Eclipse, Xtext, english, Software Development

How to get started with Xtext Language Servers and Che

Eclipse Che 5 has support for the Microsoft Language Server Protocol and so has Eclipse Xtext in its new Version 2.11. So let's see how we can bring them both together.

Prerequisites

This tutorial requires some software to be available on your machine. Please install if not already done:

Provide the Xtext Language Server

The first step is to prepare the Xtext Langauge Server. We create a new Xtext Project using the wizard in Eclipse. We deselect the Eclipse plug-in option and choose Gradle as Preferred Build System (option Generic IDE Support is preselected and required). We create a very simple example grammar:

Model:
    greetings+=Greeting*;

Greeting:
'Hello' name=ID ('from' from=[Greeting])? '!';


We will use the gradle application plugin to package our DSL as an executable package. Therefore we edit org.xtext.example.mydsl.ide/build.gradle and add the following code.

apply plugin: 'application'
mainClassName = "org.eclipse.xtext.ide.server.ServerLauncher"
applicationName = 'mydsl-standalone' distributions { main { baseName = 'mydsl' } } distZip { archiveName "mydsl.zip" } distTar { archiveName "mydsl.tar" }


We don't need to code anything to make the DSL Language Server enabled. The real interesting part is the org.eclipse.xtext.ide.server.ServerLauncher main class. This is a class shipped with Xtext that enables Language Server support.

We build the projects with Gradle.

 
./gradlew clean build distZip


Inside the org.xtext.example.mydsl.parent/org.xtext.example.mydsl.ide/build/distributions folder we can now find tar/zip files that we can provide via a webserver so that it later can be pulled from Che.

You can find my prepared version here.

Build a custom "Che with Xtext" plugin

The second step is to add a new Che Plugin that uses our Xtext Lanuage Server to provide editing support for mydslfiles. In order to build a Che extension we need to grap the source code, modify and build it locally.

Get the Che source code

We clone the Che git repository and create a new branch from the latest release tag.

https://github.com/eclipse/che.git
cd che
git checkout -b che-xtext-example 5.1.2

Create the Che plugin

We need to create a plugin that tells Che how to start our Language Server and what the file extension is.

First we create a bunch of folders and pom files.

touch agents/che-core-api-agent/src/main/resources/agents/org.eclipse.che.ls.mydsl.json
touch agents/che-core-api-agent/src/main/resources/agents/scripts/org.eclipse.che.ls.mydsl.script.sh
cd plugins mkdir plugin-mydsl cd plugin-mydsl touch pom.xml mkdir che-plugin-mydsl-lang-server cd che-plugin-mydsl-lang-server touch pom.xml
mkdir -p src/main/java


Here is how the plugin-mydsl/pom.xml looks like:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <artifactId>che-plugin-parent</artifactId>
        <groupId>org.eclipse.che.plugin</groupId>
        <version>5.1.2</version>
        <relativePath>../pom.xml</relativePath>
    </parent>
    <artifactId>che-plugin-mydsl-parent</artifactId>
    <packaging>pom</packaging>
    <name>Che Plugin :: MyDsl (Xtext) :: Parent</name>
    <modules>
        <module>che-plugin-mydsl-lang-server</module>
    </modules>
    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.eclipse.che.core</groupId>
                    <artifactId>che-core-api-dto-maven-plugin</artifactId>
                    <version>${project.version}</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

