🔧 Add a Nix flake

.gitignore

@@ -1,5 +1,9 @@
-# Created by https://www.toptal.com/developers/gitignore/api/ocaml,vim,macos
-# Edit at https://www.toptal.com/developers/gitignore?templates=ocaml,vim,macos
+# Created by https://www.toptal.com/developers/gitignore/api/ocaml,vim,macos,direnv
+# Edit at https://www.toptal.com/developers/gitignore?templates=ocaml,vim,macos,direnv
+
+### direnv ###
+.direnv
+.envrc
 
 ### macOS ###
 # General
@@ -8,7 +12,8 @@
 .LSOverride
 
 # Icon must end with two \r
-Icon
+Icon
+
 
 # Thumbnails
 ._*
@@ -85,5 +90,4 @@ tags
 # Persistent undo
 [._]*.un~
 
-# End of https://www.toptal.com/developers/gitignore/api/ocaml,vim,macos
-n
+# End of https://www.toptal.com/developers/gitignore/api/ocaml,vim,macos,direnv

flake.nix

@@ -0,0 +1,55 @@
+{
+  inputs = {
+    opam-nix.url = "github:tweag/opam-nix";
+    flake-utils.url = "github:numtide/flake-utils";
+    nixpkgs.follows = "opam-nix/nixpkgs";
+  };
+  outputs =
+    {
+      self,
+      flake-utils,
+      opam-nix,
+      nixpkgs,
+    }@inputs:
+    let
+      package = "react_trace";
+    in
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        on = opam-nix.lib.${system};
+        devPackagesQuery = {
+          ocaml-lsp-server = "*";
+          ocamlformat = "*";
+          utop = "*";
+        };
+        query = devPackagesQuery // {
+          ocaml-base-compiler = "*";
+        };
+        scope = on.buildDuneProject { resolveArgs.with-test = true; } package ./. query;
+        overlay = final: prev: {
+          ${package} = prev.${package}.overrideAttrs (_: {
+            # Prevent the ocaml dependencies from leaking into dependent environments
+            doNixSupport = false;
+          });
+        };
+        scope' = scope.overrideScope overlay;
+        main = scope'.${package};
+        devPackages = builtins.attrValues (pkgs.lib.getAttrs (builtins.attrNames devPackagesQuery) scope');
+      in
+      {
+        legacyPackages = scope';
+
+        packages.default = main;
+
+        devShells.default = pkgs.mkShell {
+          inputsFrom = [ main ];
+          buildInputs =
+            devPackages
+            ++ [
+            ];
+        };
+      }
+    );
+}