nixos-version: output configurationRevision

`nixos-version --configuration-revision` will show the
configurationRevision.

nixos/doc/manual/from_md/release-notes/rl-2305.section.xml

@@ -486,6 +486,13 @@
           <literal>libax25</literal> package.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <literal>nixos-version</literal> now accepts
+          <literal>--configuration-revision</literal> to display more
+          information about the current generation revision
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
 </section>

nixos/doc/manual/man-nixos-version.xml

@@ -21,6 +21,10 @@
     <option>--revision</option>
    </arg>
 
+   <arg>
+    <option>--configuration-revision</option>
+   </arg>
+
    <arg>
     <option>--json</option>
    </arg>
@@ -118,6 +122,23 @@
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term>
+     <option>--configuration-revision</option>
+    </term>
+    <listitem>
+     <para>
+      Show the configuration revision if available. This could be the full SHA1
+      hash of the Git commit of the system flake, if you add
+      <screen>{ system.configurationRevision = self.rev or "dirty"; }</screen>
+      to the <screen>modules</screen> array of your flake.nix system configuration e.g.
+<screen><prompt>$ </prompt>nixos-version --configuration-revision
+aa314ebd1592f6cdd53cb5bba8bcae97d9323de8
+</screen>
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term>
      <option>--json</option>

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -128,3 +128,5 @@ In addition to numerous new and upgraded packages, this release has the followin
 - The new option `services.tailscale.useRoutingFeatures` controls various settings for using Tailscale features like exit nodes and subnet routers. If you wish to use your machine as an exit node, you can set this setting to `server`, otherwise if you wish to use an exit node you can set this setting to `client`. The strict RPF warning has been removed as the RPF will be loosened automatically based on the value of this setting.
 
 - [Xastir](https://xastir.org/index.php/Main_Page) can now access AX.25 interfaces via the `libax25` package.
+
+- `nixos-version` now accepts `--configuration-revision` to display more information about the current generation revision

nixos/modules/installer/tools/nixos-version.sh

@@ -13,6 +13,13 @@ case "$1" in
     fi
     echo "@revision@"
     ;;
+  --configuration-revision)
+    if [[ "@configurationRevision@" =~ "@" ]]; then
+      echo "$0: configuration revision is unknown" >&2
+      exit 1
+    fi
+    echo "@configurationRevision@"
+    ;;
   --json)
     cat <<EOF
 @json@