Fly Programming Language — Visual Studio Code Extension

Fly Language logo

Full language support for the Fly programming language in Visual Studio Code.

Features

Editor

Syntax highlighting for .fly and .fly.h files
Semantic highlighting — functions, classes, variables, parameters, and properties are coloured by their semantic role, not just by regex pattern
File icons for dark and light themes
Auto-closing brackets and parentheses
Smart folding — AST-aware folding for function and class bodies, plus manual // #region / // #endregion markers
Built-in snippets — 40+ snippets covering namespaces, functions, classes, interfaces, suites, test blocks, control flow, allocation, error handling, and common patterns (field, arr, getset, list, iface, …)
Onboarding walkthrough — Help → Get Started → "Get Started with Fly" guides you through compiler setup, first program, build/run, and project management

Testing

Fly's test system is intrinsic to the language — tests live inside production code with zero overhead in release builds.

test {} blocks are highlighted as a control-flow keyword. They are written directly inside production functions to observe local state read-only. In release builds they are stripped completely; in test mode they are activated by an active suite.
suite declarations are highlighted as type declarations (keyword + name, like class). Methods ending in Test are test-methods executed automatically; setup / teardown are lifecycle hooks recognised by exact name.
case "label": steps inside test-methods are highlighted and distinguished from switch case by the string-literal label. All steps execute sequentially with isolated error scopes.
Snippets: suite (full scaffold with setup/teardown), testm (test-method with a case), testb (inline test {} block), tcase (single case step).
Hover documentation on suite, test, and case explains all valid contexts, including the distinction between switch-case and test-case.

Language intelligence (via `fly-lsp`)

Hover — documentation for keywords, built-in types, and user-defined symbols (functions, classes, variables)
Completions — context-aware completions from the current scope and all compiled modules
Go to Definition (F12) — jump to the declaration of any symbol
Go to Type Definition — from a variable, jump to its type's class declaration
Go to Implementation — from an interface, list all implementing classes
Find References (Shift+F12) — list all usages across the project
Document Highlights — highlight all occurrences of the symbol under the cursor in the current file
Signature Help — parameter hints popup when typing a function call (( / ,)
Inlay Hints — parameter names shown inline at each call site
Workspace Symbols (Ctrl+T) — fuzzy-search functions and classes across all compiled files
Document Symbols — outline panel and breadcrumbs for the current file
Folding ranges — fold functions, classes and blocks by their real extent rather than by indentation
Semantic tokens — highlighting driven by what a name resolves to, not by the grammar alone

Diagnostics

Live diagnostics — compiler errors and warnings shown inline on save via the $fly problem matcher
Workspace diagnostics — all .fly files in the project are checked at startup, not only open ones; new files are checked automatically

Build, run & debug

Build (Ctrl+Shift+B) — compile the current file; errors appear in the Problems panel
Run (Ctrl+F5) — compile and execute in the integrated terminal
Debug (F5) — compile with --debug and launch under the lldb-dap bundled with the Fly toolchain (bin/lldb-dap, next to fly) — no third-party debugger extension needed
Breakpoints in .fly files are respected by the debugger. Note: the self-host compiler does not emit full DWARF for user programs yet, so source-level stepping is limited.

Projects (`Manifest.fly`)

Manifest support — field completions, hover docs for every manifest field, git-URL links, and CodeLens actions on each dependency
fly init / build / run / test / add / remove / why / lock / clean from the Command Palette and the editor title bar
The manifest is Fly source, not TOML — a class extending fly.meta.Manifest — so it gets the same highlighting and language-server support as the rest of your code

Requirements

Visual Studio Code ^1.82.0
Fly compiler (fly and fly-lsp on PATH, or configured via settings — a release archive ships both in the same bin/, together with lldb-dap used for debugging)

Installation

From the Marketplace

Search for Fly Programming Language in the Extensions panel (Ctrl+Shift+X) or install from the VS Code Marketplace.

From a `.vsix` file

Download the latest .vsix from GitHub Releases, then run:

code --install-extension fly-vscode-extension-<version>.vsix

or drag and drop the file into the Extensions panel.

Building from Source

git clone https://github.com/fly-lang/vscode-extension.git
cd vscode-extension
npm install
npm run compile
npm run package        # produces fly-vscode-extension-<version>.vsix

To run in development mode, open the folder in VS Code and press F5. This compiles the extension and launches an Extension Development Host window.

