Refactor current profile detection

src/nix/deployment/mod.rs

@@ -428,16 +428,18 @@ impl Deployment {
 
             if !target.config.replace_unknown_profiles {
                 job.message("Checking remote profile...".to_string())?;
-                match host.active_derivation_known().await {
-                    Ok(_) => {
+
+                let profile = host.get_main_system_profile().await?;
+
+                if profile.exists() {
                     job.message("Remote profile known".to_string())?;
-                    }
-                    Err(e) => {
-                        if arc_self.options.force_replace_unknown_profiles {
-                            job.message("warning: remote profile is unknown, but unknown profiles are being ignored".to_string())?;
                 } else {
-                            return Err(e);
-                        }
+                    if arc_self.options.force_replace_unknown_profiles {
+                        job.message("Warning: Remote profile is unknown, but unknown profiles are being ignored".to_string())?;
+                    } else {
+                        return Err(NixError::ActiveProfileUnknown {
+                            store_path: profile,
+                        });
                     }
                 }
             }

src/nix/host/local.rs

@@ -6,7 +6,7 @@ use async_trait::async_trait;
 use tokio::process::Command;
 
 use super::{CopyDirection, CopyOptions, Host, key_uploader};
-use crate::nix::{StorePath, Profile, Goal, NixError, NixResult, NixCommand, Key, SYSTEM_PROFILE};
+use crate::nix::{StorePath, Profile, Goal, NixError, NixResult, NixCommand, Key, SYSTEM_PROFILE, CURRENT_PROFILE};
 use crate::util::CommandExecution;
 use crate::job::JobHandle;
 
@@ -90,8 +90,19 @@ impl Host for Local {
 
         result
     }
-    async fn active_derivation_known(&mut self) -> NixResult<bool> {
-        Ok(true)
+
+    async fn get_main_system_profile(&mut self) -> NixResult<StorePath> {
+        let paths = Command::new("sh")
+            .args(&["-c", &format!("readlink -e {} || readlink -e {}", SYSTEM_PROFILE, CURRENT_PROFILE)])
+            .capture_output()
+            .await?;
+
+        let path = paths.lines().into_iter().next()
+            .ok_or(NixError::FailedToGetCurrentProfile)?
+            .to_string()
+            .try_into()?;
+
+        Ok(path)
     }
 
     fn set_job(&mut self, job: Option<JobHandle>) {

src/nix/host/mod.rs

@@ -110,8 +110,12 @@ pub trait Host: Send + Sync + std::fmt::Debug {
         Err(NixError::Unsupported)
     }
 
-    /// Check if the active profile is known to the host running Colmena
-    async fn active_derivation_known(&mut self) -> NixResult<bool>;
+    /// Returns the main system profile on the host.
+    ///
+    /// This may _not_ be the system profile that's currently activated!
+    /// It will first try `/nix/var/nix/profiles/system`, falling back
+    /// to `/run/current-system` if it doesn't exist.
+    async fn get_main_system_profile(&mut self) -> NixResult<StorePath>;
 
     /// Activates a system profile on the host, if it runs NixOS.
     ///

src/nix/host/ssh.rs

@@ -7,7 +7,7 @@ use async_trait::async_trait;
 use tokio::process::Command;
 
 use super::{CopyDirection, CopyOptions, Host, key_uploader};
-use crate::nix::{StorePath, Profile, Goal, NixResult, NixCommand, NixError, Key, SYSTEM_PROFILE};
+use crate::nix::{StorePath, Profile, Goal, NixResult, NixCommand, NixError, Key, SYSTEM_PROFILE, CURRENT_PROFILE};
 use crate::util::CommandExecution;
 use crate::job::JobHandle;
 
@@ -78,26 +78,19 @@ impl Host for Ssh {
         let command = self.ssh(command);
         self.run_command(command).await
     }
-    async fn active_derivation_known(&mut self) -> NixResult<bool> {
-        let paths = self.ssh(&["realpath", SYSTEM_PROFILE])
-            .capture_output()
-            .await;
+    async fn get_main_system_profile(&mut self) -> NixResult<StorePath> {
+        let command = format!("\"readlink -e {} || readlink -e {}\"", SYSTEM_PROFILE, CURRENT_PROFILE);
 
-        match paths {
-            Ok(paths) => {
-                if let Some(path) = paths.lines().into_iter().next() {
-                    let remote_profile: StorePath = path.to_string().try_into().unwrap();
-                    if remote_profile.exists() {
-                        return Ok(true);
-                    }
-                    return Err(NixError::ActiveProfileUnknown {
-                        store_path: path.to_string(),
-                    });
-                }
-                return Ok(false);
-            }
-            Err(e) => Err(e),
-        }
+        let paths = self.ssh(&["sh", "-c", &command])
+            .capture_output()
+            .await?;
+
+        let path = paths.lines().into_iter().next()
+            .ok_or(NixError::FailedToGetCurrentProfile)?
+            .to_string()
+            .try_into()?;
+
+        Ok(path)
     }
     fn set_job(&mut self, job: Option<JobHandle>) {
         self.job = job;

src/nix/mod.rs

@@ -44,8 +44,12 @@ pub use flake::Flake;
 pub mod node_filter;
 pub use node_filter::NodeFilter;
 
+/// Path to the main system profile.
 pub const SYSTEM_PROFILE: &str = "/nix/var/nix/profiles/system";
 
+/// Path to the system profile that's currently active.
+pub const CURRENT_PROFILE: &str = "/run/current-system";
+
 pub type NixResult<T> = Result<T, NixError>;
 
 #[non_exhaustive]
@@ -81,8 +85,11 @@ pub enum NixError {
     #[snafu(display("Invalid NixOS system profile"))]
     InvalidProfile,
 
-    #[snafu(display("Unknown active profile: {}", store_path))]
-    ActiveProfileUnknown { store_path: String },
+    #[snafu(display("Unknown active profile: {:?}", store_path))]
+    ActiveProfileUnknown { store_path: StorePath },
+
+    #[snafu(display("Could not determine current profile"))]
+    FailedToGetCurrentProfile,
 
     #[snafu(display("Current Nix version does not support Flakes"))]
     NoFlakesSupport,