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

Gregory Szorc gregory.szorc at gmail.com
Tue May 15 12:40:41 PDT 2012

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.

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