[M7] generated flake.nix moves to build/flake.nix

flake.nix

@@ -10,7 +10,19 @@
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = import nixpkgs { inherit system; };
+        cargoxx = pkgs.gcc15Stdenv.mkDerivation {
+          # Fill rules here
+        };
+        buildCppPackage = attrs: pkgs.gcc15Stdenv.mkDerivation {
+          pname = attrs.pname;
+          version = attrs.version;
+          buildPhase = ''
+            cargoxx build
+          '';
+        };
       in {
+        lib.buildCppPackage = buildCppPackage;
+        package = cargoxx;
         devShell = pkgs.gcc15Stdenv.mkDerivation {
           name = "shell";
           version = "1.0";

src/cli/cmd_build.cpp

@@ -109,7 +109,7 @@ namespace {
 
 auto run_nix_cmake(const fs::path& project_root, const std::vector<std::string>& cmake_args,
                    std::string_view phase) -> util::Result<void> {
-    std::vector<std::string> args{"develop", "--command", "cmake"};
+    std::vector<std::string> args{"develop", "path:./build", "--command", "cmake"};
     args.insert(args.end(), cmake_args.begin(), cmake_args.end());
 
     auto r = exec::run("nix", args, exec::ExecOptions{
@@ -233,7 +233,7 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool release,
             project_root / "build"));
     }
 
-    if (auto r = write_text(project_root / "flake.nix", flake_text); !r) {
+    if (auto r = write_text(project_root / "build" / "flake.nix", flake_text); !r) {
         return std::unexpected(r.error());
     }
     if (auto r = write_text(project_root / "build" / "CMakeLists.txt", cmake_text); !r) {

src/cli/cmd_test.cpp

@@ -19,8 +19,8 @@ auto cmd_test(const fs::path& project_root, bool release,
     const auto build_dir = std::format("build/{}", profile);
 
     auto r = exec::run("nix",
-                       {"develop", "--command", "ctest", "--test-dir", build_dir,
+                       {"develop", "path:./build", "--command", "ctest",
-                        "--output-on-failure"},
+                        "--test-dir", build_dir, "--output-on-failure"},
                        exec::ExecOptions{
                            .cwd = project_root,
                            .env_overrides = {},

src/cli/run.cpp

@@ -115,7 +115,7 @@ auto run(int argc, char** argv) -> int {
             return 1;
         }
         if (build_no_build) {
-            std::cout << "    Generated flake.nix, build/CMakeLists.txt, Cargoxx.lock\n";
+            std::cout << "    Generated build/flake.nix, build/CMakeLists.txt, Cargoxx.lock\n";
         } else {
             std::cout << "    Built\n";
         }

tests/cmd_build.cpp

@@ -64,7 +64,7 @@ TEST_CASE("cmd_build generates files for a no-deps binary project",
     auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
-    REQUIRE(std::filesystem::exists(root / "flake.nix"));
+    REQUIRE(std::filesystem::exists(root / "build" / "flake.nix"));
     REQUIRE(std::filesystem::exists(root / "build" / "CMakeLists.txt"));
     REQUIRE(std::filesystem::exists(root / "Cargoxx.lock"));
 
@@ -73,7 +73,7 @@ TEST_CASE("cmd_build generates files for a no-deps binary project",
     REQUIRE(cmake_text.find("add_executable(hello_bin ../src/main.cpp)") !=
             std::string::npos);
 
-    auto flake_text = read_file(root / "flake.nix");
+    auto flake_text = read_file(root / "build" / "flake.nix");
     REQUIRE(flake_text.find("description = \"hello\";") != std::string::npos);
     REQUIRE(flake_text.find("github:NixOS/nixpkgs/nixos-unstable") != std::string::npos);
 }
@@ -113,7 +113,7 @@ TEST_CASE("cmd_build resolves a manually-seeded dep into find_package + targets"
     REQUIRE(cmake_text.find("find_package(fmt CONFIG REQUIRED)") != std::string::npos);
     REQUIRE(cmake_text.find("fmt::fmt") != std::string::npos);
 
-    auto flake_text = read_file(root / "flake.nix");
+    auto flake_text = read_file(root / "build" / "flake.nix");
     REQUIRE(flake_text.find("pkgs.fmt_10") != std::string::npos);
 }
 
@@ -197,11 +197,11 @@ TEST_CASE("cmd_build is idempotent — second run produces identical files",
 
     REQUIRE(cmd_build(root, true, false, std::nullopt, overlay_path(parent)).has_value());
     auto first_cmake = read_file(root / "build" / "CMakeLists.txt");
-    auto first_flake = read_file(root / "flake.nix");
+    auto first_flake = read_file(root / "build" / "flake.nix");
     auto first_lock = read_file(root / "Cargoxx.lock");
 
     REQUIRE(cmd_build(root, true, false, std::nullopt, overlay_path(parent)).has_value());
     REQUIRE(read_file(root / "build" / "CMakeLists.txt") == first_cmake);
-    REQUIRE(read_file(root / "flake.nix") == first_flake);
+    REQUIRE(read_file(root / "build" / "flake.nix") == first_flake);
     REQUIRE(read_file(root / "Cargoxx.lock") == first_lock);
 }