lib/types: add intBetween

An int type that checks the value range.

lib/types.nix

@@ -114,6 +114,12 @@ rec {
       merge = mergeOneOption;
     };
 
+    intBetween = min: max:
+      addCheck types.int (x: x >= min && x <= max) // {
+        name = "intBetween";
+        description = "integer between ${toString min} and ${toString max} (both inclusively)";
+      };
+
     str = mkOptionType {
       name = "str";
       description = "string";

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

@@ -26,6 +26,17 @@
     <term><varname>types.int</varname></term>
     <listitem><para>An integer.</para></listitem>
   </varlistentry>
+  <varlistentry>
+    <term>
+      <varname>types.intBetween</varname>
+      <replaceable>min</replaceable>
+      <replaceable>max</replaceable>
+    </term>
+    <listitem><para>An integer between <replaceable>min</replaceable>
+        and <replaceable>max</replaceable> (both inclusive).
+        Useful for e.g. port ranges.
+    </para></listitem>
+  </varlistentry>
   <varlistentry>
     <term><varname>types.path</varname></term>
     <listitem><para>A filesystem path, defined as anything that when coerced to