[M4] cargoxx build invokes nix+cmake

CHANGELOG.md

@@ -78,6 +78,20 @@ All notable changes to cargoxx will be documented in this file.
   and `[build]` honoring `warnings_as_errors` and `sanitizers`. Source
   paths emitted relative to `build/` (i.e. prefixed with `../`).
   Output is deterministic. `tests/codegen_cmake.cpp` covers 11 cases.
+- `cargoxx build` (without `--no-build`) now drives the full build:
+  `nix develop -c cmake -B build/<profile> -S build -G Ninja
+  -DCMAKE_BUILD_TYPE=<Profile>` then `nix develop -c cmake --build`
+  with optional `--target`, both with `inherit_stdio = true` so the
+  user sees compilation output live. Non-zero cmake exit returns
+  `BuildCmakeFailed`. End-to-end verified: `cargoxx new myapp &&
+  cargoxx build` produces a working `build/debug/myapp` that prints
+  `Hello from myapp!`.
+- Generated `build/CMakeLists.txt` now opts into the experimental
+  `import std;` UUID + `CMAKE_CXX_MODULE_STD ON`, and sets
+  `CMAKE_CXX_EXTENSIONS ON` (deviation from SPEC §8 — required for
+  libc++'s std module to load without `module-file-config-mismatch`
+  on clang 21). Without these the templates from `cargoxx new` fail
+  to compile.
 - `cargoxx.exec`: `ExecResult`, `ExecOptions`, and
   `run(program, args, opts)` — argv-only subprocess wrapper around
   reproc 14.2.4. Captures stdout/stderr (or inherits stdio when

src/cli/cli.cppm

@@ -14,10 +14,12 @@ auto cmd_new(const std::string& name, bool lib_only,
              const std::filesystem::path& parent_dir) -> util::Result<void>;
 
 // Generates flake.nix, build/CMakeLists.txt, and Cargoxx.lock for the project
-// rooted at `project_root`. With `no_build = true`, only generates files; the
+// rooted at `project_root`. With `no_build = true`, only generates files;
-// nix/cmake invocation lands at M4. `overlay_path` lets tests redirect the
+// otherwise also runs `nix develop -c cmake ...` to configure and build.
-// linkdb overlay away from ~/.cache.
+// `target` (when set) is passed through to `cmake --build --target`.
+// `overlay_path` lets tests redirect the linkdb overlay away from ~/.cache.
 auto cmd_build(const std::filesystem::path& project_root, bool no_build, bool release,
+               std::optional<std::string> target = std::nullopt,
                std::optional<std::filesystem::path> overlay_path = std::nullopt)
     -> util::Result<void>;
 

src/cli/cmd_build.cpp

@@ -7,6 +7,7 @@ import cargoxx.layout;
 import cargoxx.linkdb;
 import cargoxx.lockfile;
 import cargoxx.codegen;
+import cargoxx.exec;
 
 namespace cargoxx::cli {
 
@@ -72,7 +73,36 @@ auto synthesize_lockfile(const manifest::Manifest& m,
 
 } // namespace
 
-auto cmd_build(const fs::path& project_root, bool no_build, bool /*release*/,
+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"};
+    args.insert(args.end(), cmake_args.begin(), cmake_args.end());
+
+    auto r = exec::run("nix", args, exec::ExecOptions{
+                                        .cwd = project_root,
+                                        .env_overrides = {},
+                                        .timeout = std::nullopt,
+                                        .inherit_stdio = true,
+                                    });
+    if (!r) {
+        return std::unexpected(r.error());
+    }
+    if (r->exit_code != 0) {
+        return std::unexpected(util::Error{
+            util::ErrorCode::BuildCmakeFailed,
+            std::format("cmake {} failed (exit {})", phase, r->exit_code),
+            "", std::nullopt, std::nullopt,
+        });
+    }
+    return {};
+}
+
+} // namespace
+
+auto cmd_build(const fs::path& project_root, bool no_build, bool release,
+               std::optional<std::string> target,
                std::optional<fs::path> overlay_path) -> util::Result<void> {
     auto manifest_path = project_root / "Cargoxx.toml";
     auto m = manifest::parse(manifest_path);
@@ -124,13 +154,31 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool /*release*/,
         return std::unexpected(r.error());
     }
 
