LSP Support

Xtext supports the generation of language servers that comply to the Language Server Protocol (LSP).

Getting Started in Eclipse

Step 1: Create a new Xtext Project with language server support and Maven as the preferred build system.

Step 2: Implement the Domainmodel language following the Xtext - 15 Minutes Tutorial.

Step 3: Try out the Domainmodel language server in Eclipse based on LSP4E.

1. Configure a content type to the *.dmodel files:
   

2. Create a launch configuration that starts the Domainmodel language server:
   

3. Assign the Domainmodel content type to the Domainmodel language server launcher:
   

4. LSP does not support syntax highlighting (usually it is done on the client side). The following TextMate json file adds syntax highlighting support for the keywords, single-line and multi-line comments of the Domainmodel language:

   {
   "name": "Domainmodel",
   "scopeName": "text.dmodel",
   "fileTypes": [
       "dmodel"
   ],
   "repository": {
       "general": {
           "patterns": [
               {
                   "include": "#linecomment"
               },
               {
                   "include": "#blockcomment"
               },
               {
                   "include": "#keyword"
               }
           ]
       },
       "linecomment": {
           "name": "comment.line.double-dash.dmodel",
           "begin": "(^[ \\t]+)?(?=//)",
           "end": "(?=$)"
       },
       "blockcomment": {
           "name": "comment.block.dmodel",
           "begin": "/\\*(\\*)?(?!/)",
           "end": "\\*/"
       },
       "keyword": {
           "name": "keyword.control.mydsl",
           "match": "\\b(entity|datatype)\\b|!"
   
       }
   },
   "patterns": [
       {
           "include": "#general"
       }
   ],
   "uuid": "8383e49a-fa0d-4bb5-827b-10e8abb294ca"
   }
   

   You may save the content in a file and then add it to the TextMate grammar in Preferences.
   

5. Open a *.dmodel file with the Generic Editor and explore the supported language features like syntax highlighting, content assist, validation, displaying code lenses, quickfixes, formatting, … :
   

Getting Started in IntelliJ IDEA

Step 1: Create a new Xtext Project with language server support and Gradle as the preferred build system.

Step 2: Implement the Domainmodel language following the Xtext - 15 Minutes Tutorial.

Step 3: Try out the Domainmodel language server in IntelliJ IDEA based on the gtache LSP plugin.

1. Generate the Language Server jar file using the gradle clean build command. After the gradle build has been completed successfully, the generated jar file is located in the build folder of the ide project:

   org.example.domainmodel.ide\build\libs\org.example.domainmodel.ide-1.0.0-SNAPSHOT-ls.jar
   

2. Start IntelliJ IDEA and install the LSP plugin via File - Settings... - Plugins - search for 'IntelliJ LSP Support':
   

3. Assign the Domainmodel language server to the *.dmodel extension via File - Settings... - Languages and Frameworks - Language Server Protocol - Server Definitions:
   

4. While opening a Domainmodel file for the first time, the *.dmodel file pattern should be configured to be treated as text files and auto-detect the file type by content:
   

5. After that, whenever a *.dmodel file is opened in IntelliJ IDEA, the Domainmodel Language Server is activated (indicated by the green circle at the bottom right) and provides the supported language features (e.g. code completion) to the user:
   

Further LSP Clients

Feel free to implement further LSP clients to the Domainmodel language server based on Atom, Eclipse Che, Eclipse Theia, Monaco Editor, VS Code, … The currenly supported LSP clients are available in the LSP clients section of https://langserver.org/.

Language Features

Currently, Xtext supports the following LSP language features:

Unit Testing

Automated tests are crucial for the maintainability and the quality of a software product. That is why it is strongly recommended to write unit tests for your language server, too. Xtext provides the org.eclipse.xtext.testing.AbstractLanguageServerTest base class that comes in handy when implementing automated LSP unit tests. The org.eclipse.xtext.ide.tests.server package contains JUnit test cases for almost all supported language features. Feel free to study them to get some inspirations on how to implement automated unit tests for your Xtext-based language server.

Next Chapter: Continuous Integration