1 files changed, 77 insertions, 0 deletions
diff --git a/third_party/nix/src/nix/eval.cc b/third_party/nix/src/nix/eval.cc
new file mode 100644
index 0000000000..b7058361cb
--- /dev/null
+++ b/third_party/nix/src/nix/eval.cc
@@ -0,0 +1,77 @@
+#include "command.hh"
+#include "common-args.hh"
+#include "shared.hh"
+#include "store-api.hh"
+#include "eval.hh"
+#include "json.hh"
+#include "value-to-json.hh"
+#include "progress-bar.hh"
+
+using namespace nix;
+
+struct CmdEval : MixJSON, InstallableCommand
+{
+    bool raw = false;
+
+    CmdEval()
+    {
+        mkFlag(0, "raw", "print strings unquoted", &raw);
+    }
+
+    std::string name() override
+    {
+        return "eval";
+    }
+
+    std::string description() override
+    {
+        return "evaluate a Nix expression";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To evaluate a Nix expression given on the command line:",
+                "nix eval '(1 + 2)'"
+            },
+            Example{
+                "To evaluate a Nix expression from a file or URI:",
+                "nix eval -f channel:nixos-17.09 hello.name"
+            },
+            Example{
+                "To get the current version of Nixpkgs:",
+                "nix eval --raw nixpkgs.lib.nixpkgsVersion"
+            },
+            Example{
+                "To print the store path of the Hello package:",
+                "nix eval --raw nixpkgs.hello"
+            },
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        if (raw && json)
+            throw UsageError("--raw and --json are mutually exclusive");
+
+        auto state = getEvalState();
+
+        auto v = installable->toValue(*state);
+        PathSet context;
+
+        stopProgressBar();
+
+        if (raw) {
+            std::cout << state->coerceToString(noPos, *v, context);
+        } else if (json) {
+            JSONPlaceholder jsonOut(std::cout);
+            printValueAsJSON(*state, true, *v, jsonOut, context);
+        } else {
+            state->forceValueDeep(*v);
+            std::cout << *v << "\n";
+        }
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdEval>());