Try adding GHCJS pipeline

Author: maksbotan

.github/workflows/ghcjs.yml

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+name: CI
+
+# Trigger the workflow on push or pull request, but only for the master branch
+on:
+  pull_request:
+  push:
+    branches: [master]
+
+jobs:
+  ghcjs:
+    name: ubuntu-18.04 / ghcjs 8.4
+    runs-on: "ubuntu-18.04"
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: "Setup PATH"
+      run: |
+        echo "PATH=$HOME/.cabal/bin:/opt/ghcjs/8.4/bin:$PATH" >> $GITHUB_ENV
+
+    - name: Install ghcjs and cabal
+      run: |
+        # Default GitHub image dropped ppa:hvr/ghc, so we add it ourselves
+        sudo add-apt-repository ppa:hvr/ghc
+        sudo add-apt-repository ppa:hvr/ghcjs
+        sudo apt-get update -y
+        sudo apt-get install ghcjs-8.4
+        sudo apt-get install cabal-install
+
+        # Override cabal.project with the lightweight GHCJS one
+        cp cabal.ghcjs.project cabal.project
+        cat cabal.project
+
+    - name: Cabal update and freeze
+      run: |
+        cabal v2-update
+        cabal v2-freeze
+
+    - uses: actions/[email protected]
+      name: Cache ~/.cabal/store and dist-newstyle
+      with:
+        path: |
+          ~/.cabal/store
+          dist-newstyle
+        key: ubuntu-18.04-ghcjs8.4-${{ hashFiles('cabal.project.freeze') }}
+        restore-keys: |
+          ubuntu-18.04-ghcjs8.4-
+
+    - name: Install cabal-plan
+      run: |
+        cabal v2-install -w /opt/ghc/8.4.4/bin/ghc --ignore-project cabal-plan --constraint='cabal-plan ^>=0.6.0.0' --constraint='cabal-plan +exe'
+
+    - name: Build
+      run: |
+        cabal v2-build --ghcjs -w /opt/ghcjs/8.4/bin/ghcjs --enable-tests --enable-benchmarks all
+
+    - name: Run tests
+      run: |
+        # cabal v2-test does not work with GHCJS
+        # See: https://github.com/haskell/cabal/issues/6175
+        #
+        # This invokes cabal-plan to figure out test binaries, and invokes them with node.
+        cabal-plan list-bins '*:test:*' | while read -r line; do testpkg=$(echo "$line" | perl -pe 's/:.*//'); testexe=$(echo "$line" | awk '{ print $2 }'); echo "testing $textexe in package $textpkg"; (cd "$(pkgdir $testpkg)" && nodejs "$testexe".jsexe/all.js); done

cabal.ghcjs.project

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+packages:
+  servant-multipart-api
+  servant-multipart-client
+tests: True
+run-tests: True