Add new C API for working with derivations

Also test the APIs we just added.

src/libstore-test-support/include/nix/store/tests/meson.build

@@ -9,4 +9,5 @@ headers = files(
   'outputs-spec.hh',
   'path.hh',
   'protocol.hh',
+  'test-main.hh',
 )

src/libstore-test-support/include/nix/store/tests/nix_api_store.hh

@@ -12,33 +12,32 @@
 #include <gtest/gtest.h>
 
 namespace nixC {
-class nix_api_store_test : public nix_api_util_context
+
+class nix_api_store_test_base : public nix_api_util_context
 {
 public:
-    nix_api_store_test()
+    nix_api_store_test_base()
     {
         nix_libstore_init(ctx);
-        init_local_store();
     };
 
-    ~nix_api_store_test() override
+    ~nix_api_store_test_base() override
     {
-        nix_store_free(store);
-
-        for (auto & path : std::filesystem::recursive_directory_iterator(nixDir)) {
-            std::filesystem::permissions(path, std::filesystem::perms::owner_all);
+        if (exists(std::filesystem::path{nixDir})) {
+            for (auto & path : std::filesystem::recursive_directory_iterator(nixDir)) {
+                std::filesystem::permissions(path, std::filesystem::perms::owner_all);
+            }
+            std::filesystem::remove_all(nixDir);
         }
-        std::filesystem::remove_all(nixDir);
     }
 
-    Store * store;
     std::string nixDir;
     std::string nixStoreDir;
     std::string nixStateDir;
     std::string nixLogDir;
 
 protected:
-    void init_local_store()
+    Store * open_local_store()
     {
 #ifdef _WIN32
         // no `mkdtemp` with MinGW
@@ -66,11 +65,37 @@ protected:
 
         const char ** params[] = {p1, p2, p3, nullptr};
 
-        store = nix_store_open(ctx, "local", params);
+        auto * store = nix_store_open(ctx, "local", params);
         if (!store) {
             std::string errMsg = nix_err_msg(nullptr, ctx, nullptr);
-            ASSERT_NE(store, nullptr) << "Could not open store: " << errMsg;
+            EXPECT_NE(store, nullptr) << "Could not open store: " << errMsg;
+            assert(store);
         };
+        return store;
     }
 };
+
+class nix_api_store_test : public nix_api_store_test_base
+{
+public:
+    nix_api_store_test()
+        : nix_api_store_test_base{}
+    {
+        init_local_store();
+    };
+
+    ~nix_api_store_test() override
+    {
+        nix_store_free(store);
+    }
+
+    Store * store;
+
+protected:
+    void init_local_store()
+    {
+        store = open_local_store();
+    }
+};
+
 } // namespace nixC

src/libstore-test-support/include/nix/store/tests/test-main.hh

@@ -0,0 +1,13 @@
+#pragma once
+
+///@file
+
+namespace nix {
+
+/**
+ * Call this for a GTest test suite that will including performing Nix
+ * builds, before running tests.
+ */
+int testMainForBuidingPre(int argc, char ** argv);
+
+} // namespace nix

src/libstore-test-support/meson.build

@@ -34,6 +34,7 @@ sources = files(
   'derived-path.cc',
   'outputs-spec.cc',
   'path.cc',
+  'test-main.cc',
 )
 
 subdir('include/nix/store/tests')

src/libstore-test-support/test-main.cc

@@ -0,0 +1,47 @@
+#include <cstdlib>
+
+#include "nix/store/globals.hh"
+#include "nix/util/logging.hh"
+
+#include "nix/store/tests/test-main.hh"
+
+namespace nix {
+
+int testMainForBuidingPre(int argc, char ** argv)
+{
+    if (argc > 1 && std::string_view(argv[1]) == "__build-remote") {
+        printError("test-build-remote: not supported in libexpr unit tests");
+        return EXIT_FAILURE;
+    }
+
+    // Disable build hook. We won't be testing remote builds in these unit tests. If we do, fix the above build hook.
+    settings.buildHook = {};
+
+    // No substituters, unless a test specifically requests.
+    settings.substituters = {};
+
+#ifdef __linux__ // should match the conditional around sandboxBuildDir declaration.
+
+    // When building and testing nix within the host's Nix sandbox, our store dir will be located in the host's
+    // sandboxBuildDir, e.g.: Host
+    //   storeDir = /nix/store
+    //   sandboxBuildDir = /build
+    // This process
+    //   storeDir = /build/foo/bar/store
+    //   sandboxBuildDir = /build
+    // However, we have a rule that the store dir must not be inside the storeDir, so we need to pick a different
+    // sandboxBuildDir.
+    settings.sandboxBuildDir = "/test-build-dir-instead-of-usual-build-dir";
+#endif
+
+#ifdef __APPLE__
+    // Avoid this error, when already running in a sandbox:
+    // sandbox-exec: sandbox_apply: Operation not permitted
+    settings.sandboxMode = smDisabled;
+    setEnv("_NIX_TEST_NO_SANDBOX", "1");
+#endif
+
+    return EXIT_SUCCESS;
+}
+
+} // namespace nix