nixpkgs.lib: Add types.strMatching

lib/types.nix

@@ -174,6 +174,13 @@ rec {
       merge = mergeOneOption;
     };
 
+    strMatching = pattern: mkOptionType {
+      name = "strMatching ${escapeNixString pattern}";
+      description = "string matching the pattern ${pattern}";
+      check = x: str.check x && builtins.match pattern x != null;
+      inherit (str) merge;
+    };
+
     # Merge multiple definitions by concatenating them (with the given
     # separator between the values).
     separatedString = sep: mkOptionType rec {

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

@@ -110,6 +110,12 @@
     <listitem><para>A string. Multiple definitions are concatenated with a 
         collon <literal>":"</literal>.</para></listitem>
   </varlistentry>
+  <varlistentry>
+    <term><varname>types.strMatching</varname></term>
+    <listitem><para>A string matching a specific regular expression. Multiple
+    definitions cannot be merged.  The regular expression is processed using
+    <literal>builtins.match</literal>.</para></listitem>
+  </varlistentry>
 </variablelist>
 
  </section>