lib.modules: Change class declaration in module to _class

doc/module-system/module-system.chapter.md

@@ -30,7 +30,7 @@ This is in contrast to `config._module.args`, which is only available after all
 
 #### `class` {#module-system-lib-evalModules-param-class}
 
-If the `class` attribute is set and non-`null`, the module system will reject `imports` with a different `class`.
+If the `class` attribute is set and non-`null`, the module system will reject `imports` with a different `_class` declaration.
 
 The `class` value should be a string in lower [camel case](https://en.wikipedia.org/wiki/Camel_case).
 

lib/modules.nix

@@ -371,10 +371,10 @@ let
         if class != null
         then
           m:
-            if m.class != null -> m.class == class
+            if m._class != null -> m._class == class
             then m
             else
-              throw "The module ${m._file or m.key} was imported into ${class} instead of ${m.class}."
+              throw "The module ${m._file or m.key} was imported into ${class} instead of ${m._class}."
         else
           m: m;
 
@@ -475,28 +475,28 @@ let
         else config;
     in
     if m ? config || m ? options then
-      let badAttrs = removeAttrs m ["_file" "key" "disabledModules" "imports" "options" "config" "meta" "freeformType" "class"]; in
+      let badAttrs = removeAttrs m ["_class" "_file" "key" "disabledModules" "imports" "options" "config" "meta" "freeformType"]; in
       if badAttrs != {} then
         throw "Module `${key}' has an unsupported attribute `${head (attrNames badAttrs)}'. This is caused by introducing a top-level `config' or `options' attribute. Add configuration attributes immediately on the top level instead, or move all of them (namely: ${toString (attrNames badAttrs)}) into the explicit `config' attribute."
       else
         { _file = toString m._file or file;
+          _class = m._class or null;
           key = toString m.key or key;
           disabledModules = m.disabledModules or [];
           imports = m.imports or [];
           options = m.options or {};
           config = addFreeformType (addMeta (m.config or {}));
-          class = m.class or null;
         }
     else
       # shorthand syntax
       lib.throwIfNot (isAttrs m) "module ${file} (${key}) does not look like a module."
       { _file = toString m._file or file;
+        _class = m._class or null;
         key = toString m.key or key;
         disabledModules = m.disabledModules or [];
         imports = m.require or [] ++ m.imports or [];
         options = {};
-        config = addFreeformType (removeAttrs m ["_file" "key" "disabledModules" "require" "imports" "freeformType"]);
+        config = addFreeformType (removeAttrs m ["_class" "_file" "key" "disabledModules" "require" "imports" "freeformType"]);
-        class = null;
       };
 
   applyModuleArgsIfFunction = key: f: args@{ config, options, lib, ... }:

lib/tests/modules/class-check.nix

@@ -63,14 +63,14 @@
         modules = [
           ./module-class-is-nixos.nix
           { _file = "foo.nix#darwinModules.default";
-            class = "darwin";
+            _class = "darwin";
             config = {};
             imports = [];
           }
         ];
       };
 
-    sub.nixosOk = { config = {}; class = "nixos"; };
+    sub.nixosOk = { _class = "nixos"; };
     sub.nixosFail = { imports = [ ./module-class-is-darwin.nix ]; };
   };
 }

lib/tests/modules/module-class-is-darwin.nix

@@ -1,4 +1,4 @@
 {
-  class = "darwin";
+  _class = "darwin";
   config = {};
 }

lib/tests/modules/module-class-is-nixos.nix

@@ -1,4 +1,4 @@
 {
-  class = "nixos";
+  _class = "nixos";
   config = {};
 }