Introduce types.anything

lib/options.nix

@@ -107,6 +107,10 @@ rec {
   /* "Merge" option definitions by checking that they all have the same value. */
   mergeEqualOption = loc: defs:
     if defs == [] then abort "This case should never happen."
+    # Return early if we only have one element
+    # This also makes it work for functions, because the foldl' below would try
+    # to compare the first element with itself, which is false for functions
+    else if length defs == 1 then (elemAt defs 0).value
     else foldl' (val: def:
       if def.value != val then
         throw "The option `${showOption loc}' has conflicting definitions, in ${showFiles (getFiles defs)}."

lib/tests/modules.sh

@@ -233,6 +233,35 @@ checkConfigError 'infinite recursion encountered' config.foo ./freeform-attrsOf.
 checkConfigError 'The option .* is used but not defined' config.foo ./freeform-lazyAttrsOf.nix ./freeform-unstr-dep-str.nix
 checkConfigOutput 24 config.foo ./freeform-lazyAttrsOf.nix ./freeform-unstr-dep-str.nix ./define-value-string.nix
 
+## types.anything
+# Check that attribute sets are merged recursively
+checkConfigOutput null config.value.foo ./types-anything/nested-attrs.nix
+checkConfigOutput null config.value.l1.foo ./types-anything/nested-attrs.nix
+checkConfigOutput null config.value.l1.l2.foo ./types-anything/nested-attrs.nix
+checkConfigOutput null config.value.l1.l2.l3.foo ./types-anything/nested-attrs.nix
+# Attribute sets that are coercible to strings shouldn't be recursed into
+checkConfigOutput foo config.value.outPath ./types-anything/attrs-coercible.nix
+# Multiple lists aren't concatenated together
+checkConfigError 'The option .* has conflicting definitions' config.value ./types-anything/lists.nix
+# Check that all equalizable atoms can be used as long as all definitions are equal
+checkConfigOutput 0 config.value.int ./types-anything/equal-atoms.nix
+checkConfigOutput false config.value.bool ./types-anything/equal-atoms.nix
+checkConfigOutput '""' config.value.string ./types-anything/equal-atoms.nix
+checkConfigOutput / config.value.path ./types-anything/equal-atoms.nix
+checkConfigOutput null config.value.null ./types-anything/equal-atoms.nix
+checkConfigOutput 0.1 config.value.float ./types-anything/equal-atoms.nix
+# Functions can't be merged together
+checkConfigError "The option .* has conflicting definitions" config.value.multiple-lambdas ./types-anything/functions.nix
+checkConfigOutput '<LAMBDA>' config.value.single-lambda ./types-anything/functions.nix
+# Check that all mk* modifiers are applied
+checkConfigError 'attribute .* not found' config.value.mkiffalse ./types-anything/mk-mods.nix
+checkConfigOutput '{ }' config.value.mkiftrue ./types-anything/mk-mods.nix
+checkConfigOutput 1 config.value.mkdefault ./types-anything/mk-mods.nix
+checkConfigOutput '{ }' config.value.mkmerge ./types-anything/mk-mods.nix
+checkConfigOutput true config.value.mkbefore ./types-anything/mk-mods.nix
+checkConfigOutput 1 config.value.nested.foo ./types-anything/mk-mods.nix
+checkConfigOutput baz config.value.nested.bar.baz ./types-anything/mk-mods.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass

lib/tests/modules/types-anything/attrs-coercible.nix

@@ -0,0 +1,12 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config.value = {
+    outPath = "foo";
+    err = throw "err";
+  };
+
+}

lib/tests/modules/types-anything/equal-atoms.nix

@@ -0,0 +1,26 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config = lib.mkMerge [
+    {
+      value.int = 0;
+      value.bool = false;
+      value.string = "";
+      value.path = /.;
+      value.null = null;
+      value.float = 0.1;
+    }
+    {
+      value.int = 0;
+      value.bool = false;
+      value.string = "";
+      value.path = /.;
+      value.null = null;
+      value.float = 0.1;
+    }
+  ];
+
+}

lib/tests/modules/types-anything/functions.nix

@@ -0,0 +1,17 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config = lib.mkMerge [
+    {
+      value.single-lambda = x: x;
+      value.multiple-lambdas = x: x;
+    }
+    {
+      value.multiple-lambdas = x: x;
+    }
+  ];
+
+}

lib/tests/modules/types-anything/lists.nix

@@ -0,0 +1,16 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config = lib.mkMerge [
+    {
+      value = [ null ];
+    }
+    {
+      value = [ null ];
+    }
+  ];
+
+}

