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

Manuel Klimek klimek at google.com
Tue May 15 12:55:04 PDT 2012

On Tue, May 15, 2012 at 9:52 PM, Gregory Szorc <gregory.szorc at gmail.com> wrote:
> On Tue, May 15, 2012 at 12:45 PM, Manuel Klimek <klimek at google.com> wrote:
>> 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.
> Well, in the case of from_result (or any errcheck function), not every
> argument to the original function may have a TU attached. e.g. integer
> arguments.

So that means we cannot even be sure that we'll always find a TU?
Still trying to understand from_result better.


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