Re: [PATCH 1/3] Introduce gdb::unique_ptr

[Luis Machado <lgustavo@codesourcery.com>]

On 10/11/2016 11:24 AM, Pedro Alves wrote:
> On 10/11/2016 04:16 PM, Eli Zaretskii wrote:
>
>> IMO, requiring to build GCC as a prerequisite for building GDB is a
>> major setback.  Building GDB is a relatively easy and straightforward
>> task today, even a native MS-Windows build.  By contrast, building GCC
>> requires quite a few additional prerequisites, which will also need to
>> be built correctly.  It also requires to configure the GCC being built
>> itself, which involves considering a large number of opt-in and
>> opt-out features, whose descriptions are not well suited for casual
>> users, and therefore whose consequences cannot be easily understood.
>
> Windows may be one of the hardest systems on which to build GCC.
> For Unix systems, it's relatively painless.  It's easy to find scripts
> around the web that download the necessary dependencies and build gcc,
> all in one go.  I think the GCC source tree has contrib patches for
> at least the downloading part.
>
>> Yes, I use GCC, of course, but I just upgraded to 5.3.0 here a few
>> months ago, while you seem to be already talking about 6.x.  If we
>> start on this slippery slope, I can easily envision the requirement to
>> go up to 7.x very soon, exactly like switching to C++-compatible GDB
>> caused, within just few months,
>
> That's a misunderstanding.  Full C++11 support is available
> in gcc 4.8 already.  I believe it's easy to find binary mingw
> gcc's of (at least) that vintage easily, for both mingw and mingw-64.
>
> mingw talks about gcc 4.8 binaries here:
>
>  http://www.mingw.org/wiki/howto_install_the_mingw_gcc_compiler_suite
>
> I don't expect anyone to _have_ to build any mingw compiler to be able
> to build gdb for mingw.
>
> It's just that gcc 6.x is the first version that has switched
> the _default_ mode for C++ to -std=gnu++14.  So until someone writes a
> patch that make gdb's build system enable C++11 support with gcc < 6,
> then the C++11-only code in the gdb::unique_ptr patch that I'm proposing
> will only be active with gcc 6.1 onward.  But really I'm not
> proposing to _require_ 6.x at all.
>
>> a massive rewrite of GDB in complex C++.
>
> Most of the changes have been around using std::string, destructors,
> and RAII, which are basic everyday C++ things.  The latter two are
> mainly about using compiler support for things we have to manually
> today (make_cleanup).   std::string just makes code shorter and safer,
> I don't see a real downside or anything complex about it.
>
> A few patches that build supporting widgets will naturally use a
> bit more complex C++ internally, all in the name of making _users_ of
> such widgets significantly simpler.  This patch is one such example.
> These kinds of support patches naturally will need to come
> before we can make use of the features they add support for, so
> while it may appear we're going to keep adding lots of magic
> things, I don't think that's true.

Maybe this should be discussed in gdb@, but...

Some of Eli's points resonate with me. It seems we just recently got the 
C++ compatibility sorted out and we're quickly moving on to try and 
C++-ify what we can with no clear goal, priority list or high level 
picture. So, just to make it C++ now that we require a C++ compiler.

I thought i'd throw this question out there. Wasn't the goal of moving 
to C++ to help the implementation of features that were hard to 
implement with C like some of the Fortran bits with dynamic arrays? Also 
improve the poor experience with C++ debugging?

I was asking myself, this week, if GCC went through such a big 
C++-ification effort when they moved away from C.

Another point i worry about is that we will switch the focus, at least 
for a few months, to C++-ifying things "just because" instead of taking 
the opportunity of such a big change to review bits of GDB that need to 
be redesigned/dropped/go away. Maybe just converting existing things to 
C++ is not the right answer, even though it is fun to do and will 
provide enough hacking fun?

I have another point about whether this will stimulate more contributors 
to send patches to GDB or not, but that's enough rambling for now. :-)