nixos/discourse: Update plugin documentation

Update the documentation regarding plugins to reflect recent changes.

(cherry picked from commit 20548f050e72a789ebbfe413b0fe7aa815e55c27)

nixos/modules/services/web-apps/discourse.nix

@@ -475,21 +475,16 @@ in
       plugins = lib.mkOption {
         type = lib.types.listOf lib.types.package;
         default = [];
-        example = ''
+        example = lib.literalExample ''
-          [
+          with config.services.discourse.package.plugins; [
-            (pkgs.fetchFromGitHub {
+            discourse-canned-replies
-              owner = "discourse";
+            discourse-github
-              repo = "discourse-spoiler-alert";
-              rev = "e200cfa571d252cab63f3d30d619b370986e4cee";
-              sha256 = "0ya69ix5g77wz4c9x9gmng6l25ghb5xxlx3icr6jam16q14dzc33";
-            })
           ];
         '';
         description = ''
-          <productname>Discourse</productname> plugins to install as a
+          Plugins to install as part of
-          list of derivations. As long as a plugin supports the
+          <productname>Discourse</productname>, expressed as a list of
-          standard install method, packaging it should only require
+          derivations.
-          fetching its source with an appropriate fetcher.
         '';
       };
 

nixos/modules/services/web-apps/discourse.xml

@@ -262,9 +262,31 @@ services.discourse = {
     <para>
       You can install <productname>Discourse</productname> plugins
       using the <xref linkend="opt-services.discourse.plugins" />
-      option. As long as a plugin supports the standard install
+      option. Pre-packaged plugins are provided in
-      method, packaging it should only require fetching its source
+      <literal>&lt;your_discourse_package_here&gt;.plugins</literal>. If
-      with an appropriate fetcher.
+      you want the full suite of plugins provided through
+      <literal>nixpkgs</literal>, you can also set the <xref
+      linkend="opt-services.discourse.package" /> option to
+      <literal>pkgs.discourseAllPlugins</literal>.
+    </para>
+
+    <para>
+      Plugins can be built with the
+      <literal>&lt;your_discourse_package_here&gt;.mkDiscoursePlugin</literal>
+      function. Normally, it should suffice to provide a
+      <literal>name</literal> and <literal>src</literal> attribute. If
+      the plugin has Ruby dependencies, however, they need to be
+      packaged in accordance with the <link
+      xlink:href="https://nixos.org/manual/nixpkgs/stable/#developing-with-ruby">Developing
+      with Ruby</link> section of the Nixpkgs manual and the
+      appropriate gem options set in <literal>bundlerEnvArgs</literal>
+      (normally <literal>gemdir</literal> is sufficient). A plugin's
+      Ruby dependencies are listed in its
+      <filename>plugin.rb</filename> file as function calls to
+      <literal>gem</literal>. To construct the corresponding
+      <filename>Gemfile</filename>, run <command>bundle
+      init</command>, then add the <literal>gem</literal> lines to it
+      verbatim.
     </para>
 
     <para>
@@ -280,7 +302,10 @@ services.discourse = {
     <para>
       For example, to add the <link
       xlink:href="https://github.com/discourse/discourse-spoiler-alert">discourse-spoiler-alert</link>
-      plugin and disable it by default:
+      and <link
+      xlink:href="https://github.com/discourse/discourse-solved">discourse-solved</link>
+      plugins, and disable <literal>discourse-spoiler-alert</literal>
+      by default:
 
 <programlisting>
 services.discourse = {
@@ -301,13 +326,9 @@ services.discourse = {
     <link linkend="opt-services.discourse.mail.outgoing.passwordFile">passwordFile</link> = "/path/to/smtp_password_file";
   };
   <link linkend="opt-services.discourse.mail.incoming.enable">mail.incoming.enable</link> = true;
-  <link linkend="opt-services.discourse.mail.incoming.enable">plugins</link> = [
+  <link linkend="opt-services.discourse.mail.incoming.enable">plugins</link> = with config.services.discourse.package.plugins; [
-    (pkgs.fetchFromGitHub {
+    discourse-spoiler-alert
-      owner = "discourse";
+    discourse-solved
-      repo = "discourse-spoiler-alert";
-      rev = "e200cfa571d252cab63f3d30d619b370986e4cee";
-      sha256 = "0ya69ix5g77wz4c9x9gmng6l25ghb5xxlx3icr6jam16q14dzc33";
-    })
   ];
   <link linkend="opt-services.discourse.siteSettings">siteSettings</link> = {
     plugins = {