-    if (!no_build) {
+    if (no_build) {
-        return std::unexpected(util::Error{
+        return {};
-            util::ErrorCode::NotImplemented,
+    }
-            "cargoxx build invocation is not implemented in this milestone",
+
-            "rerun with --no-build to generate files only (full build lands at M4)",
+    const std::string profile = release ? "release" : "debug";
-            std::nullopt, std::nullopt,
+    const std::string profile_cap = release ? "Release" : "Debug";
-        });
+    const auto build_dir = std::format("build/{}", profile);
+
+    std::vector<std::string> configure_args{
+        "-B", build_dir,
+        "-S", "build",
+        "-G", "Ninja",
+        std::format("-DCMAKE_BUILD_TYPE={}", profile_cap),
+    };
+    if (auto r = run_nix_cmake(project_root, configure_args, "configure"); !r) {
+        return std::unexpected(r.error());
+    }
+
+    std::vector<std::string> build_args{"--build", build_dir};
+    if (target) {
+        build_args.push_back("--target");
+        build_args.push_back(*target);
+    }
+    if (auto r = run_nix_cmake(project_root, build_args, "build"); !r) {
+        return std::unexpected(r.error());
     }
 
     return {};

src/cli/run.cpp

@@ -23,9 +23,12 @@ auto run(int argc, char** argv) -> int {
         "build", "Generate flake.nix and build/CMakeLists.txt; build with nix+cmake");
     bool build_no_build = false;
     bool build_release = false;
+    std::string build_target;
     build_cmd->add_flag("--no-build", build_no_build,
                         "Generate files only; do not invoke nix/cmake");
     build_cmd->add_flag("--release", build_release, "Build the release profile");
+    build_cmd->add_option("--target", build_target,
+                          "Build a specific target (passed to cmake --build)");
 
     try {
         app.parse(argc, argv);
@@ -52,12 +55,20 @@ auto run(int argc, char** argv) -> int {
     }
 
     if (*build_cmd) {
-        auto r = cmd_build(cwd, build_no_build, build_release);
+        std::optional<std::string> target;
+        if (!build_target.empty()) {
+            target = build_target;
+        }
+        auto r = cmd_build(cwd, build_no_build, build_release, target);
         if (!r) {
             std::cerr << util::format(r.error());
             return 1;
         }
-        std::cout << "    Generated flake.nix, build/CMakeLists.txt, Cargoxx.lock\n";
+        if (build_no_build) {
+            std::cout << "    Generated flake.nix, build/CMakeLists.txt, Cargoxx.lock\n";
+        } else {
+            std::cout << "    Built\n";
+        }
         return 0;
     }
 

src/codegen/cmake.cpp

@@ -59,6 +59,13 @@ auto link_block(std::string_view target_name, std::string_view visibility,
 auto emit_header(const manifest::Manifest& m) -> std::string {
     return std::format(
         "cmake_minimum_required(VERSION 3.30)\n"
+        "\n"
+        "# Opt into experimental C++ modules dyndep + `import std;` support.\n"
+        "# Required until CMake declares these stable.\n"
+        "set(CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP 1)\n"
+        "set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD \"d0edc3af-4c50-42ea-a356-e2862fe7a444\")\n"
+        "set(CMAKE_CXX_MODULE_STD ON)\n"
+        "\n"
         "project({} LANGUAGES CXX)\n"
         "\n"
         "# Generated by cargoxx — do not edit.\n"
@@ -67,7 +74,8 @@ auto emit_header(const manifest::Manifest& m) -> std::string {
         "# ----- toolchain configuration -----\n"
         "set(CMAKE_CXX_STANDARD {})\n"
         "set(CMAKE_CXX_STANDARD_REQUIRED ON)\n"
-        "set(CMAKE_CXX_EXTENSIONS OFF)\n"
+        "# EXTENSIONS=ON for libc++ std-module compatibility (clang 21).\n"
+        "set(CMAKE_CXX_EXTENSIONS ON)\n"
         "set(CMAKE_CXX_SCAN_FOR_MODULES ON)\n"
         "set(CMAKE_EXPORT_COMPILE_COMMANDS ON)\n",
         m.package.name, edition_to_int(m.package.edition));

