pkgs: diff-flake: add 'host' and 'shell' options

pkgs/diff-flake/diff-flake

@@ -20,6 +20,21 @@ sanitize_output() {
     fi
 }
 
+add_shell() {
+    local SYSTEM
+    if [ $# -gt 0 ] && [ -n "$1" ]; then
+        SYSTEM="$1"
+    else
+        SYSTEM="$(nix eval --raw --impure --expr 'builtins.currentSystem')"
+    fi
+    # Use 'inputDerivation' attribute to make sure that it is build-able
+    FLAKE_OUTPUTS+=("devShell.$SYSTEM.inputDerivation")
+}
+
+add_host() {
+    FLAKE_OUTPUTS+=("nixosConfigurations.$1.config.system.build.toplevel")
+}
+
 usage() {
     print_err "Usage: $0 [option]... [-- [nix build option]...]"
     print_err ""
@@ -37,11 +52,23 @@ usage() {
     print_err "  -p, --previous-rev"
     print_err "    which git revision should be considered the 'previous' state,"
     print_err "    defaults to HEAD~"
+    print_err "  --host [name]"
+    print_err "    specify the name of a NixOS output configuration whose"
+    print_err "    closure should be diffed, can be used multiple times"
+    print_err "    if no host name is given, defaults to current hostname"
+    print_err "  --shell [system]"
+    print_err "    specify a specific system's devShell output whose closure"
+    print_err "    should be diffed, can be used multiple times"
+    print_err "    if no system is given, defaults to current system"
     print_err ""
     print_err "when no flake outputs are specified, automatically queries for"
     print_err "all NixOS configurations, and devShell for current system"
 }
 
+is_option() {
+    [ $# -gt 0 ] && [[ $1 =~ ^(-.|--.*)$ ]]
+}
+
 parse_args() {
     while [ $# -gt 0 ]; do
         opt="$1"
@@ -68,6 +95,22 @@ parse_args() {
                 PREVIOUS_REV="$(git rev-parse "$1")"
                 shift
                 ;;
+            --host)
+                if [ $# -gt 0 ] && ! is_option "$1"; then
+                    add_host "$1"
+                    shift
+                else
+                    add_host "$(hostname)"
+                fi
+                ;;
+            --shell)
+                if [ $# -gt 0 ] && ! is_option "$1"; then
+                    add_shell "$1"
+                    shift
+                else
+                    add_shell
+                fi
+                ;;
             --)
                 NIX_BUILD_ARGS=("$@")
                 break
@@ -87,15 +130,6 @@ list_nixos_configurations() {
         --raw
 }
 
-fill_default_outputs() {
-    for host in $(list_nixos_configurations); do
-        FLAKE_OUTPUTS+=("nixosConfigurations.$host.config.system.build.toplevel")
-    done
-
-    # Use 'inputDerivation' attribute to make sure that it is build-able
-    FLAKE_OUTPUTS+=("devShell.$(nix eval --raw --impure --expr 'builtins.currentSystem').inputDerivation")
-}
-
 diff_output() {
     local PREV NEW;
     PREV="$(mktemp --dry-run)"
@@ -115,7 +149,10 @@ diff_output() {
 parse_args "$@"
 
 if [ "${#FLAKE_OUTPUTS[@]}" -eq 0 ]; then
-    fill_default_outputs
+    for host in $(list_nixos_configurations); do
+        add_host "$host"
+    done
+    add_shell
 fi
 
 for out in "${FLAKE_OUTPUTS[@]}"; do