nix build: Add '--profile' flag

This replaces 'nix-env --set'. For example:

  $ nix build --profile /nix/var/nix/profiles/system \
      ~/Misc/eelco-configurations:nixosConfigurations.vyr.config.system.build.toplevel

updates the NixOS system profile from a flake.

This could have been a separate command (e.g. 'nix set-profile') but
1) '--profile' is pretty similar to '--out-link'; and 2) '--profile'
could be useful for other command (like 'nix dev-shell').

1 files changed, 41 insertions, 0 deletions

diff --git a/src/nix/command.cc b/src/nix/command.cc
index 89fa0cba4..8191cb831 100644
--- a/src/nix/command.cc
+++ b/src/nix/command.cc
@@ -1,6 +1,7 @@
 #include "command.hh"
 #include "store-api.hh"
 #include "derivations.hh"
+#include "profiles.hh"
 
 namespace nix {
 
@@ -81,4 +82,44 @@ void StorePathCommand::run(ref<Store> store)
     run(store, *storePaths.begin());
 }
 
+MixProfile::MixProfile()
+{
+    mkFlag()
+        .longName("profile")
+        .description("profile to update")
+        .labels({"path"})
+        .dest(&profile);
+}
+
+void MixProfile::updateProfile(const Path & storePath)
+{
+    if (!profile) return;
+    auto store = getStore().dynamic_pointer_cast<LocalFSStore>();
+    if (!store) throw Error("'--profile' is not supported for this Nix store");
+    switchLink(*profile,
+        createGeneration(
+            ref<LocalFSStore>(store),
+            *profile, storePath));
+}
+
+void MixProfile::updateProfile(const Buildables & buildables)
+{
+    if (!profile) return;
+
+    std::optional<Path> result;
+
+    for (auto & buildable : buildables) {
+        for (auto & output : buildable.outputs) {
+            if (result)
+                throw Error("'--profile' requires that the arguments produce a single store path, but there are multiple");
+            result = output.second;
+        }
+    }
+
+    if (!result)
+        throw Error("'--profile' requires that the arguments produce a single store path, but there are none");
+
+    updateProfile(*result);
+}
+
 }