Add build / develop environment in Nix

.github/workflows/test-in-nix.yml

@@ -0,0 +1,47 @@
+name: test in Nix
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  tests-in-nix:
+    name: Tests in Nix
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+        ocaml-version:
+          - 4_11
+          - 4_12
+          - 4_13
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Setup Nix
+        uses: cachix/install-nix-action@v15
+        with:
+          nix_path: nixpkgs=channel:nixos-21.11
+          extra_nix_config: |
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+            substituters = https://cache.nixos.org/
+            max-jobs = auto
+            cores = 0
+
+      - name: Build
+        run: |
+          nix-shell --argstr ocamlVersion ${{ matrix.ocaml-version }} --run "dune build"
+
+      - name: Test
+        run: |
+          nix-shell --argstr ocamlVersion ${{ matrix.ocaml-version }} --run "dune runtest"
+
+      - name: Examples
+        run: |
+          nix-shell --argstr ocamlVersion ${{ matrix.ocaml-version }} --run "dune build @examples"

.github/workflows/test.yml

@@ -1,4 +1,4 @@
-name: build
+name: test
 
 on:
   - push

.gitignore

@@ -7,3 +7,5 @@ lib_test/tests_
 *.docdir
 .merlin
 *.install
+
+/result*

README.md

@@ -106,6 +106,12 @@ opam pin add -n httpaf .
 opam install --deps-only httpaf
 ```
 
+If you use [Nix](https://nixos.org/), you can enter `nix-shell`, which contains dev dependencies including ocaml-lsp.
+
+```bash
+nix-shell shell.nix
+```
+
 After this, you may install a development version of the library using the
 install command as usual.
 

default.nix

@@ -0,0 +1,10 @@
+{ pkgs ? import <nixpkgs> {}
+, ocamlVersion ? import ./nix/ocamlDefaultVersion.nix
+, opam2nix ?
+    pkgs.callPackage ./nix/opam2nix.nix {
+      inherit pkgs;
+      ocamlPackagesOverride = pkgs.ocaml-ng."ocamlPackages_${ocamlVersion}";
+
+} }:
+
+pkgs.callPackage ./nix { inherit ocamlVersion opam2nix; }

nix/default.nix

@@ -0,0 +1,36 @@
+{ pkgs, lib, stdenv, ocamlVersion, opam2nix }:
+let
+  inherit (lib) strings;
+  args = {
+    inherit (pkgs.ocaml-ng."ocamlPackages_${ocamlVersion}") ocaml;
+    src =
+      let ignores = pkgs.lib.strings.fileContents ../.gitignore;
+      in pkgs.nix-gitignore.gitignoreSourcePure ignores ../.;
+  };
+
+  opam-selection = opam2nix.build (args // {
+    selection = "${./opam-selection_${ocamlVersion}.nix}";
+  });
+
+  localPackages =
+    let contents = builtins.attrNames (builtins.readDir ../.);
+    in builtins.filter (strings.hasSuffix ".opam") contents;
+
+  # list of dependencies with "with-test" flag manually
+  testPackageNames = [ "alcotest" ];
+  testPackages =
+    builtins.map (name: builtins.getAttr name opam-selection) testPackageNames;
+
+  resolve = opam2nix.resolve (args // {
+    selection = "./nix/opam-selection_${ocamlVersion}.nix";
+  }) (localPackages ++ testPackageNames);
+
+
+in (builtins.listToAttrs (builtins.map (fname:
+  let packageName = strings.removeSuffix ".opam" fname;
+  in {
+    name = packageName;
+    value = builtins.getAttr packageName opam-selection;
+  }) localPackages)) // {
+    inherit resolve opam-selection testPackages;
+  }

nix/ocamlDefaultVersion.nix

@@ -0,0 +1 @@
+"4_13"