Builds your wasm on a macos runner, which has more resources, then uses ubuntu-latest to dockerize it.

github-runner-build-wasm.yaml

name: WASM build and nginxify

on:
  push:
    tags:
      - 'v*'
  workflow_dispatch:
    inputs:
      version:
        description: 'Version number in the format `v1.2.3`'
        required: true
        type: string

env:
  IMAGE_NAME: "username/image-name"

jobs:
  compile-wasm-artifact:
    # has more resources, but costs more minutes, but comes out of usual minutes allowance.
    # default ubuntu-latest for private repos is 2x CPU, 7gb, macos-13 is 4x CPU, 14gb.
    # so we build wasm natively on macos, upload artifact, and download in an ubuntu-latest job
    # to copy into an nginx docker image for linux deployment.
    runs-on: macos-13

    steps:
      - name: Checkout Code
        uses: actions/checkout@v3

      - name: Install Rust
        uses: actions-rs/toolchain@v1
        with:
          toolchain: stable
          override: true

      - name: Install wasm-bindgen-cli
        run: |
          cargo install wasm-bindgen-cli

      - name: Cargo build (for wasm)
        run: |
          rustup target add wasm32-unknown-unknown
          RUSTFLAGS=--cfg=web_sys_unstable_apis TARGET_CC=$(brew --prefix llvm@15)/bin/clang cargo build --release -p spacepit_client --target wasm32-unknown-unknown

      - name: Run wasm-bindgen, prep out dir
        run: |
          wasm-bindgen --no-typescript --target web \
            --out-dir ./out/ \
            --out-name "spacepit" \
            ./target/wasm32-unknown-unknown/release/spacepit_client.wasm
          cp -r client/www/* ./out/
          cp -r assets ./out/

      - name: Archive compiled wasm and assets
        uses: actions/upload-artifact@v4
        with:
          name: wasm-bundle
          path: out

  put-wasm-in-nginx:
    runs-on: ubuntu-latest
    needs: compile-wasm-artifact
    steps:
      - name: Download wasm-bundle artifact
        uses: actions/download-artifact@v4
        with:
          name: wasm-bundle
          
      - name: Prepare Dockerfile
        run: |
          echo '
          FROM nginx:mainline-alpine
          COPY * /usr/share/nginx/html/
          ' > Dockerfile.generated

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.IMAGE_NAME}}
          tags: |
            type=semver,pattern={{version}}
            type=sha,format=long
            latest

      - name: Setup buildx
        uses: docker/setup-buildx-action@v3

      - name: Login to Container Registry
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_PASSWORD }}

      - name: Build and push Docker image
        uses: docker/build-push-action@v6
        with:
          push: true
          context: .
          file: ./Dockerfile.generated
          cache-from: type=gha
          cache-to: type=gha,mode=max
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}