 
And here is how the plugin-mydsl/che-plugin-mydsl-lang-server/pom.xml looks like:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <artifactId>che-plugin-mydsl-parent</artifactId>
        <groupId>org.eclipse.che.plugin</groupId>
        <version>5.1.2</version>
    </parent>
    <artifactId>che-plugin-mydsl-lang-server</artifactId>
    <name>Che Plugin :: MyDsl (Xtext) :: Extension Server</name>
    <properties>
        <findbugs.failonerror>false</findbugs.failonerror>
    </properties>
    <dependencies>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
        </dependency>
        <dependency>
            <groupId>com.google.inject</groupId>
            <artifactId>guice</artifactId>
        </dependency>
        <dependency>
            <groupId>com.google.inject.extensions</groupId>
            <artifactId>guice-multibindings</artifactId>
        </dependency>
        <dependency>
            <groupId>io.typefox.lsapi</groupId>
            <artifactId>io.typefox.lsapi.services</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-api-core</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-api-languageserver</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-api-languageserver-shared</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-api-project</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-commons-inject</artifactId>
        </dependency>
        <dependency>
            <groupId>org.eclipse.che.core</groupId>
            <artifactId>che-core-commons-lang</artifactId>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
        </dependency>
    </dependencies>
</project>


We register our plugin in the existing plugins/pom.xml.

 <module>plugin-csharp</module>
 <!-- this line is the new entry -->
 <module>plugin-mydsl</module>
 <module>plugin-nodejs</module>


And (including its version) inside the root-pom of Che (/pom.xml).

<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-maven-shared</artifactId>
    <version>${che.version}</version>
</dependency>
<!-- this is the new entry -->
<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-mydsl-lang-server</artifactId>
    <version>${che.version}</version>
</dependency>
<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-nodejs-debugger-ide</artifactId>
    <version>${che.version}</version>
</dependency>


We have to package it into the assembly-wsagent war (assembly/assembly-wsagent-war/pom.xml):

<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-maven-server</artifactId>
</dependency>
<!-- this is the new entry -->
<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-mydsl-lang-server</artifactId>
</dependency>
<dependency>
    <groupId>org.eclipse.che.plugin</groupId>
    <artifactId>che-plugin-nodejs-debugger-server</artifactId>
</dependency>


Implement the code

Now that we've prepared the infrastructure we can start to write the actual plugin code. The easiest way (at least for me) is to import our plugin into eclipse (as maven projects) so that we can write the plugin-code. This should look like this:

Projects after imported in Eclipse

We need to create some Java classes to hook into Che.

The first one is org.eclipse.che.plugin.mydsl.languageserver.MyDslLanguageServerLauncher

package org.eclipse.che.plugin.mydsl.languageserver;

import static java.util.Arrays.asList;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import org.eclipse.che.api.languageserver.exception.LanguageServerException;
import org.eclipse.che.api.languageserver.launcher.LanguageServerLauncherTemplate;
import org.eclipse.che.api.languageserver.shared.model.LanguageDescription;
import org.eclipse.che.api.languageserver.shared.model.impl.LanguageDescriptionImpl;

import com.google.inject.Inject;
import com.google.inject.Singleton;

import io.typefox.lsapi.services.json.JsonBasedLanguageServer;

@Singleton
public class MyDslLanguageServerLauncher extends LanguageServerLauncherTemplate {

    private static final String   LANGUAGE_ID = "mydsl";
    private static final String[] EXTENSIONS  = new String[] {"mydsl"};
    private static final String[] MIME_TYPES  = new String[] {"text/x-mydsl"};
    private static final LanguageDescriptionImpl description;

    private final Path launchScript;

    static {
        description = new LanguageDescriptionImpl();
        description.setFileExtensions(asList(EXTENSIONS));
        description.setLanguageId(LANGUAGE_ID);
        description.setMimeTypes(asList(MIME_TYPES));
    }

    @Inject
    public MyDslLanguageServerLauncher() {
        launchScript = Paths.get(System.getenv("HOME"), "che/ls-mydsl/mydsl/bin/mydsl-standalone");
    }

    @Override
    public LanguageDescription getLanguageDescription() {
        return description;
    }

