ci: add nvim.wasm build and nightly release

Add a dedicated nvim.wasm build workflow and
include the resulting WASM artifact in nightly releases.

3 files changed, 187 insertions, 3 deletions

diff --git a/.github/scripts/build_wasm.sh b/.github/scripts/build_wasm.sh
new file mode 100755
index 0000000000..0ca95da381
--- /dev/null
+++ b/.github/scripts/build_wasm.sh
@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+
+# Build nvim.wasm
+
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+OUTDIR="$ROOT/build-wasm"
+
+source "$ROOT/.emsdk/emsdk_env.sh"
+
+mkdir -p "$OUTDIR"
+
+if ! command -v emcc >/dev/null 2>&1; then
+  echo "ERROR: emcc not found"
+  exit 1
+fi
+
+if ! command -v zig >/dev/null 2>&1; then
+  echo "ERROR: zig not found"
+  exit 1
+fi
+
+emcc --version
+zig version
+
+# Install Binaryen if it is not already available.
+BINARYEN_VERSION=132
+BINARYEN_DIR="$ROOT/.binaryen"
+BINARYEN_BIN="$BINARYEN_DIR/binaryen-version_${BINARYEN_VERSION}/bin"
+
+if [ ! -x "$BINARYEN_BIN/wasm-opt" ]; then
+  echo "Installing Binaryen ${BINARYEN_VERSION}..."
+
+  mkdir -p "$BINARYEN_DIR"
+
+  curl -L \
+    "https://github.com/WebAssembly/binaryen/releases/download/version_${BINARYEN_VERSION}/binaryen-version_${BINARYEN_VERSION}-x86_64-linux.tar.gz" \
+    -o /tmp/binaryen.tar.gz
+
+  tar -xf /tmp/binaryen.tar.gz -C "$BINARYEN_DIR"
+fi
+
+export PATH="$BINARYEN_BIN:$PATH"
+
+wasm-opt --version
+
+zig build nvim_bin \
+  -Dtarget=wasm32-emscripten \
+  -Dcpu=generic+atomics+bulk_memory+mutable_globals \
+  -Demscripten-sysroot="$EMSDK/upstream/emscripten/cache/sysroot" \
+  -Doptimize=ReleaseSmall
+
+ZIG_OUT="$ROOT/zig-out/bin"
+
+# Optimize the final WASM artifact with Binaryen.
+wasm-opt -Oz -o "$ZIG_OUT/nvim.wasm" "$ZIG_OUT/nvim.wasm"
+
+required=(
+  nvim.wasm
+  nvim.js
+  nvim.data
+)
+
+missing=()
+
+for name in "${required[@]}"; do
+  if [ -f "$ZIG_OUT/$name" ]; then
+    cp "$ZIG_OUT/$name" "$OUTDIR/$name"
+  else
+    missing+=("$name")
+  fi
+done
+
+if [ "${#missing[@]}" -ne 0 ]; then
+  echo "ERROR: Missing required WASM artifacts: ${missing[*]}"
+  ls -la "$ZIG_OUT" || true
+  exit 2
+fi
+
+echo "build-wasm.sh finished successfully."
diff --git a/.github/workflows/build_wasm.yml b/.github/workflows/build_wasm.yml
new file mode 100644
index 0000000000..14bd499042
--- /dev/null
+++ b/.github/workflows/build_wasm.yml
@@ -0,0 +1,62 @@
+name: nvim.wasm build
+
+on:
+  pull_request:
+    branches:
+      - 'master'
+      - 'release-[0-9]+.[0-9]+'
+    paths:
+      - 'build.zig'
+      - 'build.zig.zon'
+      - '.github/scripts/build_wasm.sh'
+      - '.github/workflows/build_wasm.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build-wasm:
+    name: Build nvim.wasm (Emscripten + Zig)
+    runs-on: ubuntu-24.04
+    timeout-minutes: 90
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+
+      - name: Set up Zig
+        uses: mlugg/setup-zig@d1434d08867e3ee9daa34448df10607b98908d29 # v2.2.1
+        with:
+          version: 0.16.0
+          use-cache: false
+
+      - name: Cache emsdk, Binaryen & build outputs
+        uses: actions/cache@v6.1.0
+        with:
+          path: |
+            ./.emsdk
+            ./.binaryen
+          key: ${{ runner.os }}-wasm-${{ hashFiles('build.zig', 'build.zig.zon', '.github/scripts/build_wasm.sh') }}
+
+      - name: Install system deps
+        run: |
+          sudo apt-get update
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install -y \
+            python3 python3-pip curl unzip
+
+      - name: Install Emscripten SDK
+        run: |
+          set -euo pipefail
+          if [ ! -d ./.emsdk ]; then
+            git clone https://github.com/emscripten-core/emsdk.git ./.emsdk
+            cd ./.emsdk
+            ./emsdk install 6.0.2
+            ./emsdk activate 6.0.2
+            cd -
+          fi
+
+      - name: Build nvim.wasm
+        run: .github/scripts/build_wasm.sh
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 7c646a54e4..5f8e227f8e 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -190,8 +190,49 @@ jobs:
             build/${{ matrix.archive_name }}.msi
           retention-days: 1
 
