lib/modules: Init lib.mkDefinition (#390983)

4 files changed, 96 insertions, 4 deletions

diff --git a/lib/default.nix b/lib/default.nix
index e671fcf9546d..19316addb8cb 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -446,6 +446,7 @@ let
         fixupOptionType
         mkIf
         mkAssert
+        mkDefinition
         mkMerge
         mkOverride
         mkOptionDefault
diff --git a/lib/modules.nix b/lib/modules.nix
index a9ddaf7bda02..7716e855ebb2 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -1097,10 +1097,16 @@ let
         # Process mkMerge and mkIf properties.
         defs' = concatMap (
           m:
-          map (value: {
-            inherit (m) file;
-            inherit value;
-          }) (addErrorContext "while evaluating definitions from `${m.file}':" (dischargeProperties m.value))
+          map (
+            value:
+            if value._type or null == "definition" then
+              value
+            else
+              {
+                inherit (m) file;
+                inherit value;
+              }
+          ) (addErrorContext "while evaluating definitions from `${m.file}':" (dischargeProperties m.value))
         ) defs;
 
         # Process mkOverride properties.
@@ -1365,6 +1371,11 @@ let
     inherit contents;
   };
 
+  /**
+    Return a definition with file location information.
+  */
+  mkDefinition = args@{ file, value, ... }: args // { _type = "definition"; };
+
   mkOverride = priority: content: {
     _type = "override";
     inherit priority content;
@@ -2095,6 +2106,7 @@ private
     mkBefore
     mkChangedOptionModule
     mkDefault
+    mkDefinition
     mkDerivedConfig
     mkFixStrictness
     mkForce
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index e623c0fb55b8..9df6e61797b7 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -673,6 +673,14 @@ checkConfigError 'The option .conflictingPathOptionType. in .*/pathWith.nix. is
 # types.pathWith { inStore = true; absolute = false; }
 checkConfigError 'In pathWith, inStore means the path must be absolute' config.impossiblePathOptionType ./pathWith.nix
 
+# mkDefinition
+# check that mkDefinition 'file' is printed in the error message
+checkConfigError 'Cannot merge definitions.*\n\s*- In .file.*\n\s*- In .other.*' config.conflict ./mkDefinition.nix
+checkConfigError 'A definition for option .viaOptionDefault. is not of type .boolean.*' config.viaOptionDefault ./mkDefinition.nix
+checkConfigOutput '^true$' config.viaConfig ./mkDefinition.nix
+checkConfigOutput '^true$' config.mkMerge ./mkDefinition.nix
+checkConfigOutput '^true$' config.mkForce ./mkDefinition.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/lib/tests/modules/mkDefinition.nix b/lib/tests/modules/mkDefinition.nix
new file mode 100644
index 000000000000..0a807090fa28
--- /dev/null
+++ b/lib/tests/modules/mkDefinition.nix
@@ -0,0 +1,71 @@
+{ lib, ... }:
+let
+  inherit (lib)
+    mkOption
+    mkDefinition
+    mkOptionDefault
+    ;
+in
+{
+  imports = [
+    {
+      _file = "file";
+      options.conflict = mkOption {
+        default = 1;
+      };
+      config.conflict = mkDefinition {
+        file = "other";
+        value = mkOptionDefault 42;
+      };
+    }
+    {
+      # Check that mkDefinition works within 'config'
+      options.viaConfig = mkOption { };
+      config.viaConfig = mkDefinition {
+        file = "other";
+        value = true;
+      };
+    }
+    {
+      # Check mkMerge can wrap mkDefinitions
+      # Not the other way around
+      options.mkMerge = mkOption {
+        type = lib.types.bool;
+      };
+      config.mkMerge = lib.mkMerge [
+        (mkDefinition {
+          file = "a.nix";
+          value = true;
+        })
+        (mkDefinition {
+          file = "b.nix";
+          value = true;
+        })
+      ];
+    }
+    {
+      # Check mkDefinition can use mkForce on the value
+      # Not the other way around
+      options.mkForce = mkOption {
+        type = lib.types.bool;
+        default = false;
+      };
+      config.mkForce = mkDefinition {
+        file = "other";
+        value = lib.mkForce true;
+      };
+    }
+    {
+      # Currently expects an error
+      # mkDefinition doesn't work on option default
+      # This is a limitation and might be resolved in the future
+      options.viaOptionDefault = mkOption {
+        type = lib.types.bool;
+        default = mkDefinition {
+          file = "other";
+          value = true;
+        };
+      };
+    }
+  ];
+}