[0/9] RFC better type-printing

[Tom Tromey <tromey at redhat dot com>]

This patch series improves gdb's type printing for some typical C++
code.  It also adds a bit of Python API to let programs supply some type
printing functionality.

To see what this is about, try printing this type:

    typedef std::unordered_set<std::string> Set;

I've appended the current output, see [1].
It is ridiculously long -- unreadable really.

Now see [2], which is the improved output.  GDB now substitutes template
parameter names when it can, and it substitutes typedef names defined in
the class as well.

If you read [2] carefully you'll see that the template parameters are
duplicated in the [with ...] clause.  This is a GCC bug:

    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54410

Also, the output could be even prettier if we could omit defaulted
template parameters.  I filed a GCC bug for this:

    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49090

Note that [2] also shows the effect of Python printers.  In particular,
Python is responsible for the "std::string" display there.

This series adds a few new toggles to type printing.  In particular, it
adds formatting flags to ptype and whatis, a couple of new settings to
control some defaults, and new commands for manipulating the Python
printers.

I've split the series as best I can.  Some of the patches are trivial;
but I also tried to split the most complicated one to make it easier to
read.

Tom

[1]

type = 
    class std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > 
    : public std::_Hashtable<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> > {
  public:
    void unordered_set(unsigned long, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::hasher &, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::key_equal &, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::allocator_type &);
    void unordered_set(
    std::initializer_list<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, unsigned long, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::hasher &, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::key_equal &, 
    const std::unordered_set<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::allocator_type &);

    typedef 
    std::_Hashtable<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::size_type size_type;
    typedef 
    std::__detail::_Hash_code_base<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__detail::_Identity, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, true>::hasher hasher;
    typedef 
    std::_Hashtable<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::key_equal key_equal;
    typedef 
    std::_Hashtable<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Identity, std::equal_to<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::hash<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::allocator_type allocator_type;
}


[2]

type = class 
    std::unordered_set<std::string, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::string> > [with _Value = std::string, 
         _Hash = std::hash<std::string>, _Pred = std::equal_to<std::string>, 
         _Alloc = std::allocator<std::string>, _Value = std::string, 
         _Hash = std::hash<std::string>, _Pred = std::equal_to<std::string>, 
         _Alloc = std::allocator<std::string>] 
        : public std::_Hashtable<_Value, _Value, _Alloc, std::__detail::_Identity, _Pred, _Hash, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> > {
  public:
    void unordered_set(size_type, const _Hash &, const _Pred &, 
        const _Alloc &);
    void unordered_set(std::initializer_list<_Value>, size_type, 
        const _Hash &, const _Pred &, const _Alloc &);

    typedef std::_Hashtable<_Value, _Value, _Alloc, std::__detail::_Identity, _Pred, _Hash, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, true, true> >::size_type size_type;
    typedef _Hash hasher;
    typedef _Pred key_equal;
    typedef _Alloc allocator_type;
}