Settings

Setting	Default	Description
`fly.compilerPath`	`fly`	Path to the Fly compiler binary
`fly.lspPath`	(auto)	Path to `fly-lsp`; auto-discovered next to `fly.compilerPath`
`fly.enableLsp`	`true`	Enable the language server (hover, go-to-definition, references, inlay hints, semantic tokens, workspace symbols, …)
`fly.enableDiagnostics`	`true`	Run compiler on save and show inline diagnostics
`fly.enableWorkspaceDiagnostics`	`true`	Scan all `.fly` files in the workspace at startup
`fly.buildArgs`	(empty)	Extra flags appended to `fly` when running Fly: Build File
`fly.debugBuildArgs`	`--debug`	Compiler flags used by Fly: Debug File
`fly.projectProfile`	(empty = debug)	Profile for the project commands: empty or `release`
`fly.projectForceRebuild`	`false`	Pass `--force` to Fly: Build Project, bypassing the fingerprint cache
`fly.projectBuildArgs`	(empty)	Extra flags appended to `fly build`, e.g. `--target mybin`

Use Fly: Select Compiler from the Command Palette to pick the compiler interactively — the extension auto-discovers all Fly installations and updates fly.lspPath automatically.

The status bar shows two items when a .fly file is active: $(tools) fly X.Y.Z (compiler version, click to change) and $(check) LSP / $(error) LSP (language server connection state).

Commands

Open the Command Palette with Ctrl+Shift+P (Cmd+Shift+P on macOS) and type Fly to filter.

Compiler commands — active on `.fly` files

Command	Shortcut	Description
Fly: Select Compiler	—	Open a quick-pick to choose the active Fly installation. Auto-fills `fly.lspPath` from the same directory.
Fly: Build File	`Ctrl+Shift+B`	Compile the current `.fly` file. Errors appear in the Problems panel via the `$fly` problem matcher.
Fly: Run File	`Ctrl+F5`	Compile and immediately run the current `.fly` file in the integrated terminal. Uses `&&` — the program is not launched if compilation fails.
Fly: Debug File	`F5`	Compile with `--debug` and launch the program under the toolchain's bundled `lldb-dap`. Breakpoints in `.fly` files are respected.

The Debug $(debug-alt), Run $(run), and Build $(play) buttons appear in the editor title bar whenever a .fly file is active.

Project commands — active in a project with a `Manifest.fly`

Every command runs in the directory holding the manifest, which is found by walking up from the active file.

Command	Shortcut	Description
Fly: Init Project	—	Run `fly init` to scaffold `Manifest.fly` and `src/main.fly`.
Fly: Build Project	`Ctrl+Shift+B`	Run `fly build`. Errors appear in the Problems panel. Only changed targets are recompiled.
Fly: Run Project	—	Run `fly run`.
Fly: Test Project	—	Run `fly test` — builds and runs the project's `*Suite.fly` files.
Fly: Add Dependency	—	Interactive: package name, git URL, ref type (`tag` / `branch` / `rev`), and whether it is a dev-dependency; then `fly add`, which also re-locks.
Fly: Remove Dependency	—	Run `fly remove <name>` and re-lock.
Fly: Why Is This Dependency Here?	—	Run `fly why <name>` to explain a package's presence in the graph.
Fly: Select Profile	—	Choose `debug` or `release` for the commands above.
Fly: Clean Project	—	Run `fly clean` for the active profile.
Fly: Lock (Update Lock.fly)	—	Run `fly lock` to re-resolve dependencies and regenerate `Lock.fly`.

The Run $(run-above) and Build $(play) buttons appear in the editor title bar when Manifest.fly is open.

Each dependency in the manifest also carries Why and Remove CodeLens actions, and the dependencies declaration carries Add Dependency.

fly add writes a git dependency: the driver requires exactly one of --tag / --branch / --rev and takes no version, so registry dependencies are added by editing dependencies in the manifest (completions offer the shape) and running Fly: Lock.

Keyboard Shortcuts

Shortcut	Action	Context
`Ctrl+Shift+B` / `Cmd+Shift+B`	Fly: Build File	`.fly` file active
`Ctrl+F5` / `Cmd+F5`	Fly: Run File	`.fly` file active
`F5`	Fly: Debug File	`.fly` file active, not already in debug
`Ctrl+Shift+B` / `Cmd+Shift+B`	Fly: Build Project	`Manifest.fly` active
`F12`	Go to Definition	`.fly` file
`Shift+F12`	Find References	`.fly` file
`Alt+Shift+→`	Expand Selection	`.fly` file
`Ctrl+T` / `Cmd+T`	Workspace Symbols	anywhere

Troubleshooting

"fly-lsp not found" warning in the status bar

The extension cannot find the fly-lsp binary next to the Fly compiler. Options:

Ensure fly-lsp is in the same directory as fly and both are on your PATH.
Set fly.lspPath explicitly in VS Code settings to the full path of the fly-lsp binary.
Run Fly: Select Compiler — the extension will auto-fill fly.lspPath if fly-lsp is a sibling binary.

