Add a shell.nix and instructions how to use it

README.md

@@ -20,6 +20,11 @@ make
 ./musig2test
 ```
 
+## Build in nix-shell
+
+The provided `shell.nix` provides build tools and the right version of
+`libsodium`, so simply using `nix-shell` and `make` is sufficient to build.
+
 # Disclaimer
 This code is work in progress, and has not been audited. Do not use in production. 
 

libsodium.nix

@@ -0,0 +1,14 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.libsodium.overrideAttrs (oldAttrs: {
+    name = "libsodium-1.0.18-musig2";
+    src = pkgs.fetchFromGitHub {
+      owner = "input-output-hk";
+      repo = "libsodium";
+      # branch musig2_compat
+      rev = "7f9f211fcc88d8f0d7a821e5b9041268c392300a";
+      sha256 = "0527x23z1h4ny492jjmyxpwb48hrlbgibin83w1qm0jqvg441xgp";
+    };
+    nativeBuildInputs = [ pkgs.autoreconfHook ];
+    configureFlags = "--enable-static";
+  })

shell.nix

@@ -0,0 +1,7 @@
+{ pkgs ? import <nixpkgs> {}
+, libsodium-musig2 ? import ./libsodium.nix { inherit pkgs; }
+}:
+
+pkgs.mkShell {
+  buildInputs = [pkgs.clang libsodium-musig2];
+}