    @Override
    public boolean isAbleToLaunch() {
        return Files.exists(launchScript);
    }

    protected JsonBasedLanguageServer connectToLanguageServer(Process languageServerProcess) {
        JsonBasedLanguageServer languageServer = new JsonBasedLanguageServer();
        languageServer.connect(languageServerProcess.getInputStream(), languageServerProcess.getOutputStream());
        return languageServer;
    }

    protected Process startLanguageServerProcess(String projectPath) throws LanguageServerException {
        ProcessBuilder processBuilder = new ProcessBuilder(launchScript.toString());
        processBuilder.redirectInput(ProcessBuilder.Redirect.PIPE);
        processBuilder.redirectOutput(ProcessBuilder.Redirect.PIPE);
        try {
            return processBuilder.start();
        } catch (IOException e) {
            throw new LanguageServerException("Can't start JSON language server", e);
        }
    }
}


There are only two interesting things: The LanguageDescription which tells Che what the language id and file extensions etc. are and the startLanguageServerProcess() method that creates a new process for our language server calling a launch script and wires the stdin/stdout of the child process.

We also need to register the launcher class to Che via a new DynaModule.

package org.eclipse.che.plugin.mydsl.inject;

import com.google.inject.AbstractModule;
import com.google.inject.multibindings.Multibinder;

import org.eclipse.che.inject.DynaModule;
import org.eclipse.che.plugin.mydsl.languageserver.MyDslLanguageServerLauncher;
import org.eclipse.che.api.languageserver.launcher.LanguageServerLauncher;

@DynaModule
public class MyDslModule extends AbstractModule {
    @Override
    protected void configure() {
        Multibinder.newSetBinder(binder(), LanguageServerLauncher.class).addBinding().to(MyDslLanguageServerLauncher.class);
    }
}

Prepare the agent

This Che plugin starts our server via a laucher.sh shell script. Therefore we need to add a agent to Che as well. This agent allows us to get the Language Server server part downloaded automatically (side-load). This looks like this:

cd agents/che-core-api-agent/src/main/resources/agents/


Here we create a new JSON org.eclipse.che.ls.mydsl.json file for the MyDsl-Agent

{
"id": "org.eclipse.che.ls.mydsl",
"name": "MyDsl (Xtext) language server",
"description": "MyDsl (Xtext) language server",
"dependencies": [],
"properties": {},
"script" : ""
}

and scripts/org.eclipse.che.ls.mydsl.script.sh that does the download of the server and the unpacking stuff (we basically copy&paste an existing file and adapt it to our needs).

#
# Copyright (c) 2012-2017 Codenvy, S.A.
# All rights reserved. This program and the accompanying materials
# are made available under the terms of the Eclipse Public License v1.0
# which accompanies this distribution, and is available at
# http://www.eclipse.org/legal/epl-v10.html
#
# Contributors:
#   Codenvy, S.A. - initial API and implementation
#

unset PACKAGES
unset SUDO
command -v tar >/dev/null 2>&1 || { PACKAGES=${PACKAGES}" tar"; }
command -v curl >/dev/null 2>&1 || { PACKAGES=${PACKAGES}" curl"; }
test "$(id -u)" = 0 || SUDO="sudo"

AGENT_BINARIES_URI=http://dl.bintray.com/cdietrich/MyDslXtextLanguageServer/mydsl.tar
CHE_DIR=$HOME/che
LS_DIR=${CHE_DIR}/ls-mydsl
LS_LAUNCHER=${LS_DIR}/launch.sh

if [ -f /etc/centos-release ]; then
    FILE="/etc/centos-release"
    LINUX_TYPE=$(cat $FILE | awk '{print $1}')
 elif [ -f /etc/redhat-release ]; then
    FILE="/etc/redhat-release"
    LINUX_TYPE=$(cat $FILE | cut -c 1-8)
 else
    FILE="/etc/os-release"
    LINUX_TYPE=$(cat $FILE | grep ^ID= | tr '[:upper:]' '[:lower:]')
    LINUX_VERSION=$(cat $FILE | grep ^VERSION_ID=)
fi

MACHINE_TYPE=$(uname -m)

mkdir -p ${CHE_DIR}
mkdir -p ${LS_DIR}

########################
### Install packages ###
########################

# Red Hat Enterprise Linux 7
############################
if echo ${LINUX_TYPE} | grep -qi "rhel"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} yum install ${PACKAGES};
    }

