This How-To tutorial explains how to add support for a programming language to Apache NetBeans using the LSP protocol.

What is the Language Server Protocol (LSP)?

How to add support in NetBeans to a programming language using LSP

1. File Type Recognition

See Adding New Language Support.

2. Custom project types

See Adding New Language Support.

3. Semantic Syntax highlighting and braces matching

To add syntax highlighting to your source file, follow the instructions provided in LSP Client demo - (ba)sh language server tutorial.

  1. Download the TextMate json file for your language. A list of Textmate syntaxes is provided here and here but in other places, too. Let's call it my-grammar.json for the purposes of this example. E.g. for Kotlin this would be Kotlin.tmLanguage.json and for Rust rust.tmLanguage.json.

  2. Right-click on Libraries folder of your module project and select Add Module Dependency. Enter "TextMate Lexer" inside Filter and add the module found in the Module list as a dependency to your module.

  3. In the DataObject that you created in the previous chapter, add this annotation:

    @GrammarRegistration(grammar="my-grammar.json", mimeType="text/sh")

    and import it:

    import org.netbeans.modules.textmate.lexer.api.GrammarRegistration;

If you open your source file in NetBeans, via the Windows→Favourites tab, you should be able to see the various parts of the language (e.g. keywords) to be coloured as defined in the TextMate grammar file. Braces matching is also there. Take a look at java/kotlin.editor/src/org/netbeans/modules/kotlin/editor/KtDataObject.java as an example.

4. 5. Code Completion, Formatting and Navigation

To add support for language-specific features like code completion, navigation, etc. you need the help of a Language Protocol Server.  Again, follow the instructions provided in LSP Client demo - (ba)sh language server tutorial. One needs to tell NetBeans to download the LSP binary the first time the user opens a file of the language and to add support for it using the new LSP API provided by NetBeans.

How to add LSP support

Assuming you have download the LSP for your language (as it will be described in the next section), one needs to:

  1. add dependencies to "LSP Client" and "MIME Lookup API" modules to your module
  2. create a new class that implements LanguageServerProvider.

See for example, ShellClient or java/kotlin.editor/src/org/netbeans/modules/kotlin/editor/lsp/KotlinLSPServer:

@MimeRegistration(mimeType="text/x-kotlin", service=LanguageServerProvider.class)
public class KotlinLSPServer implements LanguageServerProvider {
        ServerRestarter restarter = lookup.lookup(ServerRestarter.class);
        Preferences settingsNode = Utils.settings().node(Utils.NODE_LSP);
        settingsNode.addPreferenceChangeListener(new PreferenceChangeListener() {
            @Override
            public void preferenceChange(PreferenceChangeEvent evt) {
                if (evt.getKey() == null || Utils.KEY_LOCATION.equals(evt.getKey())) {
                    restarter.restart();
                    settingsNode.removePreferenceChangeListener(this);
                }
            }
        });
        File server = Utils.getServer();
        if (server == null) {
            return null;
        }
        try {
            ProcessBuilder builder = new ProcessBuilder(new String[] {server.getAbsolutePath()}).directory(server.getParentFile().getParentFile());
            Map<String, String> env = builder.environment();
            File mvnCommand = InstalledFileLocator.getDefault().locate("maven/bin/mvn", null, false);
            if (mvnCommand != null) {
                env.put("PATH", env.get("PATH") + File.pathSeparator + mvnCommand.getParentFile().getAbsolutePath());
            }
      
            Process p = builder.start();
            return LanguageServerDescription.create(p);
        } catch (IOException ex) {
            LOG.log(Level.FINE, null, ex);
            return null;
        }
    }

}

Utils helper class will provide the location of the downloaded LSP file.

public final class Utils {

    public static final String NODE_LSP = "lsp";
    public static final String KEY_LOCATION = "location";

    private Utils() {
    }

    public static Preferences settings() {
        return NbPreferences.forModule(Utils.class);
    } 

    public static File getServer() {
        Preferences settingsNode = Utils.settings().node(Utils.NODE_LSP);
        String location = settingsNode.get(Utils.KEY_LOCATION, "");
        File serverExecutable = new File(new File(location, "bin"), "kotlin-language-server" + (Utilities.isWindows() ? ".bat" : ""));
        if (!serverExecutable.isFile()) {
            return null;
        }
        return serverExecutable;
    }
}

How to add a Hint to download the LSP binary

A list of Language Server implementations and another list of Language Server Implementations. For example, to add support for Kotlin programming language, you need to download kotlin-language-server.