tests/cmd_build.cpp

@@ -51,7 +51,7 @@ TEST_CASE("cmd_build generates files for a no-deps binary project",
     REQUIRE(cmd_new("hello", false, parent).has_value());
     auto root = parent / "hello";
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
     REQUIRE(std::filesystem::exists(root / "flake.nix"));
@@ -73,7 +73,7 @@ TEST_CASE("cmd_build generates files for a library project", "[cli][build]") {
     REQUIRE(cmd_new("widget", true, parent).has_value());
     auto root = parent / "widget";
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
     auto cmake_text = read_file(root / "build" / "CMakeLists.txt");
@@ -89,7 +89,7 @@ TEST_CASE("cmd_build resolves a curated dep into find_package + targets",
     auto root = parent / "app";
     add_dep(root, "fmt", "10.2.0");
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
     auto cmake_text = read_file(root / "build" / "CMakeLists.txt");
@@ -106,7 +106,7 @@ TEST_CASE("cmd_build resolves a componentized dep", "[cli][build]") {
     auto root = parent / "app";
     add_dep(root, "boost", "1.84.0", {"filesystem", "system"});
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
     auto cmake_text = read_file(root / "build" / "CMakeLists.txt");
@@ -123,7 +123,7 @@ TEST_CASE("cmd_build synthesizes a lockfile entry per dep", "[cli][build]") {
     add_dep(root, "fmt", "10.2.0");
     add_dep(root, "spdlog", "1.13.0");
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE(r.has_value());
 
     auto lock = lockfile::parse(root / "Cargoxx.lock");
@@ -139,22 +139,31 @@ TEST_CASE("cmd_build fails for an unknown dep", "[cli][build]") {
     auto root = parent / "app";
     add_dep(root, "obscurelib", "0.0.1");
 
-    auto r = cmd_build(root, true, false, overlay_path(parent));
+    auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE_FALSE(r.has_value());
     REQUIRE(r.error().code == ErrorCode::LinkdbUnknownPackage);
 }
 
-TEST_CASE("cmd_build without --no-build returns NotImplemented", "[cli][build]") {
+TEST_CASE("cmd_build --release writes a release-typed build/CMakeLists",
+          "[cli][build]") {
+    // The CMAKE_BUILD_TYPE flag itself is set on the cmake command line, not in
+    // the generated CMakeLists.txt — but the same generation runs for both
+    // profiles, so just verify the --release path with --no-build doesn't error.
     auto parent = fresh_dir();
     REQUIRE(cmd_new("app", false, parent).has_value());
     auto root = parent / "app";
+    auto r = cmd_build(root, true, true, std::nullopt, overlay_path(parent));
+    REQUIRE(r.has_value());
+}
 
-    auto r = cmd_build(root, false, false, overlay_path(parent));
+TEST_CASE("cmd_build accepts a --target argument under --no-build",
-    REQUIRE_FALSE(r.has_value());
+          "[cli][build]") {
-    REQUIRE(r.error().code == ErrorCode::NotImplemented);
+    auto parent = fresh_dir();
-    // Files are still generated before the build step would run
+    REQUIRE(cmd_new("app", false, parent).has_value());
-    REQUIRE(std::filesystem::exists(root / "flake.nix"));
+    auto root = parent / "app";
-    REQUIRE(std::filesystem::exists(root / "build" / "CMakeLists.txt"));
+    auto r = cmd_build(root, true, false, std::string{"app_bin"},
+                       overlay_path(parent));
+    REQUIRE(r.has_value());
 }
 
 TEST_CASE("cmd_build is idempotent — second run produces identical files",
@@ -164,12 +173,12 @@ TEST_CASE("cmd_build is idempotent — second run produces identical files",
     auto root = parent / "app";
     add_dep(root, "fmt", "10.2.0");
 
-    REQUIRE(cmd_build(root, true, false, overlay_path(parent)).has_value());
+    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_lock = read_file(root / "Cargoxx.lock");
 
-    REQUIRE(cmd_build(root, true, false, overlay_path(parent)).has_value());
+    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 / "Cargoxx.lock") == first_lock);