Language Support for Groovy

A Language Server Protocol implementation for Groovy, powered by Eclipse JDT and groovy-eclipse.

The language server runs as a headless Eclipse/Equinox application, reusing the same Groovy compiler and type inference engine that powers the Eclipse IDE's Groovy support — giving you accurate completions, diagnostics, and navigation backed by a real compiler.

Legal Notice

This project and its VS Code extension are independent community work. They are not affiliated with, endorsed by, or officially released by the Apache Software Foundation.

Features

The following LSP capabilities are supported:

• Completion — context-aware suggestions for methods, properties, variables, and types (triggers: ., , @), with resolve support
• Definition — go-to-definition for classes, methods, and variables (including into external library source JARs)
• Type Definition — navigate to the type declaration of a symbol
• Hover — inline documentation and type information on hover
• References — find all references to a symbol across the workspace
• Implementation — find all implementations of an interface or abstract class
• Rename — safe rename refactoring with prepare support
• Signature Help — parameter hints when calling methods and constructors (triggers: (, ,)
• Document Symbols — outline view of classes, methods, and fields in a file
• Workspace Symbols — search for symbols across the entire workspace
• Code Actions — quick-fix suggestions including remove unused import, delete unused declaration, add missing imports, create unresolved types, implement inherited abstract members, real organize imports, and source.fixAll
• Code Lens — reference counts on types, methods, and fields
• Diagnostics — real-time syntax and compilation error/warning reporting, including unused import and unused declaration detection
• Inlay Hints — inline type annotations for def variables, parameter name hints, closure parameter types, and method return types
• Semantic Highlighting — semantic-aware syntax highlighting with custom typeKeyword token type for class, interface, enum, trait keywords
• Document Highlight — highlights all occurrences of a symbol in the current file
• Formatting — document formatting (full, range, and on-type for }, ;, \n) using a bundled IntelliJ-style default profile, with optional Eclipse formatter XML profile override support
• Folding Ranges — code folding for classes, methods, imports, and region markers
• Type Hierarchy — explore supertypes and subtypes of a class or interface
• Call Hierarchy — explore incoming and outgoing calls for a method
• File Rename — automatic import updates when .groovy or .java files are renamed

VS Code Extension

A bundled VS Code extension provides a seamless editor experience:

• Automatic server lifecycle — the language server starts automatically when a .groovy file is opened or a workspace contains .groovy files
• Red Hat Java integration — the extension works alongside the Language Support for Java™ by Red Hat extension to resolve project classpaths automatically
• Classpath resolution — multi-strategy classpath detection: Java extension API → getProjectSettings fallback → Gradle wrapper fallback (runs gradlew with an init script)
• Go-to-definition into external libraries — navigating to classes from JARs opens a decompiled/source view via the groovy-source:// virtual document provider
• Status bar indicator — shows server state (Waiting for Java, Starting, Importing, Compiling, Ready, Error) with live progress
• Restart command — Groovy: Restart Language Server command to restart the server without reloading the window
• Show Output Channel — Groovy: Show Output Channel command to view the language server log
• Clean workspace on start — Eclipse workspace data is wiped on every launch to avoid stale metadata

Language Configuration

The extension ships a language-configuration.json that enables rich editing support for Groovy files out of the box:

• Comment toggling — Ctrl+/ toggles // line comments; Shift+Alt+A wraps selections in /* */ block comments
• Bracket matching & auto-closing — automatically closes (), [], {}, "", '', and backticks; matching brackets are highlighted
• Doc-comment continuation — pressing Enter inside a /** */ block automatically inserts * on the next line
• Smart indentation — increases indent after {, class, interface, enum, trait, if, for, while, etc.; decreases indent on } or ]
• Folding markers — // region / // endregion (and <editor-fold>) markers create foldable regions in the editor
• Surrounding pairs — selecting text and typing a bracket or quote character wraps the selection

Configuration

Eclipse Formatter XML

By default, the formatter uses the bundled IntelliJ-style profile. You can override it by pointing to an Eclipse formatter XML profile:

{
  "groovy.format.settingsUrl": ".settings/eclipse-formatter.xml"
}

This is the same XML format exported by Eclipse IDE's Java > Code Style > Formatter preferences. Relative paths are resolved from the workspace root.

Prerequisites

• JDK 21 or later
• Language Support for Java™ by Red Hat VS Code extension — required for classpath resolution

Architecture

The language server is built on the Eclipse JDT compiler infrastructure with groovy-eclipse patches that add Groovy support to the Java compiler. This is the same compiler stack used by the Eclipse IDE's Groovy-Eclipse plugin.

Key components:

• Eclipse/Equinox OSGi runtime — the server runs as a headless Equinox application
• groovy-eclipse patched JDT — replaces standard Eclipse JDT with Groovy-aware variants (org.eclipse.jdt.core, org.eclipse.jdt.groovy.core, org.codehaus.groovy)
• LSP4J — provides the LSP protocol binding
• Groovy 5.0 — targets the latest Groovy major version

Build

Requires JDK 21+.

./gradlew build

Build the VS Code extension

# Build the server product and package the .vsix
./gradlew packageVsix

This:

1. Compiles the language server core
2. Assembles the Equinox product (downloads groovy-eclipse bundles, collects plugins)
3. Copies the server into vscode-extension/server/
4. Runs npm install and webpack in the extension directory
5. Packages the .vsix file

The server communicates via standard I/O using the Language Server Protocol.

Provenance & Credits

This project is a clean-room reimplementation of a Groovy language server, built on top of Eclipse JDT and groovy-eclipse. It was started from an initial scaffold in groovy-language-server/groovy-language-server and then rewritten to use the Eclipse compiler infrastructure for accurate type inference, completion, and navigation.

The previous iteration of this project (tomaszrup/groovy-language-server) used a custom Groovy compiler pipeline. This version replaces it entirely with Eclipse JDT + groovy-eclipse for a more robust foundation.

References

• Language Support for Java™ by Red Hat — VS Code extension providing Java language support and classpath resolution via the Java extension API
• Eclipse JDT (Java Development Tools) — the compiler infrastructure and language tooling framework that powers this language server
• Prominic's Groovy Language Server — an earlier Groovy language server that served as inspiration for this project

License

Licensed under the Eclipse Public License - v 2.0.