I'm using MooseX::Declare (which uses MooseX::Method::Signatures (which uses Moose::Meta::TypeConstraint )) with long signatures such as in the following example:

use 5.010;
use MooseX::Declare;

class Manager { };
class Server { has 'hdr' => ( is => 'rw' ) };

class Archive {

    #.. other methods

    method init_archive ( Manager   :$mgr!,
                          Int       :$debug,
                          Str       :$user!,
                          Str       :$pass!,
                          Str       :$path!
                            where {
                                $_ !~ /:/ and $_ =~ m{^[\\/]}
                            },
                          HashRef   :$target_args!
                            where {
                                ($_->{NR} and $_->{SID} and $_->{dt})
                                or
                                ($_->{NR} and $_->{SID} and $_->{hostn
+ame})
                            },
                          Server    :$master
                            where {
                                defined $_->hdr
                            }
                        ) {

        say "ARCHIVE INITIALISED";
        return $self;
    }

}

Archive->new->init_archive( user        => 'boldra',
                            pass        => 'secret',
                            path        => 'd:\\data\\DYV\\',
#                            path        => '//hostname/d$/data/DYV',
                            mgr         => Manager->new,
                            target_args => { 
                                  NR        => '01', 
                                  SID       => 1, 
                                  hostname  => 'localhost' },
                            master      => Server->new( { hdr => 1 } )
+ );
[download]

If you look closely, you'll see that I'm breaking the constraint on 'path', by supplying what looks like a local windows path, instead of the expected network path.

The problem you see when you run my example, is that the error message is a little too verbose to be useful, and somewhat defeats the purpose of having signatures:

Validation failed for 'MooseX::Types::Structured::Tuple[MooseX::Types:
+:Structured::Tuple[Object],MooseX::Types::Structured::Dict[mgr,Manage
+r,debug,MooseX::Types::Structured::Optional[Int],user,Str,pass,Str,pa
+th,__ANON__,target_args,__ANON__,master,MooseX::Types::Structured::Op
+tional[__ANON__]]]' failed with value [ [ Archive=HASH(0x2a012a8) ], 
+{ master => Server=HASH(0x2a7ce38), mgr => Manager=HASH(0x2a708e0), p
+ass => "secret", path => "d:\data\DYV\", target_args => HASH(0x1aa3ad
+8), user => "boldra" } ], Internal Validation Error is: Validation fa
+iled for 'MooseX::Types::Structured::Dict[mgr,Manager,debug,MooseX::T
+ypes::Structured::Optional[Int],user,Str,pass,Str,path,__ANON__,targe
+t_args,__ANON__,master,MooseX::Types::Structured::Optional[__ANON__]]
+' failed with value { master => Server={ hdr => 1 }, mgr => Manager={
+  }, pass => "secret", path => "d:\data\DYV\", target_args => { NR =>
+ 01, SID => 1, hostname => "localhost" }, user => "boldra" } at /usr/
+lib/perl5/site_perl/5.10/MooseX/Method/Signatures/Meta/Method.pm line
+ 445
    MooseX::Method::Signatures::Meta::Method::validate('MooseX::Method
+::Signatures::Meta::Method=HASH(0x2a7cec8)', 'ARRAY(0x29e1788)') call
+ed at /usr/lib/perl5/site_perl/5.10/MooseX/Method/Signatures/Meta/Met
+hod.pm line 145
    Archive::init_archive('Archive=HASH(0x2a012a8)', 'user', 'boldra',
+ 'pass', 'secret', 'path', 'd:\data\DYV\', 'mgr', 'Manager=HASH(0x2a7
+08e0)', ...) called at /home/boldra/archive_test.pl line 40
[download]

After looking at the source of Moose::Meta::TypeConstraint, it looks like it's equipped to provide quite precise messages (including looking for a message method on the class type). So here's the questions:

1. Am I doing something wrong in my signatures? What would I change in the code above to get a clear message as which argument is wrong and where?
2. If this is a shortcoming of MooseX::Method::Signatures, but it's not because of Moose::Meta::TypeConstraint, where should the fix be? The MooseX::Method::Signature doc (BUGS, CAVEATS) suggests that a bug should be raised if the messages are not good. But which module really has the bug?
3. Is there perhaps an easier way to get what I'm after (precise error messages on subroutine/method validation) with a different module?

Thanks for reading this far!

(Bart suggested yesterday that I ask this on a Moose forum, but I thought I'd start here. Feel free to post links to other forums, cpanforums.com/dist/moose seems pretty dead)