[Bug default/21843] libabigail not correctly keeping track of nested scopes for typedefs

["dodji at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=21843

dodji at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #4 from dodji at redhat dot com ---
> 1 Changed variable:
> 
>   [C]'std::vector<int, std::allocator<int> > var' was changed at test4.C:3:1:
>     type of variable changed:
>      type size hasn't changed
>      1 base class change:
>        'struct std::_Vector_base<int, std::allocator<int> >' at
> stl_vector.h:74:1 changed:
>          type size hasn't changed
>          1 data member change:
>           type of 'std::_Vector_base<int, std::allocator<int>
> >::_Vector_impl std::_Vector_base<int, std::allocator<int> >::_M_impl'
> changed:
>             type size hasn't changed
>             3 data member changes:
>              type of 'std::_Vector_base<int, std::allocator<int> >::pointer
> std::_Vector_base<int, std::allocator<int> >::_Vector_impl::_M_start'
> changed:
>                underlying type 'typedef
> __gnu_cxx::__alloc_traits<std::allocator<int> >::pointer' at
> alloc_traits.h:120:1 changed:
>                  underlying type 'typedef
> std::allocator_traits<std::allocator<int> >::pointer' at allocator.h:113:1
> changed:

[...]
           typedef name changed from
> std::allocator_traits<std::allocator<int> >::pointer to
> std::allocator<int>::pointer at allocator.h:113:1
> 

[...]

> To me this looks like:
> 1) libabigail is confused and is mistaking one type for another

Hmmh, I think it's just that libabigail is not going further enough in the
analysis.

I think there is a typedef name change, but it doesn't change the leaf
underlying type of the typedef.  In both cases, the typedef is for an 'int'. 
And that is what libabigail isn't taking into account.

So let's look at the DWARF of clang:

First, the typedef  __gnu_cxx::__alloc_traits<std::allocator<int> >::pointer is 
is represented by this DWARF:

[   8f0]        typedef
                 type                 (ref4) [   793]
                 name                 (strp) "pointer"

So the underlying type of  __gnu_cxx::__alloc_traits<std::allocator<int>
>::pointer is the type represented by the DIE 0x793.  And that DIE 0x793 is
actually std::allocator<int>::pointer, as we can see here at:

 [   74c]      class_type
               name                 (strp) "allocator<int>"
               byte_size            (data1) 1
               decl_file            (data1) 4
               decl_line            (data1) 108
[...]
 [   793]        typedef
                 type                 (ref4) [   b04]
                 name                 (strp) "pointer"

In GCC though, the typedef  __gnu_cxx::__alloc_traits<std::allocator<int>
>::pointer is is represented by this DWARF:

 [  1353]      structure_type
               name                 (strp) "__alloc_traits<std::allocator<int>
>"
               byte_size            (data1) 1
               decl_file            (data1) 16
               decl_line            (data1) 50
               sibling              (ref4) [  1454]
[...]

 [  138a]        typedef
                 name                 (strp) "pointer"
                 decl_file            (data1) 16
                 decl_line            (data1) 59
                 type                 (ref4) [   43a]


 [   410]      structure_type
               name                 (strp)
"allocator_traits<std::allocator<int> >"
               byte_size            (data1) 1
               decl_file            (data1) 4
               decl_line            (data2) 384
               sibling              (ref4) [   50b]
[...]
 [   43a]        typedef
                 name                 (strp) "pointer"
                 decl_file            (data1) 4  
                 decl_line            (data2) 392
                 type                 (ref4) [  16c6]

So in GCC, the underlying type of the typedef
__gnu_cxx::__alloc_traits<std::allocator<int> >::pointer is
"allocator_traits<std::allocator<int> >::pointer".

Note the difference in *typedef name* with clang.  With clang, the underlying
type of __gnu_cxx::__alloc_traits<std::allocator<int> >::pointer is
std::allocator<int>::pointer.

So libabigail is saying that "allocator_traits<std::allocator<int> >::pointer"
is a different typedef *name*, compared to "std::allocator<int>::pointer".

What it's failing to see is that both typedefs end up being just "int".

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