nixos/nextcloud: drop nextcloud17, deprecate nextcloud18

Both packages will get EOLed within the lifetime of 20.09. `nextcloud17`
can be removed entirely (the attribute-path is kept however to provide
meaningful errors), however `nextcloud18` must be kept as `insecure` to
make sure that users from `nextcloud17` can properly upgrade to
`nextcloud19` on NixOS 20.09.

nixos/doc/manual/release-notes/rl-2009.xml

@@ -834,6 +834,31 @@ CREATE ROLE postgres LOGIN SUPERUSER;
      functionally redundent.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     The package <package>nextcloud17</package> has been removed and <package>nextcloud18</package> was marked as insecure
+     since both of them will <link xlink:href="https://docs.nextcloud.com/server/19/admin_manual/release_schedule.html">
+     will be EOL (end of life) within the lifetime of 20.09</link>.
+    </para>
+    <para>
+     It's necessary to upgrade to <package>nextcloud19</package>:
+     <itemizedlist>
+      <listitem>
+       <para>
+        From <package>nextcloud17</package>, you have to upgrade to <package>nextcloud18</package> first as
+        Nextcloud doesn't allow going multiple major revisions forward in a single upgrade. This is possible
+        by setting <xref linkend="opt-services.nextcloud.package" /> to <package>nextcloud18</package>.
+       </para>
+      </listitem>
+      <listitem>
+       <para>
+        From <package>nextcloud18</package>, it's possible to directly upgrade to <package>nextcloud19</package>
+        by setting <xref linkend="opt-services.nextcloud.package" /> to <package>nextcloud19</package>.
+       </para>
+      </listitem>
+     </itemizedlist>
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 

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

@@ -85,7 +85,7 @@ in {
     package = mkOption {
       type = types.package;
       description = "Which package to use for the Nextcloud instance.";
-      relatedPackages = [ "nextcloud17" "nextcloud18" "nextcloud19" ];
+      relatedPackages = [ "nextcloud18" "nextcloud19" ];
     };
 
     maxUploadSize = mkOption {
@@ -354,7 +354,7 @@ in {
           recommended to upgrade to nextcloud19 after that.
         '')
         ++ (optional (versionOlder cfg.package.version "19") ''
-          A legacy Nextcloud install (from before NixOS 20.09/unstable) may be installed.
+          A legacy Nextcloud install (from before NixOS 20.09) may be installed.
 
           If/After nextcloud18 is installed successfully, you can safely upgrade to
           nextcloud19. If not, please upgrade to nextcloud18 first since Nextcloud doesn't

pkgs/servers/nextcloud/default.nix

@@ -27,14 +27,22 @@ let
     };
   };
 in {
-  nextcloud17 = generic {
-    version = "17.0.6";
-    sha256 = "0qq7lkgzsn1zakfym5bjqzpcisxmgfcdd927ddqlhddy3zvgxrxx";
-  };
+  nextcloud17 = throw ''
+    Nextcloud v17 has been removed from `nixpkgs` as the support for it will be dropped
+    by upstream within the lifetime of NixOS 20.09[1]. Please upgrade to Nextcloud v18 by
+    declaring
+
+        services.nextcloud.package = pkgs.nextcloud18;
+
+    in your NixOS config.
+
+    [1] https://docs.nextcloud.com/server/18/admin_manual/release_schedule.html
+  '';
 
   nextcloud18 = generic {
     version = "18.0.9";
     sha256 = "0rigg5pv2vnxgmjznlvxfc41s00raxa8jhib5vsznhj55qn99jm1";
+    insecure = true;
   };
 
   nextcloud19 = generic {