Fantom Language Support
Rich language support for Fantom in Visual Studio Code, powered by a full Language Server Protocol implementation.
Features
Code Intelligence
- Hover -- type signatures, documentation, and constructor details for types and slots from your code and compiled pods.
- Go to Definition -- jump to the definition of any type, field, or method across your workspace.
- Find References -- locate every usage of a symbol throughout the project.
- Rename Symbol -- rename types, fields, and methods across all files at once.
- Call Hierarchy -- browse incoming and outgoing calls for any method or constructor.
Editing
- Completion -- context-aware autocomplete: pod names in
using statements, dot-completion on receivers, keywords, local variables, and types. Method snippets include parameter placeholders.
- Signature Help -- parameter hints while typing function calls, with the active parameter highlighted.
- Code Actions -- quick fixes including Add missing using, Remove unused using, and Uncomment line.
Navigation
- Document Symbols -- outline and breadcrumb navigation for the current file.
- Workspace Symbol Search --
Ctrl+T fuzzy search across all indexed symbols.
Diagnostics
- Real-time parser errors on every keystroke.
- Compiler diagnostics on save, with automatic cross-file refresh.
- Full-file code formatting with Allman (default) or K&R bracket style.
- Correctly handles triple-quoted multiline strings and list literal indentation.
- Respects your editor tab size and spaces/tabs preference.
Syntax Highlighting
- Semantic token support that goes beyond the bundled TextMate grammar, distinguishing classes, methods, fields, enums, and mixins with modifiers like
declaration, readonly, static, and abstract.
Getting Started
Prerequisites
- Java 11+ on your
PATH.
- Fantom or SkySpark installed locally.
Setup
- Install the extension from the Marketplace.
- Open Settings (
Ctrl+,) and set fantom.home to your Fantom or SkySpark installation directory (e.g. C:\Skyspark\skyspark-4.0.5). If you already have the FAN_HOME environment variable set, you can skip this step.
- Open a
.fan file. The language server starts automatically.
Settings
| Setting |
Default |
Description |
fantom.home |
"" |
Path to the Fantom / SkySpark installation directory. Falls back to the FAN_HOME environment variable. |
fantom.javaOpts |
"-Xmx1024m" |
JVM options for the language server. Increase -Xmx for large codebases. |
fantom.formatting.bracketStyle |
"allman" |
"allman" places braces on a new line. "k&r" places braces on the same line. |
fantom.trace.server |
"off" |
LSP message tracing for debugging: "off", "messages", or "verbose". |
Troubleshooting
The extension does not start
- Verify
fantom.home points to a valid installation containing lib/java/sys.jar.
- Confirm Java is available: run
java -version in a terminal.
- Check the Fantom LSP Launch output channel (
View > Output, then select Fantom LSP Launch) for the exact command that was attempted.
- Wait a few seconds after opening a
.fan file for workspace indexing to finish.
- For large projects, increase memory: set
fantom.javaOpts to "-Xmx2048m" or higher.
- Check the Fantom Language Server output channel for errors.
Diagnostics are missing or stale
- Compiler diagnostics refresh on save. Parser diagnostics update on every keystroke.
- Check that
fantom.formatting.bracketStyle matches your preference.
- The formatter uses your editor's Tab Size and Insert Spaces settings.
High memory usage or crashes
- Increase the heap: set
fantom.javaOpts to "-Xmx2048m".
- Enable
fantom.trace.server at "verbose" to capture logs, then file an issue.
Known Limitations
- Rename and Find References work for types, fields, and methods but not for local variables or method parameters.
License
Free to use. Source code is proprietary. See the LICENSE file included with the extension for details.
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