support for standalone home specialisation

README.md

@@ -71,7 +71,6 @@ Nh supports both Flakes and classical NixOS configurations:
 You might want to check `nh os --help` for other values and the defaults from
 environment variables.
 
-
 #### Specialisations support
 
 Nh is capable of detecting which specialisation you are running, so it runs the proper activation script.
@@ -91,6 +90,24 @@ To do so, you need to give nh some information of the spec that is currently run
 }
 ```
 
+#### Home-Manager
+
+Home specialisations are read from `~/.local/share/home-manager/specialisation`. The config would look like this:
+
+```nix
+{config, pkgs, ...}: {
+  specialisation."foo".configuration = {
+    xdg.dataFile."home-manager/specialisation".text = "foo";
+    # ..rest of config
+  };
+
+  specialisation."bar".configuration = {
+    xdg.dataFile."home-manager/specialisation".text = "bar";
+    # ..rest of config
+  };
+}
+```
+
 
 # Status
 

src/home.rs

@@ -69,11 +69,30 @@ impl HomeRebuildArgs {
 
         debug!(?prev_generation);
 
+        let spec_location =
+            PathBuf::from(std::env::var("HOME")?).join(".local/share/home-manager/specialisation");
+
+        let current_specialisation = std::fs::read_to_string(spec_location.to_str().unwrap()).ok();
+
+        let target_specialisation = if self.no_specialisation {
+            None
+        } else {
+            current_specialisation.or(self.specialisation)
+        };
+
+        debug!("target_specialisation: {target_specialisation:?}");
+
+        let target_profile = match &target_specialisation {
+            None => out_path,
+            Some(spec) => Box::new(out_path.get_path().join("specialisation").join(spec)),
+        };
+
+        // just do nothing for None case (fresh installs)
         if let Some(generation) = prev_generation {
             Command::new("nvd")
                 .arg("diff")
                 .arg(generation)
-                .arg(out_path.get_path())
+                .arg(target_profile.get_path())
                 .message("Comparing changes")
                 .run()?;
         }
@@ -96,13 +115,13 @@ impl HomeRebuildArgs {
             env::set_var("HOME_MANAGER_BACKUP_EXT", ext);
         }
 
-        Command::new(out_path.get_path().join("activate"))
+        Command::new(target_profile.get_path().join("activate"))
             .message("Activating configuration")
             .run()?;
 
         // Make sure out_path is not accidentally dropped
         // https://docs.rs/tempfile/3.12.0/tempfile/index.html#early-drop-pitfall
-        drop(out_path);
+        drop(target_profile);
 
         Ok(())
     }

src/interface.rs

@@ -281,6 +281,14 @@ pub struct HomeRebuildArgs {
     #[arg(long, short)]
     pub configuration: Option<String>,
 
+    /// Explicitely select some specialisation
+    #[arg(long, short)]
+    pub specialisation: Option<String>,
+
+    /// Ignore specialisations
+    #[arg(long, short = 'S')]
+    pub no_specialisation: bool,
+
     /// Extra arguments passed to nix build
     #[arg(last = true)]
     pub extra_args: Vec<String>,