1 files changed, 44 insertions, 4 deletions

diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 2b91faa64..4cd7d77a0 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -222,7 +222,7 @@ struct CmdFlakeCheck : FlakeCommand
     {
         addFlag({
             .longName = "no-build",
-            .description = "do not build checks",
+            .description = "Do not build checks.",
             .handler = {&build, false}
         });
     }
@@ -573,7 +573,7 @@ struct CmdFlakeInitCommon : virtual Args, EvalCommand
         addFlag({
             .longName = "template",
             .shortName = 't',
-            .description = "the template to use",
+            .description = "The template to use.",
             .labels = {"template"},
             .handler = {&templateUrl},
             .completer = {[&](size_t, std::string_view prefix) {
@@ -717,7 +717,7 @@ struct CmdFlakeClone : FlakeCommand
         addFlag({
             .longName = "dest",
             .shortName = 'f',
-            .description = "destination path",
+            .description = "Clone the flake to path *dest*.",
             .labels = {"path"},
             .handler = {&destDir}
         });
@@ -807,7 +807,7 @@ struct CmdFlakeShow : FlakeCommand
     {
         addFlag({
             .longName = "legacy",
-            .description = "show the contents of the 'legacyPackages' output",
+            .description = "Show the contents of the `legacyPackages` output.",
             .handler = {&showLegacy, true}
         });
     }
@@ -960,6 +960,45 @@ struct CmdFlakeShow : FlakeCommand
     }
 };
 
+struct CmdFlakePrefetch : FlakeCommand, MixJSON
+{
+    CmdFlakePrefetch()
+    {
+    }
+
+    std::string description() override
+    {
+        return "download the source tree denoted by a flake reference into the Nix store";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "flake-prefetch.md"
+          ;
+    }
+
+    void run(ref<Store> store) override
+    {
+        auto originalRef = getFlakeRef();
+        auto resolvedRef = originalRef.resolve(store);
+        auto [tree, lockedRef] = resolvedRef.fetchTree(store);
+        auto hash = store->queryPathInfo(tree.storePath)->narHash;
+
+        if (json) {
+            auto res = nlohmann::json::object();
+            res["storePath"] = store->printStorePath(tree.storePath);
+            res["hash"] = hash.to_string(SRI, true);
+            logger->cout(res.dump());
+        } else {
+            notice("Downloaded '%s' to '%s' (hash '%s').",
+                lockedRef.to_string(),
+                store->printStorePath(tree.storePath),
+                hash.to_string(SRI, true));
+        }
+    }
+};
+
 struct CmdFlake : NixMultiCommand
 {
     CmdFlake()
@@ -973,6 +1012,7 @@ struct CmdFlake : NixMultiCommand
                 {"clone", []() { return make_ref<CmdFlakeClone>(); }},
                 {"archive", []() { return make_ref<CmdFlakeArchive>(); }},
                 {"show", []() { return make_ref<CmdFlakeShow>(); }},
+                {"prefetch", []() { return make_ref<CmdFlakePrefetch>(); }},
             })
     {
     }