Re: [PATCH] [gdb/build] Fix build breaker with -std=c++11

[Tom de Vries <tdevries@suse.de>]

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On 8/7/23 20:01, John Baldwin wrote:
> On 8/7/23 10:15 AM, Tom de Vries via Gdb-patches wrote:
>> On 8/7/23 16:35, Simon Marchi wrote:
>>>
>>>
>>> On August 6, 2023 7:59:15 p.m. EDT, Tom de Vries via Gdb-patches 
>>> <gdb-patches@sourceware.org> wrote:
>>>> When building with -std=c++11 I run into:
>>>> ...
>>>> gdb/dwarf2/cooked-index.c: In member function \
>>>>    ‘void cooked_index::start_writing_index(dwarf2_per_bfd*)’:
>>>> gdb/dwarf2/cooked-index.c:469:10: error: lambda capture initializers 
>>>> only \
>>>>    available with -std=c++14 or -std=gnu++14 [-Werror]
>>>>            ctx = std::move (ctx)] ()
>>>>            ^~~
>>>> ...
>>>>
>>>> Fix this by capturing a copy instead:
>>>> ...
>>>>      = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd, 
>>>> ctx] ()
>>>> ...
>>>>
>>>> Tested on x86_64-linux.
>>>>
>>>> Reported-By: Tom Tromey <tom@tromey.com>
>>>
>>> When we encounter things like this, should we add some greppable TODO 
>>> comment to record an actionable item for when we switch to a more 
>>> recent C++ version?
>>
>> Hi Simon,
>>
>> thanks for the review.
>>
>> Fine by me, added comment.
> 
> An alternative that is slightly more work but might be nicer long term 
> would be
> to #if on the C++ version, so for example:
> 
> #if __cplusplus >= 201402L
>    = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd,
>                                                  ctx = std::move (ctx)] ()
> #else
>    = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd, ctx]) ()
> #endif
> 

Thanks for the suggestion.  Updated patch attached.

Thanks,
- Tom

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From ddbe8c3c8a8665e77f9ebb108c5627a6ebecb81f Mon Sep 17 00:00:00 2001
From: Tom de Vries <tdevries@suse.de>
Date: Mon, 7 Aug 2023 00:31:04 +0200
Subject: [PATCH] [gdb/build] Fix build breaker with -std=c++11
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When building with -std=c++11 I run into:
...
gdb/dwarf2/cooked-index.c: In member function \
  ‘void cooked_index::start_writing_index(dwarf2_per_bfd*)’:
gdb/dwarf2/cooked-index.c:469:10: error: lambda capture initializers only \
  available with -std=c++14 or -std=gnu++14 [-Werror]
          ctx = std::move (ctx)] ()
          ^~~
...

Fix this by capturing a copy instead when using -std=c++11:
...
    = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd, ctx] ()
...

Tested by building with and without -stdc=++11 on x86_64-linux.

Reported-By: Tom Tromey <tom@tromey.com>
---
 gdb/dwarf2/cooked-index.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index df82e86b690..92ef0e35c5e 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -466,7 +466,12 @@ cooked_index::start_writing_index (dwarf2_per_bfd *per_bfd)
      started, because it may call 'wait'.  */
   m_write_future
     = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd,
-						   ctx = std::move (ctx)] ()
+#if __cplusplus >= 201402L
+						   ctx = std::move (ctx)
+#else
+						   ctx
+#endif
+						   ] ()
 	{
 	  maybe_write_index (per_bfd, ctx);
 	});

base-commit: 8d27b09d0877982dc2252c01a3f1d9c631b2d6eb
-- 
2.35.3