A thread that is executed @OnStart

@OnStart
public class UnconfiguredHint implements Runnable {

    private static final Set<String> KOTLIN_MIME_TYPES = new HashSet<>(Arrays.asList("text/x-kotlin"));

    @Override
    public void run() {
        EditorRegistry.addPropertyChangeListener((PropertyChangeEvent evt) -> updateFocused());
        Utils.settings().addPreferenceChangeListener((PreferenceChangeEvent evt) -> updateFocused());
        updateFocused();
    }

    @Messages("ERR_KotlinSupportMissing=Enhanced Kotlin support is missing, click to install.")
    private synchronized void updateFocused() {
        JTextComponent selectedComponent = EditorRegistry.focusedComponent();
        if (selectedComponent == null) {
            return ;
        }
        Document doc = selectedComponent.getDocument();
        FileObject file = NbEditorUtilities.getFileObject(doc);
        if (file == null || !KOTLIN_MIME_TYPES.contains(FileUtil.getMIMEType(file))) {
            return ;
        }
        List<ErrorDescription> errors = new ArrayList<>();
        File server = Utils.getServer();
        if (server == null) {
            errors.add(ErrorDescriptionFactory.createErrorDescription(Severity.WARNING, Bundle.ERR_KotlinSupportMissing(), Collections.singletonList(new InstallKotlinLSP()), doc, 0));
        }
        HintsController.setErrors(doc, UnconfiguredHint.class.getName(), errors);
    }
    
    private static final class InstallKotlinLSP implements Fix {

        @Override
        public String getText() {
            return "Install Kotlin LSP";
        }

        @Override
        @Messages("DN_KotlinLSP=Kotlin LSP")
        public ChangeInfo implement() throws Exception {
            PluginInstaller.getDefault().install("org.netbeans.libs.kotlin.lsp", null, null, Bundle.DN_KotlinLSP()); // NOI18N
            return null;
        }
    
    }

will display the hint on the editor to download the LSP server. But, modifications are needed on nb/updatecenters.

public class Install extends ModuleInstall {

    @Override
    public void restored() {
        File serverCache = Places.getCacheSubdirectory("kotlin-lsp/server-1.3.3");
        File serverDir = new File(serverCache, "server");
        File executable = new File(new File(serverDir, "bin"), "kotlin-language-server");

        if (!executable.isFile()) {
            File serverZip = InstalledFileLocator.getDefault().locate("kotlin-lsp/server-1.3.3.zip", null, false);
            try (ZipFile zf = new ZipFile(serverZip)) {
                Enumeration<? extends ZipEntry> en = zf.entries();

                while (en.hasMoreElements()) {
                    ZipEntry ze = en.nextElement();
                    if (ze.isDirectory()) {
                        continue;
                    }
                    File target = new File(serverCache, ze.getName());
                    target.getParentFile().mkdirs();
                    try (OutputStream out = new FileOutputStream(target)) {
                        FileUtil.copy(zf.getInputStream(ze), out);
                    }
                }
                if (!Utilities.isWindows()) {
                    executable.setExecutable(true);
                }
                for (ModuleInfo mi : Lookup.getDefault().lookupAll(ModuleInfo.class)) {
                    if ("org.netbeans.modules.kotlin.editor".equals(mi.getCodeNameBase())) {
                        Class<?> utils = mi.getClassLoader().loadClass("org.netbeans.modules.kotlin.editor.Utils");
                        NbPreferences.forModule(utils).node("lsp").put("location", serverDir.getAbsolutePath());
                    }
                }
            } catch (IOException | ClassNotFoundException ex) {
                Exceptions.printStackTrace(ex);
            }
        }
    }

}

More changes are needed. The interested reader can study java/kotlin.editor and nb/updatecenters/extras/libs.kotlin.lsp modules for more information.

Open the source file again and try code completion, formatting, navigation (e.g. jump to definition, peek definition), find all references, symbol search etc.

6. Types and documentation on hover

8. Configuration

See Adding New Language Support.

9. Refactoring

See Adding New Language Support.

10. Error squiggles and apply suggestions from errors

11. Debugging

12. Snippets

13. Build tasks

Plugins supported by LSP

Kotlin plugin is an example of a language support using LSP.

NetBeans Specific Resources

Other resources

  1. Nadeeshaan G. & Nipuna M. (2022), Language Server Protocol and Implementation: Supporting Language-Smart Editing and Programming Tools, APress.
  2. Stalla A. (2021), "Go to Definition in the Language Server Protocol", Strumenta.
  3. Watt D.A. & Brown D. F. (2000), Programming Language Processors in Java, Prentice Hall.
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