tree-sitter

A VS Code extension that exposes the Tree Sitter API to other extensions.

It can:

1. Load the Tree Sitter WebAssembly module, as well as supported languages.
2. Cache parsed trees.
3. Detect languages.

WIP

This is work-in-progress intended for future use within Dance. A few more polishing touches are needed before it will be ready to publish on the extension store. More importantly, the API is very much subject to change.

Usage

See extension.test.ts for an up-to-date example.

const document = await vscode.workspace.openTextDocument({
  content: `
    pub fn foo() {
      println!("bar");
    }
  `,
  language: "rust",
});

const TreeSitter = await vscode.extensions.getExtension<API>(
  "gregoire.tree-sitter",
).activate()!;

await TreeSitter.withDocumentTree(document, async (tree) => {
  await TreeSitter.withQuery(
    document,
    `(macro_invocation) @macro`,
    (query) => {
      const captures = query.captures(tree.rootNode);
      const macroCapture = captures.find(({ name }) => name === "macro");

      assert.ok(macroCapture);
      assert.strictEqual(macroCapture.node.type, "macro_invocation");
      assert.strictEqual(macroCapture.node.text, 'println!("bar")');
    },
  );
});

Note:

1. Detection of the language of document was done automatically.
2. The Tree Sitter library and Rust parser were both loaded implicitly when calling documentTree().
3. No object had to be manually deleted with .delete(), despite Tree Sitter being a WebAssembly library which requires manual deallocation.
   • It is still possible to manage your objects manually by using documentTree() and query() (instead of their with* counterparts), but you will have to make sure to call .delete() after using them.

Development

Dependencies

Deno and Emscripten must be installed with deno and emcc both available in the PATH.

Setup

Install dependencies with yarn:

$ yarn

A few files must be generated for the build process to continue. Since building these files can be slow and requires internet access, this must be done manually:

$ ./tools.ts --build-wasm --update-text-objects

Building

Run yarn run compile to build the extension, and yarn vsce package to package it for publishing in the store.

Testing

In VS Code, start the watch:test task, then launch "Extension Tests" in the "Run and Debug" menu.

Scope inspection

This extension provides a command named "Inspect Scopes" which displays the current scope in the status bar; hovering the scope will display all its ancestors in a tooltip. This may help write commands that operate on the returned tree or that perform queries.