Try

pkgs/waybar-bluetooth_battery_parse/default.nix

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+import ./waybar-bluetooth_battery_parse.nix

pkgs/waybar-bluetooth_battery_parse/waybar-bluetooth_battery_parse.nix

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+# When you use pkgs.callPackage, parameters here will be filled with packages from Nixpkgs (if there's a match)
+{ lib
+, stdenv
+, fetchFromGitHub
+, cmake
+, ...
+} @ args:
+
+stdenv.mkDerivation rec {
+  # Specify package name and version
+  pname = "waybar-bluetooth_battery_parse";
+  version = "0.0.1";
+
+  # Download source code from GitHub
+  src = fetchFromGitHub ({
+    owner = "Program-Learning";
+    repo = "waybar-bluetooth_battery_parse";
+    # Commit or tag, note that fetchFromGitHub cannot follow a branch!
+    # rev = "0.7.1";
+    # Download git submodules, most packages don't need this
+    fetchSubmodules = false;
+    # Don't know how to calculate the SHA256 here? Comment it out and build the package
+    # Nix will raise an error and show the correct hash
+    sha256 = "sha256-m20M4+3zsH40hTpMJG9cyIjXp0xcCUBS+cCiRVLXFqM=";
+  });
+
+  # Parallel building, drastically speeds up packaging, enabled by default.
+  # You only want to turn this off for one of the rare packages that fails with this.
+  enableParallelBuilding = true;
+  # If you encounter some weird error when packaging CMake-based software, try enabling this
+  # This disables some automatic fixes applied to CMake-based software
+  dontFixCmake = true;
+
+  # Add CMake to the building environment, to generate Makefile with it
+  nativeBuildInputs = [ cmake ];
+
+  # Arguments to CMake that controls functionalities of liboqs
+  cmakeFlags = [
+    "-DBUILD_SHARED_LIBS=ON"
+  ];
+
+  # stdenv.mkDerivation automatically does the rest for you
+}