
        ..Default::default()
    })?;
    let evaluator = Evaluator::new_with_runtime_ctx(&p.program, context_with_plugin());
    let result = evaluator.run()?;
    println!("yaml result {}", result.1);
    Ok(())
}

The content of test.k are:

import kcl_plugin.my_plugin

result = my_plugin.add(1, 1)