nixos/activation: no output for empty snippets

jameysharp · jameysharp · commit 04da25cd20da · 2019-07-09T01:09:59.000-07:00
There are several empty snippets in a standard configuration. They are
present only for backward compatibility with other snippets which may
have declared dependencies on them.

This patch eliminates the per-snippet boilerplate for empty snippets.
If, someday, we get to the point where there are no non-empty activation
snippets, then this will lead to an empty string where the snippets used
to be.

Note that I didn't want newlines inserted where empty scripts used to be
either, so rather than using textClosureMap with its built-in "\n"
separators, I switched to using the underlying textClosureList, and
adding an extra newline only for non-empty snippets.
diff --git a/nixos/modules/system/activation/activation-script.nix b/nixos/modules/system/activation/activation-script.nix
@@ -8,16 +8,17 @@ let
   sortSnippets = set: let withHeadlines = mapAttrs (a: v:
     let entry = if isString v then noDepEntry v else v;
     in entry // {
-    text = ''
+    text = optionalString (entry.text != "") ''
       #### Activation script snippet ${a}:
       _localstatus=0
       ${entry.text}
 
       if (( _localstatus > 0 )); then
         printf "Activation script snippet '%s' failed (%s)\n" "${a}" "$_localstatus"
       fi
+
     '';
-  }) set; in textClosureMap id (withHeadlines) (attrNames withHeadlines);
+  }) set; in concatStrings (textClosureList withHeadlines (attrNames withHeadlines));
 
   path = with pkgs; map getBin
     [ coreutils
