Re: [PATCH] Fix gdb FilteringTypePrinter (again)

["François Dumont" <frs.dumont@gmail.com>]

On 16/11/22 12:54, Jonathan Wakely wrote:
> On Wed, 16 Nov 2022 at 11:35, Jonathan Wakely <jwakely@redhat.com> wrote:
>> On Wed, 16 Nov 2022 at 06:04, François Dumont <frs.dumont@gmail.com> wrote:
>>> On 15/11/22 17:17, Jonathan Wakely wrote:
>>>> On 06/10/22 19:38 +0200, François Dumont wrote:
>>>>> Hi
>>>>>
>>>>> Looks like the previous patch was not enough. When using it in the
>>>>> context of a build without dual abi and versioned namespace I started
>>>>> having failures again. I guess I hadn't rebuild everything properly.
>>>>>
>>>>> This time I think the problem was in those lines:
>>>>>
>>>>>              if self.type_obj == type_obj:
>>>>>                  return strip_inline_namespaces(self.name)
>>>>>
>>>>> I've added a call to gdb.types.get_basic_type so that we do not compare
>>>>> a type with its typedef.
>>>>>
>>>>> Thanks for the pointer to the doc !
>>>>>
>>>>> Doing so I eventually use your code Jonathan to make FilteringTypeFilter
>>>>> more specific to a given instantiation.
>>>>>
>>>>>      libstdc++: Fix gdb FilteringTypePrinter
>>>>>
>>>>>      Once we found a matching FilteringTypePrinter instance we look for
>>>>> the associated
>>>>>      typedef and check that the returned Python Type is equal to the
>>>>> Type to recognize.
>>>>>      But gdb Python Type includes properties to distinguish a typedef
>>>>> from the actual
>>>>>      type. So use gdb.types.get_basic_type to check if we are indeed on
>>>>> the same type.
>>>>>
>>>>>      Additionnaly enhance FilteringTypePrinter matching mecanism by
>>>>> introducing targ1 that,
>>>>>      if not None, will be used as the 1st template parameter.
>>>>>
>>>>>      libstdc++-v3/ChangeLog:
>>>>>
>>>>>              * python/libstdcxx/v6/printers.py (FilteringTypePrinter):
>>>>> Rename 'match' field
>>>>>              'template'. Add self.targ1 to specify the first template
>>>>> parameter of the instantiation
>>>>>              to match.
>>>>>              (add_one_type_printer): Add targ1 optional parameter,
>>>>> default to None.
>>>>>              Use gdb.types.get_basic_type to compare the type to
>>>>> recognize and the type
>>>>>              returned from the typedef lookup.
>>>>>              (register_type_printers): Adapt calls to
>>>>> add_one_type_printers.
>>>>>
>>>>> Tested under Linux x86_64 normal, version namespace with or without dual
>>>>> abi.
>>>>>
>>>>> François
>>>>>
>>>>> diff --git a/libstdc++-v3/python/libstdcxx/v6/printers.py
>>>>> b/libstdc++-v3/python/libstdcxx/v6/printers.py
>>>>> index 0fa7805183e..52339b247d8 100644
>>>>> --- a/libstdc++-v3/python/libstdcxx/v6/printers.py
>>>>> +++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
>>>>> @@ -2040,62 +2040,72 @@ def add_one_template_type_printer(obj, name,
>>>>> defargs):
>>>>>
>>>>> class FilteringTypePrinter(object):
>>>>>      r"""
>>>>> -    A type printer that uses typedef names for common template
>>>>> specializations.
>>>>> +    A type printer that uses typedef names for common template
>>>>> instantiations.
>>>>>
>>>>>      Args:
>>>>> -        match (str): The class template to recognize.
>>>>> +        template (str): The class template to recognize.
>>>>>          name (str): The typedef-name that will be used instead.
>>>>> +        targ1 (str): The first template argument.
>>>>> +            If arg1 is provided (not None), only template
>>>>> instantiations with this type
>>>>> +            as the first template argument, e.g. if
>>>>> template='basic_string<targ1'
>>>>>
>>>>> -    Checks if a specialization of the class template 'match' is the
>>>>> same type
>>>>> +    Checks if an instantiation of the class template 'template' is
>>>>> the same type
>>>>>      as the typedef 'name', and prints it as 'name' instead.
>>>>>
>>>>> -    e.g. if an instantiation of std::basic_istream<C, T> is the same
>>>>> type as
>>>>> +    e.g. for template='basic_istream', name='istream', if any
>>>>> instantiation of
>>>>> +    std::basic_istream<C, T> is the same type as std::istream then
>>>>> print it as
>>>>> +    std::istream.
>>>>> +
>>>>> +    e.g. for template='basic_istream', name='istream', targ1='char',
>>>>> if any
>>>>> +    instantiation of std::basic_istream<char, T> is the same type as