# Red Hat Enterprise Linux 6
############################
elif echo ${LINUX_TYPE} | grep -qi "Red Hat"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} yum install ${PACKAGES};
    }

# Ubuntu 14.04 16.04 / Linux Mint 17
####################################
elif echo ${LINUX_TYPE} | grep -qi "ubuntu"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} apt-get update;
        ${SUDO} apt-get -y install ${PACKAGES};
    }


# Debian 8
##########
elif echo ${LINUX_TYPE} | grep -qi "debian"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} apt-get update;
        ${SUDO} apt-get -y install ${PACKAGES};
    }

# Fedora 23
###########
elif echo ${LINUX_TYPE} | grep -qi "fedora"; then
    command -v ps >/dev/null 2>&1 || { PACKAGES=${PACKAGES}" procps-ng"; }
    test "${PACKAGES}" = "" || {
        ${SUDO} dnf -y install ${PACKAGES};
    }


# CentOS 7.1 & Oracle Linux 7.1
###############################
elif echo ${LINUX_TYPE} | grep -qi "centos"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} yum -y install ${PACKAGES};
    }

# openSUSE 13.2
###############
elif echo ${LINUX_TYPE} | grep -qi "opensuse"; then
    test "${PACKAGES}" = "" || {
        ${SUDO} zypper install -y ${PACKAGES};
    }

else
    >&2 echo "Unrecognized Linux Type"
    >&2 cat /etc/os-release
    exit 1
fi


######################
### Install MYDSL LS ###
######################

curl -L -s ${AGENT_BINARIES_URI} > ${LS_DIR}/mydsl.tar && tar xvf ${LS_DIR}/mydsl.tar -C ${LS_DIR}
touch ${LS_LAUNCHER}
chmod +x ${LS_LAUNCHER}
echo "exec ${LS_DIR}/mydsl/bin/mydsl-standalone" >> ${LS_LAUNCHER}


The script looks quite complicated but that's caused by Che's ability to support different linuxes as workspace machines. The relevant part does

  • download the server tar file from the internet
  • unpack it
  • create a launch script

We update scripts/update_agents.sh so that it knows to process ours shell script and JSON

 
updateAgentScript ".." "org.eclipse.che.ls.mydsl"

and run it. Our org.eclipse.che.ls.mydsl.json should be updated with the script now.

Adapt the stacks

To make our agent available we need to create a new Che stack or edit and existing one so that it contains our agent. We edit the debianlsp stack inside ide/che-core-ide-stacks/src/main/resources/stacks.json

 "agents": [
                "org.eclipse.che.terminal",
                "org.eclipse.che.ws-agent",
                "org.eclipse.che.ssh",
                "org.eclipse.che.ls.csharp",
                "org.eclipse.che.ls.json",
                "org.eclipse.che.ls.php",
                "org.eclipse.che.ls.mydsl"
              ],


That's it for coding. So lets build and test it.

Build and run Che

npm install -g bower gulp typings
mvn clean install -P fast
docker run -v /var/run/docker.sock:/var/run/docker.sock -e CHE_DEBUG_SERVER=true -e CHE_ASSEMBLY=/home/dietrich/che-dev/che/assembly/assembly-main/target/eclipse-che-5.1.2/eclipse-che-5.1.2/ codenvy/che-launcher:nightly start

(if you face an EACCES error please refer to this document)

Test it

After the server has started we open a browser and go to http://172.17.0.1:8080 (or the URL Che tells you to go to).

We create a new workspace using the Debian LSP stack and a Blank Project. Once the workspace is started and the project is created we create a new test.mydsl file. We get notified that the Language Server is started and finally can start editing.

Xtext in Che in Action
That's it. You can find the example code here.

 

    
About Christian Dietrich

Christian is committer and co-lead for Eclipse Xtext and has multiple years of experience applying Xtext in customer projects and providing community support in the Xtext forum.