Add pin-depends for CI to run #27

	name: Build on `trunk`

	on:
	push:
	pull_request:
	schedule:
	# Every weekday, at 5:43 UTC
	- cron: '43 5 * * 1-5'

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- name: Checkout code
	uses: actions/checkout@v2

	- name: Pick up a robust cache prefix
	id: setup
	run: \|
	# Ensure that cache is flushed when trunk is updated
	cache_prefix="$(git ls-remote https://github.com/ocaml/ocaml.git refs/heads/trunk \| cut -f 1)"
	echo "cache_prefix=$cache_prefix" >> "$GITHUB_OUTPUT"
	cat "$GITHUB_OUTPUT"

	- name: Install OCaml compiler
	uses: ocaml/setup-ocaml@v2
	with:
	ocaml-compiler: 'ocaml-variants.5.2.0+trunk'
	dune-cache: true
	cache-prefix: ${{ steps.setup.outputs.cache_prefix }}

	- name: Install ppxlib dependencies
	run: \|
	opam install ./ppxlib.opam --deps-only

	- name: Show configuration
	run: \|
	opam exec -- ocamlc -config
	opam config list
	opam exec -- dune printenv
	opam list

	- name: Build the ppxlib
	run: opam exec -- dune build -p ppxlib

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