Create `nix derivation add` command

Also refine `nix derivation show`'s docs very slightly.

3 files changed, 68 insertions, 4 deletions

diff --git a/src/nix/derivation-add.cc b/src/nix/derivation-add.cc
new file mode 100644
index 000000000..4d91d4538
--- /dev/null
+++ b/src/nix/derivation-add.cc
@@ -0,0 +1,45 @@
+// FIXME: rename to 'nix plan add' or 'nix derivation add'?
+
+#include "command.hh"
+#include "common-args.hh"
+#include "store-api.hh"
+#include "archive.hh"
+#include "derivations.hh"
+#include <nlohmann/json.hpp>
+
+using namespace nix;
+using json = nlohmann::json;
+
+struct CmdAddDerivation : MixDryRun, StoreCommand
+{
+    std::string description() override
+    {
+        return "Add a store derivation";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "derivation-add.md"
+          ;
+    }
+
+    Category category() override { return catUtility; }
+
+    void run(ref<Store> store) override
+    {
+        auto json = nlohmann::json::parse(drainFD(STDIN_FILENO));
+
+        auto drv = Derivation::fromJSON(*store, json);
+
+        auto drvPath = writeDerivation(*store, drv, NoRepair, /* read only */ dryRun);
+
+        drv.checkInvariants(*store, drvPath);
+
+        writeDerivation(*store, drv, NoRepair, dryRun);
+
+        logger->cout("%s", store->printStorePath(drvPath));
+    }
+};
+
+static auto rCmdAddDerivation = registerCommand2<CmdAddDerivation>({"derivation", "add"});
diff --git a/src/nix/derivation-add.md b/src/nix/derivation-add.md
new file mode 100644
index 000000000..f116681ab
--- /dev/null
+++ b/src/nix/derivation-add.md
@@ -0,0 +1,18 @@
+R""(
+
+# Description
+
+This command reads from standard input a JSON representation of a
+[store derivation] to which an [*installable*](./nix.md#installables) evaluates.
+
+Store derivations are used internally by Nix. They are store paths with
+extension `.drv` that represent the build-time dependency graph to which
+a Nix expression evaluates.
+
+[store derivation]: ../../glossary.md#gloss-store-derivation
+
+The JSON format is documented under the [`derivation show`] command.
+
+[`derivation show`]: ./nix3-derivation-show.md
+
+)""
diff --git a/src/nix/derivation-show.md b/src/nix/derivation-show.md
index 1ebe22f65..1296e2885 100644
--- a/src/nix/derivation-show.md
+++ b/src/nix/derivation-show.md
@@ -39,10 +39,11 @@ R""(
 # Description
 
 This command prints on standard output a JSON representation of the
-[store derivation]s to which [*installables*](./nix.md#installables) evaluate. Store derivations
-are used internally by Nix. They are store paths with extension `.drv`
-that represent the build-time dependency graph to which a Nix
-expression evaluates.
+[store derivation]s to which [*installables*](./nix.md#installables) evaluate.
+
+Store derivations are used internally by Nix. They are store paths with
+extension `.drv` that represent the build-time dependency graph to which
+a Nix expression evaluates.
 
 By default, this command only shows top-level derivations, but with
 `--recursive`, it also shows their dependencies.