Use nixpkgs functions to check dovecot version

mail-server/dovecot-version.nix

@@ -1,12 +0,0 @@
-{ dovecot, gawk, gnused, jq, runCommand }:
-
-runCommand "dovecot-version" {
-  buildInputs = [dovecot gnused jq];
-} ''
-  jq -n  \
-    --arg dovecot_version "$(dovecot --version |
-        sed 's/\([0-9.]*\).*/\1/' |
-        awk -F '.' '{ print $1"."$2"."$3 }')" \
-    '[$dovecot_version | split("."), ["major", "minor", "patch"]]
-       | transpose | map( { (.[1]): .[0] | tonumber }) | add' > $out
-''

mail-server/dovecot.nix

@@ -23,9 +23,6 @@ let
 
   maildirLayoutAppendix = lib.optionalString cfg.useFsLayout ":LAYOUT=fs";
 
-  dovecotVersion = builtins.fromJSON
-    (builtins.readFile (pkgs.callPackage ./dovecot-version.nix {}));
-
   # maildir in format "/${domain}/${user}"
   dovecotMaildir = "maildir:${cfg.mailDirectory}/%d/%n${maildirLayoutAppendix}";
 
@@ -79,7 +76,7 @@ in
 
         mail_access_groups = ${vmailGroupName}
         ssl = required
-        ${lib.optionalString (dovecotVersion.major == 2 && dovecotVersion.minor >= 3) ''
+        ${lib.optionalString (lib.versionAtLeast (lib.getVersion pkgs.dovecot) "2.3") ''
           ssl_dh = <${certificateDirectory}/dh.pem
         ''}
 

mail-server/systemd.nix

@@ -19,11 +19,8 @@
 let
   cfg = config.mailserver;
 
-  createDhParameterFile = let
-     dovecotVersion = builtins.fromJSON
-       (builtins.readFile (pkgs.callPackage ./dovecot-version.nix {}));
-    in lib.optionalString
-      (dovecotVersion.major == 2 && dovecotVersion.minor >= 3)
+  createDhParameterFile =
+    lib.optionalString (lib.versionAtLeast (lib.getVersion pkgs.dovecot) "2.3")
       ''
         # Create a dh parameter file
         if [ ! -s "${cfg.certificateDirectory}/dh.pem" ]