./Porting/bisect.pl --target=miniperl --start=v5.16.3 --end=v5.18.0 --expect-fail -e 'sub foo::new {} "::foo"->new'
...

commit 7156e69abfd37267e85105c6ec0c449ce4e41523
Author: Father Chrysostomos <sprout@cpan.org>
Date:   Thu Sep 20 08:56:38 2012 -0700

    [perl #105922] Allow any string before ->meth
    
    The rules for filtering out what do not look like package names are
    not logical and disallow valid things like "::main", while allowing
    q"_#@*$!@*^(".
    
    This commit simply lets any non-empty string be used as a package
    name.  If it is a typo, you’ll get an error anyway.  This allows
    autobox-style calls like "3foo"->CORE::uc, or even "3foo"->uc if you
    set up @ISA first.
    
    I made an exception for the empty string because it messes up caches
    somehow and causes subsequent method calls all to be called on the
    main package.  I haven’t looked into that yet.  I don’t know whether
    it’s worth it.
    
    The changes to the tests in cpan/Test-Simple have been submit-
    ted upstream.

Mentioned in perl5180delta:

Class method calls are now allowed on any string, and not just strings beginning with an alphanumeric character. [perl #105922]