lib/tests/modules/types-anything/mk-mods.nix

@@ -0,0 +1,44 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config = lib.mkMerge [
+    {
+      value.mkiffalse = lib.mkIf false {};
+    }
+    {
+      value.mkiftrue = lib.mkIf true {};
+    }
+    {
+      value.mkdefault = lib.mkDefault 0;
+    }
+    {
+      value.mkdefault = 1;
+    }
+    {
+      value.mkmerge = lib.mkMerge [
+        {}
+      ];
+    }
+    {
+      value.mkbefore = lib.mkBefore true;
+    }
+    {
+      value.nested = lib.mkMerge [
+        {
+          foo = lib.mkDefault 0;
+          bar = lib.mkIf false 0;
+        }
+        (lib.mkIf true {
+          foo = lib.mkIf true (lib.mkForce 1);
+          bar = {
+            baz = lib.mkDefault "baz";
+          };
+        })
+      ];
+    }
+  ];
+
+}

lib/tests/modules/types-anything/nested-attrs.nix

@@ -0,0 +1,22 @@
+{ lib, ... }: {
+
+  options.value = lib.mkOption {
+    type = lib.types.anything;
+  };
+
+  config = lib.mkMerge [
+    {
+      value.foo = null;
+    }
+    {
+      value.l1.foo = null;
+    }
+    {
+      value.l1.l2.foo = null;
+    }
+    {
+      value.l1.l2.l3.foo = null;
+    }
+  ];
+
+}

lib/types.nix

@@ -101,6 +101,42 @@ rec {
   # When adding new types don't forget to document them in
   # nixos/doc/manual/development/option-types.xml!
   types = rec {
+
+    anything = mkOptionType {
+      name = "anything";
+      description = "anything";
+      check = value: true;
+      merge = loc: defs:
+        let
+          getType = value:
+            if isAttrs value && isCoercibleToString value
+            then "stringCoercibleSet"
+            else builtins.typeOf value;
+
+          # Returns the common type of all definitions, throws an error if they
+          # don't have the same type
+          commonType = foldl' (type: def:
+            if getType def.value == type
+            then type
+            else throw "The option `${showOption loc}' has conflicting option types in ${showFiles (getFiles defs)}"
+          ) (getType (head defs).value) defs;
+
+          mergeFunction = {
+            # Recursively merge attribute sets
+            set = (attrsOf anything).merge;
+            # Safe and deterministic behavior for lists is to only accept one definition
+            # listOf only used to apply mkIf and co.
+            list =
+              if length defs > 1
+              then throw "The option `${showOption loc}' has conflicting definitions, in ${showFiles (getFiles defs)}."
+              else (listOf anything).merge;
+            # This is the type of packages, only accept a single definition
+            stringCoercibleSet = mergeOneOption;
+            # Otherwise fall back to only allowing all equal definitions
+          }.${commonType} or mergeEqualOption;
+        in mergeFunction loc defs;
+    };
+
     unspecified = mkOptionType {
       name = "unspecified";
     };

nixos/doc/manual/development/option-types.xml

@@ -21,16 +21,6 @@
   </para>
 
   <variablelist>
-   <varlistentry>
-    <term>
-     <varname>types.attrs</varname>
-    </term>
-    <listitem>
-     <para>
-      A free-form attribute set.
-     </para>
-    </listitem>
-   </varlistentry>
    <varlistentry>
     <term>
      <varname>types.bool</varname>
@@ -64,6 +54,64 @@
      </para>
     </listitem>
    </varlistentry>
+   <varlistentry>
+    <term>
+     <varname>types.anything</varname>
+    </term>
+    <listitem>
+     <para>
+      A type that accepts any value and recursively merges attribute sets together.
+      This type is recommended when the option type is unknown.
+      <example xml:id="ex-types-anything">
+       <title><literal>types.anything</literal> Example</title>
+       <para>
+        Two definitions of this type like
+<programlisting>
+{
+  str = lib.mkDefault "foo";
+  pkg.hello = pkgs.hello;
+  fun.fun = x: x + 1;
+}
+</programlisting>
+<programlisting>
+{
+  str = lib.mkIf true "bar";
+  pkg.gcc = pkgs.gcc;
+  fun.fun = lib.mkForce (x: x + 2);
+}
+</programlisting>
+        will get merged to
+<programlisting>
+{
+  str = "bar";
+  pkg.gcc = pkgs.gcc;
+  pkg.hello = pkgs.hello;
+  fun.fun = x: x + 2;
+}
+</programlisting>
+       </para>
+      </example>
+     </para>
+    </listitem>
+   </varlistentry>
+   <varlistentry>
+    <term>
+     <varname>types.attrs</varname>
+    </term>
+    <listitem>
+     <para>
+      A free-form attribute set.
+      <warning><para>
+       This type will be deprecated in the future because it doesn't recurse
+       into attribute sets, silently drops earlier attribute definitions, and
+       doesn't discharge <literal>lib.mkDefault</literal>, <literal>lib.mkIf
+       </literal> and co. For allowing arbitrary attribute sets, prefer
+       <literal>types.attrsOf types.anything</literal> instead which doesn't
+       have these problems.
+      </para></warning>
+     </para>
+    </listitem>
+   </varlistentry>
   </variablelist>
 
   <para>