WIT for Zed

WIT adds first-class WebAssembly Interface Types (WIT) support to Zed. The extension combines syntax-aware editing with a native language server for diagnostics, formatting, completion, hover, navigation, references, and safe typo fixes.

The protected v0.1.0 tag identifies the first LSP-only release, but its immutable GitHub Release was deleted. GitHub permanently reserves tag names used by immutable releases, so v0.1.0 cannot be recreated. LSP distribution was restored with v0.1.1 and has since advanced to v0.1.2. This is separate from Zed-extension publication; the extension is not yet published in the Zed registry.

Features

Feature	Implemented behavior
File recognition	.wit files and WIT Markdown code fences
Syntax	Canonical Bytecode Alliance Tree-sitter grammar pinned to an immutable revision
Editing	Highlighting, doc/comments, brackets, indentation, outline, and Vim text objects
Snippets	Package, interface, world, types, functions, imports, exports, and use
Diagnostics	Upstream wit-parser syntax, name/type, and package errors with unsaved-buffer support
Packages	Sibling multi-file packages, direct deps/ files, and package directories
Formatting	Topiary-based document formatting with comment preservation and idempotence checks
Semantic editor features	Scope-aware type completion, resolved hover, go to definition and references, plus deterministic unresolved-type typo fixes

Try it as a development extension

Install Rust via rustup, clone this repository, and build the native language server:

cargo build -p wit-language-server --release --locked
./target/release/wit-language-server --version
mkdir -p .zed
cp .zed/settings.example.json .zed/settings.json

The project-local settings example points Zed at target/release/wit-language-server, relative to the repository worktree. On Windows, change the untracked .zed/settings.json path to target/release/wit-language-server.exe.

The version output includes the package version plus the Git commit captured at build time, for example X.Y.Z+git.<commit>. The same build identity is exposed through LSP serverInfo.version and emitted once through window/logMessage.

In Zed, run zed: install dev extension from the command palette and select the repository root. Open a .wit file, then use the outline panel, completion, navigation, diagnostics, and editor: format to exercise the extension. Inspect zed: open log for startup or build failures.

An existing registry WIT extension is overridden by the development install. Automatic native-server downloads follow package.metadata.zed-wit.runtime-lsp-version in the root manifest. The current pin is 0.1.2, which resolves to the published immutable v0.1.2 LSP release. The LSP package version can advance independently without changing what the extension downloads.

How it works

The root Zed extension is a small Wasm adapter. It uses an explicitly configured language-server binary first, then wit-language-server on the worktree's PATH. Otherwise it downloads the exact native server version paired with the extension, verifies the SHA-256 sidecar, and caches the executable in Zed's extension working directory.

The native server uses upstream wit-parser semantics rather than maintaining a second WIT parser. Sibling .wit files form a package, dependency identities come from WIT declarations rather than directory names, and direct files plus one-level package directories under deps/ resolve in dependency order. Unsaved sibling and dependency edits participate in diagnostics.

The server supports local file URIs and full document synchronization. It does not download package dependencies, discover remote packages, recursively crawl the workspace, or load encoded binary component dependencies. Formatting is document-scoped, refuses syntax-invalid trees, preserves comments, and checks idempotence.

Compatibility

The current compatibility snapshot records Rust 1.99.0, Zed extension API 0.7.0, Tree-sitter ABI 15, and wit-parser 0.260.0. See upstream compatibility for audited revisions and sources.

The native release matrix targets:

• macOS ARM64 and x86_64;
• Linux GNU ARM64 and x86_64;
• Windows x86_64 MSVC.

The grammar recognizes async functions, futures, streams, maps, fixed-length lists, nested packages, versioned paths, and feature annotations. Current Component Model milestones include async in 0.3.0 and maps/external IDs in 0.3.1; fixed-length lists and getter/setter sugar remain gated in the audited spec. Highlighting recognizes syntax independently of semantic feature gates. See validation for qualification evidence and known gaps.

Development

cargo xtask check-no-python
cargo xtask check-dependencies
cargo fmt --all -- --check
cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
cargo test --workspace --all-features --locked
cargo check --workspace --locked
cargo build --target wasm32-wasip2 --locked

After a matching GitHub release exists, cargo xtask test-zed-hosted exercises the real hosted download, cache reuse, and cache-recovery path in an isolated Zed profile.

Read CONTRIBUTING for setup, fixtures, queries, and validation workflows; architecture for component boundaries; and manual testing for real-editor qualification.

AI-Assisted Development

AI tools, including OpenAI's ChatGPT, have assisted with architecture research and planning, implementation and refactoring, debugging, test development, code and security reviews, and documentation and development workflows. Their suggestions are not treated as proof of correctness.

AI-assisted changes are evaluated using checks appropriate to the work, including automated tests, static analysis, builds, and manual Zed qualification where performed. These checks do not guarantee correctness or complete platform coverage; see validation for recorded evidence and limitations.

The human maintainer remains responsible for technical decisions, correctness, security, licensing and attribution, release approval, and ongoing maintenance.

Publication status

The Zed registry already contains a wit extension. Publishing this implementation as its successor requires coordination with the existing maintainer and Zed under the replacement policy. No registry transfer or duplicate entry is assumed.

GitHub release publication is separate from registry publication. The deleted immutable v0.1.0 release remains represented by its protected historical tag, while v0.1.1 is the published immutable recovery LSP-only release. The extension's runtime pin now targets the published immutable v0.1.2 LSP release. Future CD runs explicitly choose lsp or extension scope. LSP and extension versions can advance independently; the extension pins a published LSP version. See publishing for the scope contract and registry succession gate.

Acknowledgements and license

Built on Bytecode Alliance's Tree-sitter WIT grammar, wit-parser, and Topiary. The Bytecode Alliance VS Code extension informed expected editor behavior; its editor-specific implementation was not ported.

Special thanks to Valentine for the original Zed WIT extension, which inspired this project, and for agreeing to let Chiploom take over the wit extension ID in the Zed registry.

Project-owned code is MIT OR Apache-2.0. See LICENSE-MIT, LICENSE-APACHE, and third-party notices. Report vulnerabilities through SECURITY.