[PATCH] PR19095 Undefined reference to friend template function defined inside template class

[suyog sarda]

Hi Richard,

Thanks for the review. I Agree to your explaination. Following are the
points what i understood :

1. setInstantiatedFromMemberTemplate call should not be skipped since it
causes mix up of  template parameter list numbering and wrong
substitutions,
    which is clearly visible in the test case as well.
2. When C is instantiated twice, it should throw re-definition error of
function f, which is not done (with or without my patch).
3. In the same function call 'TemplateDeclInstantiator::VisitFunctionDecl',
there is a check 'if (isFriend)'.
    There is a standard described '[temp.friend] p4 (DR329)' inside that
check, which checks if the *FunctionDecl D *is Declared as well as Defined
(isThisDeclarationADefintion).
    In my opinion, at this point the function defintion is not being set
for friend function defined inside the class template.
4. While debugging, it is seen that, the *FunctionDecl D *is *defined *holds
true but '*Function->isDefined(Definition)*' evaluates to false (I did not
get why it evaluates to false),                 because of which
re-defintion error is not emitted.

There is a similar bug for operator overloading - Bug 14785. There also
same case is happening - not able to identify if friend function (in 14785
its operator overloading function) is defined inside class template.

Can you please help me out if my above analysis is correct as well as
indicate where/how to set the definition of the declared function? Your
help is highly appreciated.



On Sat, Apr 12, 2014 at 1:57 AM, Richard Smith <richard at metafoo.co.uk>wrote:

> Hi!
>
> I'm afraid this patch is incorrect; it even does the wrong thing in your
> test case. Skipping the setInstantiatedFromMemberTemplate call causes us to
> mix up the template parameter list numbering -- we substitute the argument
> given for T as the value U, and we don't substitute anything for T. For
> instance, in the definition of f instantiated for the f(3.0) call, we
> should have T=double, U=int, but we actually have T=<no value>, U=double,
> as can be seen in the AST dump.
>
> This also does the wrong thing if C is instantiated twice -- such a case
> should be an error, because f would have multiple definitions.
>
>
> On Mon, Mar 24, 2014 at 5:29 AM, suyog sarda <sardask01 at gmail.com> wrote:
>
>> Gentle Ping!!
>>
>>
>> On Thu, Mar 20, 2014 at 9:46 AM, suyog sarda <sardask01 at gmail.com> wrote:
>>
>>> Gentle Ping!!
>>>
>>>
>>> On Fri, Mar 14, 2014 at 10:29 PM, suyog sarda <sardask01 at gmail.com>wrote:
>>>
>>>> Hi,
>>>>
>>>> Attaching patch for bug 19095. Please help in reviewing the same.
>>>>
>>>> Also, I haven't attached a test case yet in the patch as i am not sure
>>>> how it should be and in which file it should be.
>>>>
>>>> In my opinion, the test case would go into *tools/clang/test/SemaCXX/friend.cpp
>>>> *would be something like below (similar to that mentioned in the bug)
>>>>
>>>>
>>>>
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>>>> * template <class T>void f(T);template <class U>class C{  template
>>>> <class T>  friend void f(T)  {     C<U> c;     c.i = 3;  }  public :
>>>> void g()      {       f(3.0); // OK     }    int i;};void h (){  f(7); //
>>>> OK  C<double> c;  c.g();}*
>>>>
>>>>
>>>> Please help in reviewing the patch as well as the test case.
>>>> --
>>>> With regards,
>>>> Suyog Sarda
>>>>
>>>
>>>
>>>
>>> --
>>> With regards,
>>> Suyog Sarda
>>>
>>
>>
>>
>> --
>> With regards,
>> Suyog Sarda
>>
>> _______________________________________________
>> cfe-commits mailing list
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>>
>>
>


-- 
With regards,
Suyog Sarda
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