feat: simplify and unify writing in nix.conf

Co-authored-by: Jörg Thalheim <Mic92@users.noreply.github.com>

Author: sabify

src/nixos-anywhere.sh

@@ -1036,37 +1036,56 @@ main() {
     sshConnection="root@${sshHost}"
   fi
 
-  # Get substituters from the machine and add them to the installer
-  if [[ ${machineSubstituters} == "y" && -n ${flake} ]]; then
-    substituters=$(nix --extra-experimental-features 'nix-command flakes' eval --apply toString "${flake}"#"${flakeAttr}".nix.settings.substituters)
-    trustedPublicKeys=$(nix --extra-experimental-features 'nix-command flakes' eval --apply toString "${flake}"#"${flakeAttr}".nix.settings.trusted-public-keys)
-
-    runSsh sh <<SSH || true
-mkdir -p ~/.config/nix
-echo "extra-substituters = ${substituters}" >> ~/.config/nix/nix.conf
-echo "extra-trusted-public-keys = ${trustedPublicKeys}" >> ~/.config/nix/nix.conf
-SSH
-  fi
-
-  # Get system-features with a specific cpu architecture from the machine and add them to the installer
   if [[ -n ${flake} ]]; then
-    system_features=$(nix --extra-experimental-features 'nix-command flakes' eval --apply 'x: toString (x.nix.settings.system-features or "")' "${flake}#${flakeAttr}")
-    if [[ -z ${system_features} ]]; then
-      system_features=$(runSshNoTty -o ConnectTimeout=10 nix --extra-experimental-features 'nix-command' config show system-features)
-    fi
-
-    platform_arch=$(nix --extra-experimental-features 'nix-command flakes' eval --apply 'x: toString (x.nixpkgs.hostPlatform.gcc.arch or "")' "${flake}#${flakeAttr}")
-    if [[ -n ${platform_arch} ]]; then
-      system_features="${system_features} gccarch-${platform_arch}"
-    fi
-
-    # deduplicate the features
-    system_features=$(echo "${system_features}" | tr ' ' '\n' | sort -u | tr '\n' ' ' | sed 's/ $//')
-
-    runSsh sh <<SSH
+    system_features=$(runSshNoTty -o ConnectTimeout=10 nix --extra-experimental-features 'nix-command' config show system-features 2>/dev/null || true)
+
+    # First, try to evaluate all nix settings from the flake in one go
+    nixConfContent=$(nix --extra-experimental-features 'nix-command flakes' eval --raw --apply "
+      config:
+      let
+        settings = config.nix.settings or {};
+        gccArch = config.nixpkgs.hostPlatform.gcc.arch or null;
+
+        # Check if system-features are defined in configuration
+        configFeatures = settings.system-features or null;
+        hasConfigFeatures = configFeatures != null && configFeatures != [];
+
+        remoteFeatures = let
+            remoteFeaturesStr = \"${system_features}\";
+            # Parse remote features string (space-separated) into list
+            remoteFeaturesList = if remoteFeaturesStr != \"\" then
+              builtins.filter (x: x != \"\") (builtins.split \" +\" remoteFeaturesStr)
+            else [];
+          in remoteFeaturesList;
+
+        # Combine base features (config or remote) with platform-specific features
+        baseFeatures = if hasConfigFeatures then configFeatures else remoteFeatures;
+        # At least one of nix.settings.system-features or nixpkgs.hostPlatform.gcc.arch has been explicitly defined
+        allFeatures = if (gccArch != null) || hasConfigFeatures then baseFeatures ++ (if gccArch != null then [\"gccarch-\${gccArch}\"] else []) else [];
+
+        # Deduplicate using listToAttrs trick
+        uniqueFeatures = builtins.attrNames (builtins.listToAttrs (map (f: { name = f; value = true; }) allFeatures));
+
+        substituters = builtins.toString (settings.substituters or []);
+        trustedPublicKeys = builtins.toString (settings.trusted-public-keys or []);
+        systemFeatures = builtins.toString uniqueFeatures;
+
+        # Helper function for optional config lines
+        optionalLine = cond: line: if cond then line + \"\n\" else \"\";
+        useSubstituters = \"${machineSubstituters}\" == \"y\";
+      in
+        optionalLine (useSubstituters && substituters != \"\") \"extra-substituters = \${substituters}\"
+        + optionalLine (useSubstituters && trustedPublicKeys != \"\") \"extra-trusted-public-keys = \${trustedPublicKeys}\"
+        + optionalLine (systemFeatures != \"\") \"system-features = \${systemFeatures}\"
+    " "${flake}#${flakeAttr}")
+
+      # Write to nix.conf if we have any content
+    if [[ -n ${nixConfContent} ]]; then
+      runSsh sh <<SSH
 mkdir -p ~/.config/nix
-echo "system-features = ${system_features}" >> ~/.config/nix/nix.conf
+echo "${nixConfContent}" >> ~/.config/nix/nix.conf
 SSH
+    fi
   fi
 
   if [[ ${phases[disko]} == 1 ]]; then