Add new C API for working with derivations

Also test the APIs we just added.

src/libstore-c/nix_api_store.cc

@@ -166,11 +166,44 @@ void nix_store_path_free(StorePath * sp)
     delete sp;
 }
 
+void nix_derivation_free(nix_derivation * drv)
+{
+    delete drv;
+}
+
 StorePath * nix_store_path_clone(const StorePath * p)
 {
     return new StorePath{p->path};
 }
 
+nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store, const char * json)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto drv = nix::Derivation::fromJSON(*store->ptr, nlohmann::json::parse(json));
+
+        auto drvPath = nix::writeDerivation(*store->ptr, drv, nix::NoRepair, /* read only */ true);
+
+        drv.checkInvariants(*store->ptr, drvPath);
+
+        return new nix_derivation{drv};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
+StorePath * nix_add_derivation(nix_c_context * context, Store * store, nix_derivation * derivation)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        auto ret = nix::writeDerivation(*store->ptr, derivation->drv, nix::NoRepair);
+
+        return new StorePath{ret};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
 nix_err nix_store_copy_closure(nix_c_context * context, Store * srcStore, Store * dstStore, StorePath * path)
 {
     if (context)

src/libstore-c/nix_api_store.h

@@ -23,6 +23,8 @@ extern "C" {
 typedef struct Store Store;
 /** @brief Nix store path */
 typedef struct StorePath StorePath;
+/** @brief Nix Derivation */
+typedef struct nix_derivation nix_derivation;
 
 /**
  * @brief Initializes the Nix store library
@@ -207,6 +209,32 @@ nix_err nix_store_realise(
 nix_err
 nix_store_get_version(nix_c_context * context, Store * store, nix_get_string_callback callback, void * user_data);
 
+/**
+ * @brief Create a `nix_derivation` from a JSON representation of that derivation.
+ *
+ * @param[out] context Optional, stores error information.
+ * @param[in] store nix store reference.
+ * @param[in] json JSON of the derivation as a string.
+ */
+nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store, const char * json);
+
+/**
+ * @brief Add the given `nix_derivation` to the given store
+ *
+ * @param[out] context Optional, stores error information.
+ * @param[in] store nix store reference. The derivation will be inserted here.
+ * @param[in] derivation nix_derivation to insert into the given store.
+ */
+StorePath * nix_add_derivation(nix_c_context * context, Store * store, nix_derivation * derivation);
+
+/**
+ * @brief Deallocate a `nix_derivation`
+ *
+ * Does not fail.
+ * @param[in] drv the derivation to free
+ */
+void nix_derivation_free(nix_derivation * drv);
+
 /**
  * @brief Copy the closure of `path` from `srcStore` to `dstStore`.
  *

src/libstore-c/nix_api_store_internal.h

@@ -1,6 +1,7 @@
 #ifndef NIX_API_STORE_INTERNAL_H
 #define NIX_API_STORE_INTERNAL_H
 #include "nix/store/store-api.hh"
+#include "nix/store/derivations.hh"
 
 extern "C" {
 
@@ -14,6 +15,11 @@ struct StorePath
     nix::StorePath path;
 };
 
+struct nix_derivation
+{
+    nix::Derivation drv;
+};
+
 } // extern "C"
 
 #endif