>>>>>      std::istream then print it as std::istream.
>>>>>      """
>>>> These are template specializations, not instantiations. Please undo
>>>> the changes to the comments, because the comments are 100% correct
>>>> now, and would become wrong with this patch.
>>>>
>>>> template<class T, class U> struct foo { };
>>>> using F = foo<int, int>; // #1
>>>> template<class T> struct foo<T, void> { }; // #2
>>>> template<> struct foo<void, void> { }; // #3
>>>>
>>>> #1 is a *specialization* of the class template foo. It is
>>>> *instantiated* when you construct one or depend on its size, or its
>>>> members.
>>>> #2 is a *partial specialization* and #3 is an explicit specialization.
>>>> But #1 is a speclialization, not an instantiation.
>>>>
>>>> Instantiation is a process that happens during compilation. A
>>>> specialization is a type (or function, or variable) generated from a
>>>> template by substituting arguments for the template parameters. The
>>>> python type printer matches specializations.
>>> Lesson learned, thanks.
>>>
>>> Maybe comment on line 169 is wrong then. I think there is a clue in the
>>> function name 'is_specialization_of' :-)
>> Good point! Thanks, I'll fix it.
>>
>>>>> -    def __init__(self, match, name):
>>>>> -        self.match = match
>>>>> +    def __init__(self, template, name, targ1):
>>>> Is there a reason to require targ1 here, instead of making it
>>>> optional, by using =None as the default?
>>> In your original, and I know untested, proposal it was not working.
>>>
>>> The function add_one_type_printer was missing to pass its targ1
>>> parameter to the FilteringTypePrinter ctor but thanks to the default
>>> value it was un-noticed by the interpreter.
>> My untested patch had this, which adds it, doesn't it?
>>
>> -def add_one_type_printer(obj, match, name):
>> -    printer = FilteringTypePrinter('std::' + match, 'std::' + name)
>> +def add_one_type_printer(obj, match, name, targ1 = None):
>> +    printer = FilteringTypePrinter('std::' + match, 'std::' + name, targ1)
>>       gdb.types.register_type_printer(obj, printer)
>>       if _versioned_namespace:
>>           ns = 'std::' + _versioned_namespace
>> -        printer = FilteringTypePrinter(ns + match, ns + name)
>> +        printer = FilteringTypePrinter(ns + match, ns + name, targ1)
>>           gdb.types.register_type_printer(obj, printer)
Indeed, I guess I mess it up myself when doing all my tests.
>>
>>
>> I think FilteringTypePrinter should be usable without specifying None
>> explicitly as the argument. Even if we don't actually use it that way
>> today, it seems like a better API. If the argument is optional, then
>> the idiomatic way to express that is to give it a default, not require
>> None to be passed.
>>
>> I'll add that default argument, but first I need to figure out why I'm
>> seeing new failures for libfundts.cc with -D_GLIBCXX_USE_CXX11_ABI=0.
>> Your patch has introduced this new error:
>>
>> $12 = Python Exception <class 'gdb.error'>: No type named
>> std::experimental::fundamentals_v1::any::_Manager_internal<std::__cxx11::basic_string<char,
>> std::char_traits<char>, std::allocator<char> >>.
>> got: $12 = Python Exception <class 'gdb.error'>: No type named
>> std::experimental::fundamentals_v1::any::_Manager_internal<std::__cxx11::basic_string<char,
>> std::char_traits<char>, std::allocator<char> >>.
>> FAIL: libstdc++-prettyprinters/libfundts.cc print as
> The problem happens here in StdExpAnyPrinter:
>
>              mgrname = m.group(1)
>              # FIXME need to expand 'std::string' so that gdb.lookup_type works
>              if 'std::string' in mgrname:
>                  mgrname = re.sub("std::string(?!\w)",
> str(gdb.lookup_type('std::string').strip_typedefs()), m.group(1))
>
>              mgrtype = gdb.lookup_type(mgrname)
>
> After your patch, gdb.lookup_type('std::string').strip_typedefs() is
> returning std::__cxx11::basic_string<char,...> which is not the
> correct type for this specialization of the any manager function. It
> contains a std::basic_string<char,...>.
>
I had noticed this usage of std::string but surprisingly had never 
managed to have a test failure because of that so I left it untouch.

Note that I had not re-tested the patch after your approval, maybe 
something changed in the month gap.

Thanks for having sorted that out.