paddymahoney / metals

🚧 WIP Language Server for Scala

Metals

This project is an experiment to implement a Language Server for Scala using Scalameta semanticdb and the Scala presentation compiler.

⚠️ This project is very alpha stage. Expect bugs and surprising behavior. Ticket reports and patches are welcome!

Project Goals

This project has the following goals:

• a good UX for the final users, including simple installation and setup
• low memory requirements
• integration with scalameta-based tools, such as Scalafix and Scalafmt

Roadmap

Below is a rough summary of what features have been implemented. Even if some checkbox is marked it does not mean that feature works perfectly. Some of those features are a likely outside the scope of this project, we are still learning and exploring what's possible.

• Compile errors with the Scala Presentation Compiler (textDocument/publishDiagnostics):
  • On build compile
  • As you type
• Integration with the sbt server:
  • Run custom sbt command on save
  • Receive compilation errors (textDocument/publishDiagnostics)
• Linting with Scalafix (textDocument/publishDiagnostics):
  • On build compile
  • As you type
• Refactoring with Scalafix:
  • Quick-fix inspections (textDocument/codeAction)
    • Remove unused imports
  • Rename local symbol (textDocument/rename)
  • Rename global symbol (textDocument/rename)
• Formatting with Scalafmt:
  • Whole file (textDocument/formatting)
  • Selected range (textDocument/rangeFormatting)
  • On save (textDocument/willSaveWaitUntil)
  • As you type (textDocument/onTypeFormatting)
• Code assistance:
  • Auto-complete symbols in scope as you type (textDocument/completions)
  • Auto-complete global symbol and insert missing imports (textDocument/completions)
  • Show parameter list as you type (textDocument/signatureHelp)
  • Show type at position (textDocument/hover)
• Go to definition with SemanticDB (textDocument/definition):
  • Inside the project
  • From project files to Scala dependency source files
  • From project files to Java dependency source files
  • From project dependency to project dependency
• Find references with SemanticDB (textDocument/references):
  • In file (textDocument/documentHighlight)
  • In project
  • In dependencies
• Lookup symbol definition by name:
  • In file (textDocument/documentSymbol)
  • In workspace (workspace/symbol)
• Symbol outline:
  • In file as you type (textDocument/documentSymbol)

Contributing

See the contributing guide.

Team

The current maintainers (people who can merge pull requests) are:

• Alexey Alekhin - @laughedelic
• Gabriele Petronella - @gabro
• Jorge Vicente Cantero - @jvican
• Ólafur Páll Geirsson - @olafurpg
• Shane Delmore - @ShaneDelmore

Acknowledgement

Huge thanks to @dragos for his work on a Scala implementation of the LSP (see: https://github.com/dragos/dragos-vscode-scala). This project helped us get quickly started with LSP. Since then, we have refactored the project's original sources to the point where only a few simple case classes remain.

Related work

• ENSIME: a tool for providing IDE-like features to text editors, that recently added LSP support

Why Metals?

Metals = Meta (from Scalameta) + LS (from Language Server)