Remove links-mysql database driver (#1178)

Links currently has two database drivers for MySQL databases, provided by the packages links-mysql and links-mysql8. The former uses the opam package mysql, while the latter uses mysql8.

Unfortunately, the mysql opam package cannot be built on recent versions of Ubuntu anymore and has not been updated in a while. mysql8 is a fork of mysql that does work on more recent versions of Ubuntu, and supports MySQL version 8 (in addition to earlier versions).

Since mysql8 is backwards compatible with earlier versions of MySQL, its functionality subsumes that of mysql. However, since it's a fork of mysql we kept the links-mysql driver around in case the original mysql package gets updated eventually.

This PR is the result of giving up on this hope for the time being: It removes the links-mysql package and associated code within Links.

Since the CI is currently blocked by this, this PR also applies a temporary fix for #1179, by imposing a bound on the version of ppx_sexp_conv

.github/workflows/default.yml

@@ -274,78 +274,6 @@ jobs:
           LINKS_MYSQL8_PORT: ${{ job.services.mysql.ports[3306] }}
         shell: bash
 
-  links-mysql_mysql57:
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-          - ubuntu-18.04
-        ocaml-compiler:
-          - 4.14.1
-          - 5.0.0
-
-    runs-on: ${{ matrix.os }}
-
-    services:
-      mysql:
-        image: mysql:5.7
-        env:
-          MYSQL_USER: links
-          MYSQL_PASSWORD: links
-          MYSQL_ROOT_PASSWORD: links
-          MYSQL_DATABASE: links
-          MYSQL_ROOT_HOST: "%"
-        ports:
-          - 3306:3306
-        options: >-
-          --health-cmd="mysqladmin ping"
-          --health-interval=10s
-          --health-timeout=5s
-          --health-retries=3
-
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@v2
-
-      - name: Install system dependencies
-        run: sudo apt-get install -y libev-dev
-        shell: bash
-
-      - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v2
-        with:
-          ocaml-compiler: ${{ matrix.ocaml-compiler }}
-
-      - run: opam install -y conf-libev
-
-      - name: Install Links dependencies
-        run: >-
-          opam install
-          ./links.opam
-          ./links-mysql.opam
-          --deps-only
-          --ignore-constraints-on=links
-
-      - name: Build Links from source
-        run: |
-          eval $(opam env)
-          make all-ci
-        shell: bash
-
-      - name: Run MySQL5.7 database testsuite
-        run: |
-          eval $(opam env)
-          ./run-database-tests tests/database -d mysql
-          ./run-database-tests tests/relational-lenses -d mysql
-        env:
-          # TODO(dhil): I do not know how to index into the
-          # environments of either service. Until we figure out how to
-          # do it, we will just duplicate information here.
-          LINKS_MYSQL_HOST: 127.0.0.1
-          LINKS_MYSQL_USER: links
-          LINKS_MYSQL_PASSWORD: links
-          LINKS_MYSQL_PORT: ${{ job.services.mysql.ports[3306] }}
-        shell: bash
 
   js-runtime-lint:
     strategy:

CHANGES.md

@@ -1,7 +1,11 @@
 # Unreleased
 
 List of changes since the latest release.
-
+* The package `links-mysql`, based on the `mysql` opam package is no
+  longer supported. Instead, the package `links-mysql8`, based on the
+  `mysql8` package is provided, which also supports version of MySQL
+   prior to 8.
+
 # 0.9.7
 
 This release includes minor bug fixes, improvements, and a breaking

Makefile

@@ -46,9 +46,8 @@ BUILD_DIR:=$(ROOT)/_build
 BUILD=dune build
 MAIN=links
 SOURCES=$(MAIN)
-DB_STABLE=links-postgresql,links-sqlite3,links-mysql
-DB_EXPERIMENTAL=links-mysql8
-DB_SOURCES=$(DB_STABLE),$(DB_EXPERIMENTAL)
+DB_STABLE=links-postgresql,links-sqlite3,links-mysql8
+DB_SOURCES=$(DB_STABLE)
 # Note: this relies on lazy expansion of `SOURCES'.
 COMMON_FLAGS=--only-packages $(SOURCES) --build-dir=$(BUILD_DIR)
 DEV_FLAGS=$(COMMON_FLAGS) --profile=dev