nixos: sound: warn about changes to defaults (18.03)

lib/modules.nix

@@ -310,30 +310,36 @@ rec {
 
     in opt //
       { value = addErrorContext "while evaluating the option `${showOption loc}':" value;
+        inherit (res.defsFinal') highestPrio;
         definitions = map (def: def.value) res.defsFinal;
         files = map (def: def.file) res.defsFinal;
         inherit (res) isDefined;
       };
 
   # Merge definitions of a value of a given type.
   mergeDefinitions = loc: type: defs: rec {
-    defsFinal =
+    defsFinal' =
       let
         # Process mkMerge and mkIf properties.
         defs' = concatMap (m:
           map (value: { inherit (m) file; inherit value; }) (dischargeProperties m.value)
         ) defs;
 
         # Process mkOverride properties.
-        defs'' = filterOverrides defs';
+        defs'' = filterOverrides' defs';
 
         # Sort mkOrder properties.
         defs''' =
           # Avoid sorting if we don't have to.
-          if any (def: def.value._type or "" == "order") defs''
-          then sortProperties defs''
-          else defs'';
-      in defs''';
+          if any (def: def.value._type or "" == "order") defs''.values
+          then sortProperties defs''.values
+          else defs''.values;
+      in {
+        values = defs''';
+        inherit (defs'') highestPrio;
+      };
+
+    defsFinal = defsFinal'.values;
 
     # Type-check the remaining definitions, and merge them.
     mergedValue = foldl' (res: def:
@@ -416,13 +422,18 @@ rec {
 
      Note that "z" has the default priority 100.
   */
-  filterOverrides = defs:
+  filterOverrides = defs: (filterOverrides' defs).values;
+
+  filterOverrides' = defs:
     let
       defaultPrio = 100;
       getPrio = def: if def.value._type or "" == "override" then def.value.priority else defaultPrio;
       highestPrio = foldl' (prio: def: min (getPrio def) prio) 9999 defs;
       strip = def: if def.value._type or "" == "override" then def // { value = def.value.content; } else def;
-    in concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
+    in {
+      values = concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
+      inherit highestPrio;
+    };
 
   /* Sort a list of properties.  The sort priority of a property is
      1000 by default, but can be overridden by wrapping the property

nixos/modules/services/audio/alsa.nix

@@ -1,5 +1,5 @@
 # ALSA sound support.
-{ config, lib, pkgs, ... }:
+{ config, options, lib, pkgs, ... }:
 
 with lib;
 
@@ -78,7 +78,18 @@ in
 
   ###### implementation
 
-  config = mkIf config.sound.enable {
+  config = mkMerge [{
+
+    warnings = optional (options.sound.enable.highestPrio > 1000) ''
+      You don't have `sound.enable` explicitly enabled of disabled. It was
+      enabled by default before a43e33d0e48b2284ac3a2222d7f1965cef66f5e2 and
+      became disabled by default after e349ccc77febd45abbd14be14f7de123ec4a4da2.
+
+      Which means that if you output sound via ALSA it will still works, but
+      your system will no longer save and restore ALSA state between reboots.
+    '';
+
+  } (mkIf config.sound.enable {
 
     environment.systemPackages = [ alsaUtils ];
 
@@ -124,6 +135,6 @@ in
       ];
     };
 
-  };
+  })];
 
 }