add LSIF action

.github/workflows/lsif.yaml

@@ -0,0 +1,30 @@
+name: LSIF
+on: [push, pull_request]
+jobs:
+  build:
+    name: Build and push LSIF data
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: OCaml setup
+        uses: avsm/setup-ocaml@master
+        with:
+          ocaml-version: '4.08.1'
+      - run: opam pin add comby.dev -n .
+      - run: opam depext -yt comby
+      - run: opam install -t . --deps-only
+      - run: opam pin add -y merlin-lsif https://github.com/rvantonder/merlin.git\#lsif
+      - run: opam pin add -y lsif-ocaml https://github.com/rvantonder/lsif-ocaml.git
+      - run: opam exec -- dune build
+#     - name: Setup tmate session
+#       uses: mxschmitt/action-tmate@v1
+      - run: opam exec -- lsif-ocaml-dump
+#     - run: opam exec -- lsif-ocaml -only-type-hovers > dump.lsif
+      - run: opam exec -- lsif-ocaml > dump.lsif
+      - name: Upload LSIF data
+        uses: sourcegraph/lsif-upload-action@master
+        continue-on-error: true
+        with:
+          endpoint: https://sourcegraph.com
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          file: dump.lsif