Wasm Zed extensions#

Gleam can build Zed extensions as WebAssembly components that implement the full zed:extension world (API 0.7.0).

This repository is the compiler. Real extension packages (e.g. Glint) live with the language project, not here.

Installable Glint extension: /home/nandi/code/glint/editors/zed

Author experience#

my_ext/
  gleam.toml          # target = "wasm"
  extension.toml      # languages, grammars, language_servers
  languages/…
  src/extension.gleam

pub type Worktree
pub type Command {
  Command(command: String, args: List(String), env: List(#(String, String)))
}

pub fn language_server_command(
  _id: String,
  worktree: Worktree,
) -> Result(Command, String) {
  // …
}

gleam export zed-extension
# → extension.wasm  (component + zed:api-version)

What the compiler emits#

1. Gleam → MIR → core Wasm for user modules (heap strings, structs, lists, @external(wasm, …) imports).
2. Guest shell for every zed:extension world export:
   • Real language-server-command (PATH which + documented fallback)
   • Defaults for other callbacks (Err("not implemented") / empty results)
   • cabi_realloc bump allocator and post-return no-ops
3. Component packaging via wit-component with vendored WIT (compiler-core/wit/zed_extension/0.7.0/).
4. Custom section zed:api-version: six bytes, big-endian u16 major / minor / patch for 0.7.0.

Zed Install Dev Extension (today)#

Zed always runs cargo build --target wasm32-wasip2 when [lib] kind = "Rust". It does not install a prebuilt Gleam extension.wasm alone. Until that changes, installable extensions still need a thin Rust guest (as in glint/editors/zed).

Grammar keys must match the tree-sitter C symbol (e.g. grammars.gleam → tree_sitter_gleam).

Example package (out of tree)#

Status / roadmap#