release-notes: Add nixpkgs.hostPlatform changes

nixos/doc/manual/from_md/release-notes/rl-2211.section.xml

@@ -31,6 +31,65 @@
           <literal>stdenv.buildPlatform.canExecute stdenv.hostPlatform</literal>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The <literal>nixpkgs.hostPlatform</literal> and
+          <literal>nixpkgs.buildPlatform</literal> options have been
+          added. These cover and override the
+          <literal>nixpkgs.{system,localSystem,crossSystem}</literal>
+          options.
+        </para>
+        <itemizedlist spacing="compact">
+          <listitem>
+            <para>
+              <literal>hostPlatform</literal> is the platform or
+              <quote><literal>system</literal></quote> string of the
+              NixOS system described by the configuration.
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              <literal>buildPlatform</literal> is the platform that is
+              responsible for building the NixOS configuration. It
+              defaults to the <literal>hostPlatform</literal>, for a
+              non-cross build configuration. To cross compile, set
+              <literal>buildPlatform</literal> to a different value.
+            </para>
+          </listitem>
+        </itemizedlist>
+        <para>
+          The new options convey the same information, but with fewer
+          options, and following the Nixpkgs terminology.
+        </para>
+        <para>
+          The existing options
+          <literal>nixpkgs.{system,localSystem,crossSystem}</literal>
+          have not been formally deprecated, to allow for evaluation of
+          the change and to allow for a transition period so that in
+          time the ecosystem can switch without breaking compatibility
+          with any supported NixOS release.
+        </para>
+      </listitem>
+      <listitem>
+        <para>
+          <literal>nixos-generate-config</literal> now generates
+          configurations that can be built in pure mode. This is
+          achieved by setting the new
+          <literal>nixpkgs.hostPlatform</literal> option.
+        </para>
+        <para>
+          You may have to unset the <literal>system</literal> parameter
+          in <literal>lib.nixosSystem</literal>, or similarly remove
+          definitions of the
+          <literal>nixpkgs.{system,localSystem,crossSystem}</literal>
+          options.
+        </para>
+        <para>
+          Alternatively, you can remove the
+          <literal>hostPlatform</literal> line and use NixOS like you
+          would in NixOS 22.05 and earlier.
+        </para>
+      </listitem>
       <listitem>
         <para>
           PHP now defaults to PHP 8.1, updated from 8.0.

nixos/doc/manual/release-notes/rl-2211.section.md

@@ -17,6 +17,33 @@ In addition to numerous new and upgraded packages, this release has the followin
   built for `stdenv.hostPlatform` (i.e. produced by `stdenv.cc`) by evaluating
   `stdenv.buildPlatform.canExecute stdenv.hostPlatform`.
 
+- The `nixpkgs.hostPlatform` and `nixpkgs.buildPlatform` options have been added.
+  These cover and override the `nixpkgs.{system,localSystem,crossSystem}` options.
+
+   - `hostPlatform` is the platform or "`system`" string of the NixOS system
+     described by the configuration.
+   - `buildPlatform` is the platform that is responsible for building the NixOS
+     configuration. It defaults to the `hostPlatform`, for a non-cross
+     build configuration. To cross compile, set `buildPlatform` to a different
+     value.
+
+  The new options convey the same information, but with fewer options, and
+  following the Nixpkgs terminology.
+
+  The existing options `nixpkgs.{system,localSystem,crossSystem}` have not
+  been formally deprecated, to allow for evaluation of the change and to allow
+  for a transition period so that in time the ecosystem can switch without
+  breaking compatibility with any supported NixOS release.
+
+- `nixos-generate-config` now generates configurations that can be built in pure
+  mode. This is achieved by setting the new `nixpkgs.hostPlatform` option.
+
+  You may have to unset the `system` parameter in `lib.nixosSystem`, or similarly
+  remove definitions of the `nixpkgs.{system,localSystem,crossSystem}` options.
+
+  Alternatively, you can remove the `hostPlatform` line and use NixOS like you
+  would in NixOS 22.05 and earlier.
+
 - PHP now defaults to PHP 8.1, updated from 8.0.
 
 - `hardware.nvidia` has a new option `open` that can be used to opt in the opensource version of NVIDIA kernel driver. Note that the driver's support for GeForce and Workstation GPUs is still alpha quality, see [NVIDIA Releases Open-Source GPU Kernel Modules](https://developer.nvidia.com/blog/nvidia-releases-open-source-gpu-kernel-modules/) for the official announcement.