[cfe-commits] [PATCH 1/4] [clang.py] Store reference to TranslationUnit in Cursor and Type

[Manuel Klimek]

On Tue, May 15, 2012 at 9:40 PM, Gregory Szorc <gregory.szorc at gmail.com> wrote:
> On Tue, May 15, 2012 at 12:31 PM, Manuel Klimek <klimek at google.com> wrote:
>> On Mon, May 14, 2012 at 10:15 AM, Manuel Klimek <klimek at google.com> wrote:
>>> On Mon, May 14, 2012 at 5:46 AM, Gregory Szorc <gregory.szorc at gmail.com>
>>> wrote:
>>>>
>>>> On 5/13/12 1:00 AM, Manuel Klimek wrote:
>>>>>
>>>>> +    @property
>>>>> +    def translation_unit(self):
>>>>> +        """Returns the TranslationUnit to which this Cursor belongs."""
>>>>> +        return getattr(self, '_tu', None)
>>>>>
>>>>> What's the reason for the default value? Do we expect that people create
>>>>> cursers via the lowlevel calls? Why would just return tu_ not work?
>>>>
>>>> Just defensive programming. If you return self._tu, that may raise an
>>>> AttributeError if _tu is not set. Theoretically, the API should ensure that
>>>> a TU is defined on all Cursor instances, so maybe an AttributeError would be
>>>> acceptable.
>>>
>>>
>>> I'd prefer that - to me defensive programming means to:
>>> 1. never crash for invalid user input
>>> 2. crash hard if there's an actual bug in the library
>>>
>>> If the cursor should never be generated by a user (-> the contract of the
>>> library is to not break that), I think we should use _tu and have the
>>> AttributeError thrown if it's not there. Or I'm also fine with putting in an
>>> assert that checks that the attribute is there and delivers a nicer error in
>>> case it's missing.
>>>
>>>>>
>>>>> +        # Store a reference to the TU in the Python object so it won't
>>>>> get GC'd
>>>>> +        # before the Cursor.
>>>>> +        tu = None
>>>>> +        for arg in args:
>>>>> +            if isinstance(arg, TranslationUnit):
>>>>> +                tu = arg
>>>>> +                break
>>>>> +
>>>>> +            if hasattr(arg, 'translation_unit'):
>>>>> +                tu = arg.translation_unit
>>>>> +                break
>>>>> +
>>>>> +        assert tu is not None
>>>>> +
>>>>> +        res._tu = tu
>>>>>
>>>>> That seems - odd. I can't find docs what from_result is supposed to do,
>>>>> or what "args" are provided. But having to search through them for a TU
>>>>> seems wrong - shouldn't they all have a TU?
>>>>
>>>> from_result is the errcheck function for the ctypes functions that return
>>>> a Cursor. The 3rd argument to an errcheck function are the original
>>>> arguments passed into the called function.  For many of the functions, the
>>>> original argument is a Cursor. However, clang_getTypeDeclaration takes a
>>>> Type and clang_getTranslationUnitCursor receives a TranslationUnit.
>>>>
>>>> It is true that all of the functions today receive a single argument, so
>>>> the iteration isn't required. However, that may change with the addition of
>>>> new APIs in the future (this is how I coded it in my nearly feature-complete
>>>> branch, so I'm guessing it is actually required from a future patch).
>>>
>>>
>>> The question is: don't we just want to assert that all of those have a TU
>>> (or are a TU)?
>>
>> ^ this question is still open I think...
>
> I don't think it is. Both modified from_result functions now assert if
> a TU could not be found.
>
> Or, are you asking for something more? In the future, every live
> object will likely hold a reference to a TU. We aren't there quite
> yet. But, this patch is a step in the right direction.

Ah, ok, that was my question - why not every object has a TU and we
can assert *for every object* that it has a TU. If that's a follow-up
step, then LGTM.

Cheers,
/Manuel