Compiler not found / status bar shows `$(warning) fly (not found)`

fly is not on PATH or the configured fly.compilerPath is wrong. Run Fly: Select Compiler to search installed Fly versions automatically.

Debug (`F5`) shows "lldb-dap not found"

Debugging uses the lldb-dap binary shipped with the Fly toolchain, expected next to the fly binary. Check that fly.compilerPath points into a full toolchain installation (bin/ containing fly, fly-lsp, lldb-dap), or run Fly: Select Compiler.

Diagnostics appear only for open files

Enable fly.enableWorkspaceDiagnostics (default: true) to scan the entire workspace at startup.

The LSP status bar shows `$(error) LSP` or `$(circle-slash) LSP`

$(circle-slash): LSP is disabled — set fly.enableLsp to true.
$(error): the server crashed or stopped — check the Fly Language Server output channel (View → Output → Fly Language Server) for the error.

Contributing

Running the extension in development mode

git clone https://github.com/fly-lang/vscode-extension.git
cd vscode-extension
npm install

Open the folder in VS Code and press F5. This compiles the TypeScript and launches an Extension Development Host window with the extension loaded from source. Any change to the TypeScript source requires re-running npm run compile (or using npm run watch for incremental rebuilds).

Building the `fly-lsp` language server

There is no separate build step and no CMake target for it: fly-lsp is written in Fly and compiled by the Fly toolchain itself, so it comes out of the ordinary toolchain build. From a checkout of the Fly compiler repository, on the release branch matching your toolchain:

./ci/linux/stage0.sh && ./ci/linux/stage1.sh && ./ci/linux/stage2.sh

On Windows, the same three scripts under ci/windows/ (stage0.ps1, stage1.ps1, stage2.ps1), run with pwsh 7.

The binaries land side by side in build/stage2/bin/ — fly, fly-lsp, fly-registry and the debugger (lldb, lldb-dap) — which is exactly the layout of a release archive. So once fly.compilerPath points at a fly, the extension finds fly-lsp and lldb-dap next to it and fly.lspPath can stay empty.

Reporting issues

Please open an issue at github.com/fly-lang/vscode-extension/issues with:

VS Code version
Extension version (shown in the Extensions panel)
Contents of the Fly Language Server output channel
Steps to reproduce

Releasing

See RELEASING.md for the CI/CD workflow, how to publish a new version to the Marketplace, and the secrets that must be configured in the repository.

License

Apache-2.0

Fly Programming Language

Flylang

Fly Programming Language — Visual Studio Code Extension

Features

Editor

Testing

Language intelligence (via `fly-lsp`)

Diagnostics

Build, run & debug

Projects (`Manifest.fly`)

Requirements

Installation

From the Marketplace

From a `.vsix` file

Building from Source

Settings

Commands

Compiler commands — active on `.fly` files

Project commands — active in a project with a `Manifest.fly`

Keyboard Shortcuts

Troubleshooting

"fly-lsp not found" warning in the status bar

Compiler not found / status bar shows `$(warning) fly (not found)`

Debug (`F5`) shows "lldb-dap not found"

Diagnostics appear only for open files

The LSP status bar shows `$(error) LSP` or `$(circle-slash) LSP`

Contributing

Running the extension in development mode

Building the `fly-lsp` language server

Reporting issues

Releasing

Links

License

Fly Programming Language

Flylang

Fly Programming Language — Visual Studio Code Extension

Features

Editor

Testing

Language intelligence (via fly-lsp)

Diagnostics

Build, run & debug

Projects (Manifest.fly)

Requirements

Installation

From the Marketplace

From a .vsix file

Building from Source

Settings

Commands

Compiler commands — active on .fly files

Project commands — active in a project with a Manifest.fly

Keyboard Shortcuts

Troubleshooting

"fly-lsp not found" warning in the status bar

Compiler not found / status bar shows $(warning) fly (not found)

Debug (F5) shows "lldb-dap not found"

Diagnostics appear only for open files

The LSP status bar shows $(error) LSP or $(circle-slash) LSP

Contributing

Running the extension in development mode

Building the fly-lsp language server

Reporting issues

Releasing

Links

License

Language intelligence (via `fly-lsp`)

Projects (`Manifest.fly`)

From a `.vsix` file

Compiler commands — active on `.fly` files

Project commands — active in a project with a `Manifest.fly`

Compiler not found / status bar shows `$(warning) fly (not found)`

Debug (`F5`) shows "lldb-dap not found"

The LSP status bar shows `$(error) LSP` or `$(circle-slash) LSP`

Building the `fly-lsp` language server