xo-unit: nix: + xo-flatstring dep

pkgs/xo-flatstring.nix

@@ -0,0 +1,37 @@
+{
+  # nixpkgs dependencies
+  stdenv, cmake, catch2, # ... other deps here
+
+  # xo dependencies
+  xo-cmake, xo-indentlog
+
+  # args
+
+  #   attrset for fetching source code.
+  #    { type, owner, repo, ref }
+  #
+  #   e.g. type="github", owner="rconybea", repo="cmake-examples", ref="ex1b"
+  #
+  #   see [[../flake.nix]]
+  #
+  #cmake-examples-ex1-path
+
+  # someconfigurationoption ? false
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-flatstring";
+
+    src = (fetchGit {
+      url = "https://github.com/rconybea/xo-flatstring";
+      version = "1.0";
+      #ref = "ex1";
+      #rev = "c0472c9d7e4d2c53bfb977d3182380832fe96645";
+    });
+
+    cmakeFlags = ["-DXO_CMAKE_CONFIG_EXECUTABLE=${xo-cmake}/bin/xo-cmake-config"];
+    doCheck = true;
+    nativeBuildInputs = [ cmake catch2 ];
+    propagatedBuildInputs = [ xo-indentlog ];
+  })