Add new C API for working with derivations

Also test the APIs we just added.

src/libstore-tests/data/derivation/ca/self-contained.json

@@ -0,0 +1,23 @@
+{
+  "args": [
+    "-c",
+    "echo $name foo > $out"
+  ],
+  "builder": "/bin/sh",
+  "env": {
+    "builder": "/bin/sh",
+    "name": "myname",
+    "out": "/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9",
+    "system": "x86_64-linux"
+  },
+  "inputDrvs": {},
+  "inputSrcs": [],
+  "name": "myname",
+  "outputs": {
+    "out": {
+      "hashAlgo": "sha256",
+      "method": "nar"
+    }
+  },
+  "system": "x86_64-linux"
+}

src/libstore-tests/main.cc

@@ -0,0 +1,15 @@
+#include <gtest/gtest.h>
+
+#include "nix/store/tests/test-main.hh"
+
+using namespace nix;
+
+int main(int argc, char ** argv)
+{
+    auto res = testMainForBuidingPre(argc, argv);
+    if (res)
+        return res;
+
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}

src/libstore-tests/meson.build

@@ -66,6 +66,7 @@ sources = files(
   'local-overlay-store.cc',
   'local-store.cc',
   'machines.cc',
+  'main.cc',
   'nar-info-disk-cache.cc',
   'nar-info.cc',
   'nix_api_store.cc',

src/libstore-tests/nix_api_store.cc

@@ -1,7 +1,10 @@
+#include <fstream>
+
 #include "nix_api_util.h"
 #include "nix_api_store.h"
 
 #include "nix/store/tests/nix_api_store.hh"
+#include "nix/store/globals.hh"
 #include "nix/util/tests/string_callback.hh"
 #include "nix/util/url.hh"
 
@@ -197,4 +200,60 @@ TEST_F(nix_api_util_context, nix_store_real_path_binary_cache)
     ASSERT_STREQ(path_raw.c_str(), rp.c_str());
 }
 
+template<typename F>
+struct LambdaAdapter
+{
+    F fun;
+
+    template<typename... Args>
+    static inline auto call(LambdaAdapter<F> * ths, Args... args)
+    {
+        return ths->fun(args...);
+    }
+
+    template<typename... Args>
+    static auto call_void(void * ths, Args... args)
+    {
+        return call(static_cast<LambdaAdapter<F> *>(ths), args...);
+    }
+};
+
+TEST_F(nix_api_store_test_base, build_from_json)
+{
+    // FIXME get rid of these
+    nix::experimentalFeatureSettings.set("extra-experimental-features", "ca-derivations");
+    nix::settings.substituters = {};
+
+    auto * store = open_local_store();
+
+    std::filesystem::path unitTestData{getenv("_NIX_TEST_UNIT_DATA")};
+
+    std::ifstream t{unitTestData / "derivation/ca/self-contained.json"};
+    std::stringstream buffer;
+    buffer << t.rdbuf();
+
+    auto * drv = nix_derivation_from_json(ctx, store, buffer.str().c_str());
+    assert_ctx_ok();
+    ASSERT_NE(drv, nullptr);
+
+    auto * drvPath = nix_add_derivation(ctx, store, drv);
+    assert_ctx_ok();
+    ASSERT_NE(drv, nullptr);
+
+    auto cb = LambdaAdapter{.fun = [&](const char * outname, const StorePath * outPath) {
+        auto is_valid_path = nix_store_is_valid_path(ctx, store, outPath);
+        ASSERT_EQ(is_valid_path, true);
+    }};
+
+    auto ret = nix_store_realise(
+        ctx, store, drvPath, static_cast<void *>(&cb), decltype(cb)::call_void<const char *, const StorePath *>);
+    assert_ctx_ok();
+    ASSERT_EQ(ret, NIX_OK);
+
+    // Clean up
+    nix_store_path_free(drvPath);
+    nix_derivation_free(drv);
+    nix_store_free(store);
+}
+
 } // namespace nixC