fish: query pname and version for completions

Query the `pname` and `version` attributes for completion generation,
if the `name` attribute is not available.

Fixes #2813

modules/programs/fish.nix

@@ -320,8 +320,13 @@ in {
             ${postBuild}
           '';
 
-        generateCompletions = package:
-          pkgs.runCommand "${package.name}-fish-completions" {
+        generateCompletions = let
+          getName = attrs:
+            attrs.name or "${attrs.pname or "«pname-missing»"}-${
+              attrs.version or "«version-missing»"
+            }";
+        in package:
+        pkgs.runCommand "${getName package}-fish-completions" {
           srcs = [ package ] ++ filter (p: p != null)
             (builtins.map (outName: package.${outName} or null)
               config.home.extraOutputsToInstall);