+  wasm:
+    needs: setup
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+
+      - name: Set up Zig
+        uses: mlugg/setup-zig@d1434d08867e3ee9daa34448df10607b98908d29 # v2.2.1
+        with:
+          version: 0.16.0
+          use-cache: false
+
+      - name: Install system deps
+        run: |
+          sudo apt-get update
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install -y \
+            python3 python3-pip curl unzip
+
+      - name: Install Emscripten SDK
+        run: |
+          set -euo pipefail
+          git clone https://github.com/emscripten-core/emsdk.git ./.emsdk
+          cd ./.emsdk
+          ./emsdk install 6.0.2
+          ./emsdk activate 6.0.2
+          cd -
+
+      - name: Build nvim.wasm
+        run: .github/scripts/build_wasm.sh
+        
+      - name: Upload wasm artifact
+        uses: actions/upload-artifact@v7
+        with:
+          name: nvim-wasm
+          path: build-wasm/*
+          retention-days: 1
+
   publish:
-    needs: [linux, macos, windows]
+    needs: [linux, macos, windows, wasm]
     runs-on: ubuntu-latest
     env:
       GH_REPO: ${{ github.repository }}
@@ -244,6 +285,6 @@ jobs:
         run: |
           envsubst < "$GITHUB_WORKSPACE/.github/workflows/notes.md" > "$RUNNER_TEMP/notes.md"
           if [ "$TAG_NAME" != "nightly" ]; then
-            gh release create stable $PRERELEASE --notes-file "$RUNNER_TEMP/notes.md" --title "$SUBJECT" --target $GITHUB_SHA nvim-macos-x86_64/* nvim-macos-arm64/* nvim-linux-x86_64/* nvim-linux-arm64/* nvim-appimage-x86_64/* nvim-appimage-arm64/* nvim-win-x86_64/* nvim-win-arm64/*
+            gh release create stable $PRERELEASE --notes-file "$RUNNER_TEMP/notes.md" --title "$SUBJECT" --target $GITHUB_SHA nvim-macos-x86_64/* nvim-macos-arm64/* nvim-linux-x86_64/* nvim-linux-arm64/* nvim-appimage-x86_64/* nvim-appimage-arm64/* nvim-win-x86_64/* nvim-win-arm64/* nvim-wasm/*
           fi
-          gh release create $TAG_NAME $PRERELEASE --notes-file "$RUNNER_TEMP/notes.md" --title "$SUBJECT" --target $GITHUB_SHA nvim-macos-x86_64/* nvim-macos-arm64/* nvim-linux-x86_64/* nvim-linux-arm64/* nvim-appimage-x86_64/* nvim-appimage-arm64/* nvim-win-x86_64/* nvim-win-arm64/*
+          gh release create $TAG_NAME $PRERELEASE --notes-file "$RUNNER_TEMP/notes.md" --title "$SUBJECT" --target $GITHUB_SHA nvim-macos-x86_64/* nvim-macos-arm64/* nvim-linux-x86_64/* nvim-linux-arm64/* nvim-appimage-x86_64/* nvim-appimage-arm64/* nvim-win-x86_64/* nvim-win-arm64/* nvim-wasm/*