nvim-wasm wrapper

This repository is a build wrapper that produces a WebAssembly (WASI) binary of the Neovim submodule without modifying Neovim itself. All WASI-specific shims and patches live outside the submodule.

Try Demo: https://nvim-wasm.pages.dev

nvim-wasm-demo.mp4

Prerequisites

• Lua interpreter (prefer Lua 5.1-compatible like luajit) and curl/tar (toolchain/deps downloads)
• No system installs needed; everything is fetched into .toolchains/

Build

• Build host Lua (codegen):
  • make host-lua
• Build deps (fetch toolchains, build bundled deps):
  • make wasm-deps
• Build wasm (configure + build nvim):
  • make wasm
• Clean:
  • make wasm-clean

Notes

• neovim/ stays untouched; WASI changes live outside the submodule.
• Output build-wasm/bin/nvim is a WASI module (not runnable on the host directly).

Browser demo

• Build wasm: make wasm
• Pick a demo:
  • examples/demo/ — DOM grid (SharedArrayBuffer; requires COOP/COEP)
  • examples/demo-asyncify/ — SAB-free (Asyncify + postMessage; no COOP/COEP)
  • examples/demo-monaco/ — Monaco UI (SharedArrayBuffer; requires COOP/COEP)
  • examples/demo-xterm/ — xterm.js UI (SharedArrayBuffer; requires COOP/COEP)
• Assets:
  • tar -czf examples/<demo>/nvim-runtime.tar.gz -C neovim/.. runtime -C build-wasm usr nvim_version.lua
  • SAB demos: cp build-wasm/bin/nvim examples/<demo>/nvim.wasm
  • SAB-free demo: make demo-asyncify (copies build-wasm/bin/nvim-asyncify.wasm into examples/demo-asyncify/nvim-asyncify.wasm)

Asyncify build

Why

SharedArrayBuffer requires COOP/COEP headers. If you want a browser demo that works without those headers, use the Asyncify build and the SAB-free demo.

Difference vs normal build

• Normal build (build-wasm/bin/nvim): designed for demos that use a SharedArrayBuffer ring for stdin (needs COOP/COEP).
• Asyncify build (build-wasm/bin/nvim-asyncify.wasm): post-processed with Binaryen Asyncify (no Neovim source changes) so wasi_snapshot_preview1.poll_oneoff can suspend, letting the Worker receive postMessage input without SAB.
• Tradeoffs: larger wasm and some overhead from Asyncify.

Build

• Build the base wasm first: make host-lua && make wasm-deps && make wasm
• Generate the Asyncify wasm:
  • make wasm-asyncify