[cfe-dev] Getting the FieldDecl from a CXXDependentScopeMemberExpr

[Adrien Chauve]

On Thu, Jun 23, 2011 at 19:42, Douglas Gregor <dgregor at apple.com> wrote:
>
> On Jun 23, 2011, at 10:10 AM, Adrien Chauve wrote:
>
>> On Thu, Jun 23, 2011 at 17:24, Douglas Gregor <dgregor at apple.com> wrote:
>>>
>>> On Jun 22, 2011, at 11:49 PM, Adrien Chauve wrote:
>>>
>>>> On Wed, Jun 22, 2011 at 20:26, Douglas Gregor <dgregor at apple.com> wrote:
>>>>>
>>>>> On Jun 22, 2011, at 10:05 AM, Adrien Chauve wrote:
>>>>>
>>>>>> Thanks a lot!
>>>>>>
>>>>>> If I understand well, the AST is of little help for dependent names
>>>>>> inside template classes.
>>>>>
>>>>> Correct. The language is of little help here, either, since it's a fundamental part of the C++ template model.
>>>>>
>>>>>> Is there any tool to deal with it? Without instanciation, can we do
>>>>>> anything with class templates?
>>>>>
>>>>>
>>>>> Not really. You could guess by looking into the primary templates, but the answers you get will be wrong if any specializations come along, and you may not even be able to get enough type information to determine which primary template to look in.
>>>>>
>>>>>        - Doug
>>>>>
>>>>
>>>> Thanks!
>>>>
>>>> By any chance, would it be possible to try and instantiate a primary
>>>> template with a list of dumb template parameter types (say ints), skip
>>>> it if it fails, and if there is no specialization and the instatiation
>>>> succeeds, draw some conclusions on the primary template?
>>>
>>>
>>> There's no infrastructure for doing this, but it should be possible. However, I don't think you'd want to instantiate with ints… rather, you'd want to instantiate with some dummy type that doesn't imply any specific behavior.
>>>
>>> However, it depends on your goals. It might just be easier to inspect the contents of the primary template directly, since there's a full AST there anyway.
>>>
>>>        - Doug
>>
>>
>> My goals are very simple for now: I would like to have a tool to
>> rename all fields contained in the source code of a given project
>> (then of course classes, functions, etc...) according to the naming
>> conventions chosen for the project.
>
> I wish C++ allowed this to be simple :)

Yes at least the goals are simple to describe ;) but indeed not to implement.

>
>> For instance, I would like to rename:
>>
>>    template<typename T>
>>    struct Foo
>>    {
>>        std::pair<T,T> bar;
>>
>>        void set(T x, T y)
>>        {
>>            bar.first = x;
>>            bar.second = y;
>>        }
>>    };
>>
>> into:
>>
>>    template<typename T>
>>    struct Foo
>>    {
>>        std::pair<T,T> m_bar;  // bar -> m_bar
>>
>>        void set(T x, T y)
>>        {
>>            m_bar.first = x;   // bar -> m_bar but not first -> m_first
>>            m_bar.second = y;
>>        }
>>    };
>>
>>
>> I use VisitCXXDependentScopeMemberExpr but from that I get only the
>> name of the member and its location.
>
> Right.
>
>> As std::pair<T,T> is a dependent name, I can't get access to its
>> primary class template, whose location is not inside the project root
>> directory so, of course, I don't want to rename its fields "first" and
>> "second", but I do want to rename "bar".
>>
>> Is there a way to get this kind of information using the AST of the
>> primary template Foo without instantiating it?
>
> In this case, it's likely that m_bar will have the type pair<T, T>, which will be a ClassTemplateSpecializationType. You could look at the ClassTemplateDecl (pair) and its primary template definition (a CXXRecordDecl) to lookup the name.

Yes indeed in this case we get a MemberExpr so we're saved.

The problem arises in this case:

   template<typename T>
   struct Foo
   {
       std::pair<T,T> bar;

       void setFromOther(const Foo<T>& other)
       {
           bar.first = other.bar.first;
       }
   };

Here I have a lot of info on "this->bar" but nearly nothing on "other".

>
> Alternatively, you could look at the actual instantiations of this set() function and see what fields that actually refer to.

Yes (if the function is actually used in the project, but sure if it's
not it's another problem). I think I understand how to get from an
instanciation to the primary template, but what about finding all the
instantiations of a given primary template? Are there some kind of
links in the AST?

Another problem comes if, even if all the functions of the primary
template are used in the project, they are not all used in the same
translation unit.

>> Another piece of information I would need is to know if a given
>> CXXDependentScopeMemberExpr refers to a field or a method. This
>> information lies in the AST since if the parent expression is a
>> CallExpr it's a method, otherwise it's a field.
>
> Unfortunately, that's not always true. You could have a call to a field whose type has an overloaded operator() or is a function pointer.

Yes indeed.

>> But I'm not sure there
>> is a simple way to get the parent of a given expr (I only saw
>> iterators on children expr), otherwise I suppose you have to hack the
>> traversal of the AST and store some information on the traversed
>> nodes.
>
>
> We don't encode that information directly in the AST, although you can get that information using the ParentMap structure in clang/AST/ParentMap.h.

I'm going to look at that, thanks.

>        - Doug


Thanks,
Adrien