From 7c11feab425ff374a96035ae834bee8796ddc099 Mon Sep 17 00:00:00 2001
From: Alex Hamilton <1622250+Aehmlo@users.noreply.github.com>
Date: Tue, 8 Jul 2025 16:05:59 -0400
Subject: [PATCH 1/2] Add configuration/hostname/specialisation env vars

This revision introduces a handful of environmental variables to enable
fallbacks similar to the NH_FLAKE environmental variable family:

* NH_OS_HOSTNAME,
* NH_OS_SPECIALISATION,
* NH_HOME_CONFIGURATION,
* NH_HOME_SPECIALISATION, and
* NH_DARWIN_HOSTNAME.
---
 CHANGELOG.md     |  3 +++
 src/interface.rs | 18 +++++++++---------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b2f686a7..3e1c5481 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,9 @@
 - `nh darwin switch` now shows the output from the `darwin-rebuild` activation.
   This allows you to see more details about the activation from `nix-darwin`, as
   well as `Home Manager`.
+- The `NH_OS_HOSTNAME`, `NH_OS_SPECIALISATION`, `NH_HOME_CONFIGURATION`,
+  `NH_HOME_SPECIALISATION`, and `NH_DARWIN_HOSTNAME` environmental variables are
+  now consulted when determining what attribute/specialisation to use.
 
 ### Fixed
 
diff --git a/src/interface.rs b/src/interface.rs
index 46fdfb76..8bd02ef3 100644
--- a/src/interface.rs
+++ b/src/interface.rs
@@ -185,11 +185,11 @@ pub struct OsRebuildArgs {
     pub update_args: UpdateArgs,
 
     /// When using a flake installable, select this hostname from nixosConfigurations
-    #[arg(long, short = 'H', global = true)]
+    #[arg(long, short = 'H', global = true, env = "NH_OS_HOSTNAME")]
     pub hostname: Option<String>,
 
     /// Explicitly select some specialisation
-    #[arg(long, short)]
+    #[arg(long, short, env = "NH_OS_SPECIALISATION")]
     pub specialisation: Option<String>,
 
     /// Ignore specialisations
@@ -236,7 +236,7 @@ pub struct OsRollbackArgs {
     pub ask: bool,
 
     /// Explicitly select some specialisation
-    #[arg(long, short)]
+    #[arg(long, short, env = "NH_OS_SPECIALISATION")]
     pub specialisation: Option<String>,
 
     /// Ignore specialisations
@@ -280,7 +280,7 @@ pub struct OsReplArgs {
     pub installable: Installable,
 
     /// When using a flake installable, select this hostname from nixosConfigurations
-    #[arg(long, short = 'H', global = true)]
+    #[arg(long, short = 'H', global = true, env = "NH_OS_HOSTNAME")]
     pub hostname: Option<String>,
 }
 
@@ -443,11 +443,11 @@ pub struct HomeRebuildArgs {
     /// Name of the flake homeConfigurations attribute, like username@hostname
     ///
     /// If unspecified, will try <username>@<hostname> and <username>
-    #[arg(long, short)]
+    #[arg(long, short, env = "NH_HOME_CONFIGURATION")]
     pub configuration: Option<String>,
 
     /// Explicitly select some specialisation
-    #[arg(long, short)]
+    #[arg(long, short, env = "NH_HOME_SPECIALISATION")]
     pub specialisation: Option<String>,
 
     /// Ignore specialisations
@@ -483,7 +483,7 @@ pub struct HomeReplArgs {
     /// Name of the flake homeConfigurations attribute, like username@hostname
     ///
     /// If unspecified, will try <username>@<hostname> and <username>
-    #[arg(long, short)]
+    #[arg(long, short, env = "NH_HOME_CONFIGURATION")]
     pub configuration: Option<String>,
 
     /// Extra arguments passed to nix repl
@@ -556,7 +556,7 @@ pub struct DarwinRebuildArgs {
     pub update_args: UpdateArgs,
 
     /// When using a flake installable, select this hostname from darwinConfigurations
-    #[arg(long, short = 'H', global = true)]
+    #[arg(long, short = 'H', global = true, env = "NH_DARWIN_HOSTNAME")]
     pub hostname: Option<String>,
 
     /// Extra arguments passed to nix build
@@ -582,7 +582,7 @@ pub struct DarwinReplArgs {
     pub installable: Installable,
 
     /// When using a flake installable, select this hostname from darwinConfigurations
-    #[arg(long, short = 'H', global = true)]
+    #[arg(long, short = 'H', global = true, env = "NH_DARWIN_HOSTNAME")]
     pub hostname: Option<String>,
 }
 

From f8bd6f3b37f5555dea95192add42a7405bb07ea1 Mon Sep 17 00:00:00 2001
From: Alex Hamilton <1622250+Aehmlo@users.noreply.github.com>
Date: Tue, 8 Jul 2025 16:20:05 -0400
Subject: [PATCH 2/2] Update debug log wording

Since there's no way to distinguish between "the user provided a home
configuration with --configuration" from "the user provided a home
configuration using NH_HOME_CONFIGURATION," this revision updates debug
log wording appropriately.
---
 src/home.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/home.rs b/src/home.rs
index 9fdc26a4..e0e4dd0c 100644
--- a/src/home.rs
+++ b/src/home.rs
@@ -243,7 +243,10 @@ where
                     })?;
 
                 if check_res.map(|s| s.trim().to_owned()).as_deref() == Some("true") {
-                    debug!("Using explicit configuration from flag: {}", config_name);
+                    debug!(
+                        "Using explicit configuration from flag/environment: {}",
+                        config_name
+                    );
                     attribute.push(config_name);
                     if push_drv {
                         attribute.extend(toplevel.clone());