Add a CI that check compatibility with ocaml-lsp (#1614)

Author: voodoos

.github/workflows/ocaml-lsp-compat.yml

@@ -0,0 +1,58 @@
+name: Check ocaml-lsp compat
+
+# Controls when the action will run. Triggers the workflow on push or pull request
+# events but only for the master branch
+on:
+  push:
+    branches: [ master ]
+    paths-ignore:
+      - '**.md'
+      - '**.txt'
+      - '.git*'
+      - 'doc/**'
+      - 'emacs/**'
+      - 'vim/**'
+      - '**/emacs-lint.yml'
+  pull_request:
+    branches: [ master ]
+    paths-ignore:
+      - '**.md'
+      - '**.txt'
+      - '.git*'
+      - 'doc/**'
+      - 'emacs/**'
+      - 'vim/**'
+      - '**/emacs-lint.yml'
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+        ocaml-compiler:
+          - 4.14.x
+    # The type of runner that the job will run on
+    runs-on: ${{ matrix.os }}
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v3
+
+      - name: Set up OCaml ${{ matrix.ocaml-compiler }}
+        uses: ocaml/setup-ocaml@v2
+        with:
+          # Version of the OCaml compiler to initialise
+          ocaml-compiler: ${{ matrix.ocaml-compiler }}
+
+      - name: Check that Merlin and OCaml-LSP are co-installable
+        run: |
+          opam depext conf-jq # opam depext bug
+          opam --cli=2.1 pin --with-version=dev --no-action https://github.com/ocaml/ocaml-lsp.git
+          opam --cli=2.1 pin --with-version=dev --no-action .
+          opam install ocaml-lsp-server --with-test --ignore-constraints-on=merlin-lib
+