krops writeDeploy: add flake parameter

With flake set, nixos-rebuild deploys that flake from the build target's
source directory, with flakes enabled for the command.  The deployment fails
with an error message unless Nix on the build target supports flakes.

2 files changed, 18 insertions, 2 deletions

diff --git a/README.md b/README.md
index 39ed6cb..7c17d6d 100644
--- a/README.md
+++ b/README.md
@@ -129,6 +129,16 @@ architecture.
 Run `nixos-rebuild` immediately without building the system in a dedicated `nix
 build` step.
 
+### `flake` (optional)
+
+Name of the source containing the flake to deploy, optionally followed by `#`
+and the name of the NixOS configuration, e.g. `"myconf#myhost"`.  If the source
+draws inputs from other sources, its generated flake gets deployed, see
+[Flake inputs from sources](#flake-inputs-from-sources).  This makes
+`nixos-rebuild` use `--flake`, and requires Nix with flake support (Nix 2.4 or
+later) on the build target.  Without the name of the NixOS configuration,
+`nixos-rebuild` uses the host name of the build target.
+
 ### `force` (optional, defaults to false)
 
 Create the sentinel file (`/var/src/.populate`) before syncing the new source.
diff --git a/pkgs/krops/default.nix b/pkgs/krops/default.nix
index 04c38cf..93f9d0e 100644
--- a/pkgs/krops/default.nix
+++ b/pkgs/krops/default.nix
@@ -5,13 +5,18 @@ in
 { nix, openssh, populate, writers }: rec {
 
   rebuild = {
+    flake ? null,
     useNixOutputMonitor
   }:
   args: target:
     runShell target {}
       (withNixOutputMonitor target useNixOutputMonitor /* sh */ ''
+        ${lib.optionalString (flake != null)
+          (lib.shell.requireFlakes "deploying a flake")}
         NIX_PATH=${lib.escapeShellArg target.path} \
-        nixos-rebuild ${lib.escapeShellArgs args}
+        nixos-rebuild ${lib.escapeShellArgs (args ++ lib.optionals (flake != null) [
+          "--flake" "${target.path}/${flake}"
+        ])}
       '');
 
   runShell = target: {
@@ -91,6 +96,7 @@ in
     buildTarget ? null,
     crossDeploy ? false,
     fast ? null,
+    flake ? null,
     force ? false,
     operation ? "switch",
     source,
@@ -109,7 +115,7 @@ in
         ${lib.optionalString (buildTarget' != target')
           (populate { inherit backup force source; target = buildTarget'; })}
         ${populate { inherit backup force source; target = target'; }}
-        ${rebuild { inherit useNixOutputMonitor; } ([
+        ${rebuild { inherit flake useNixOutputMonitor; } ([
           operation
         ] ++ lib.optionals crossDeploy [
           "--no-build-nix"