Add ocamlformat as dev dependency

CONTRIBUTING.md

@@ -18,14 +18,30 @@ below for details.
 
 ### Developing patches
 
+#### Setting up your dev environment
+
+Before starting development on `ppxlib` you should install ppxlib's
+dependencies. If you're doing it for the first time you can create
+a local switch with all the right dependencies installed by running:
+```
+opam switch create ./ --with-test --with-dev-setup
+```
+or if you want to use a pre-existing switch:
+```
+opam install ./ppxlib.opam --deps-only --with-test --with-dev-setup
+```
+
+Note that the `--with-dev-setup` flag is only available from `opam.2.2.0`.
+If you are running an older opam and do not wish to update it, you will have
+to manually install `ocamlformat`.
+
+#### Submitting patches
+
 Before submitting a PR, please run `dune build @install @runtest @fmt`
 on your machine.
 
-In addition to normal dependencies, you'll need to run something like
-`opam install cinaps ocamlformat.0.26.1`, but with the version
-specified in [`.ocamlformat`](.ocamlformat). [cinaps][cinaps] is used
-to keep up-to-date some parts of the code that are auto-generated and
-committed in the repository.
+[cinaps][cinaps] is used to keep up-to-date some parts of the code that are
+auto-generated and committed in the repository.
 
 ### Submitting patches and code review
 

dune-project

@@ -25,7 +25,8 @@
   stdlib-shims
   (ocamlfind :with-test)
   (re (and :with-test (>= 1.9.0)))
-  (cinaps (and :with-test (>= v0.12.1))))
+  (cinaps (and :with-test (>= v0.12.1)))
+  (ocamlformat (and :with-dev-setup (= 0.26.2))))
  (conflicts
   (ocaml-migrate-parsetree (< 2.0.0))
   (ocaml-base-compiler (= 5.1.0~alpha1))

ppxlib.opam

@@ -30,6 +30,7 @@ depends: [
   "ocamlfind" {with-test}
   "re" {with-test & >= "1.9.0"}
   "cinaps" {with-test & >= "v0.12.1"}
+  "ocamlformat" {with-dev-setup & = "0.26.2"}
   "odoc" {with-doc}
 ]
 conflicts: [