Re: [PATCH v3 06/17] Replace delete_longjmp_breakpoint_cleanup with a forward_scope_exit type

[John Baldwin <jhb@FreeBSD.org>]

On 1/24/19 9:09 AM, Pedro Alves wrote:
> On 01/24/2019 11:23 AM, Pavel I. Kryukov wrote:
>> The patch causes build errors on XCode:
>>
>> $ clang --version
>> Apple LLVM version 10.0.0 (clang-1000.11.45.5)
>> Target: x86_64-apple-darwin17.7.0
>> Thread model: posix
>> InstalledDir: /Applications/Xcode10.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
> 
> Thanks.
> 
> Hmm, I only have clang 5.0.2 handy, and I think it links with
> libstdc++ instead of clang's own libc++.  Here it builds fine.
> I had also made sure the patch builds fine with g++ 4.8.
> 
>>
>>
>> In file included from breakpoint.c:34:
>> In file included from ./inferior.h:54:
>> ./common/forward-scope-exit.h:98:7: error: no matching constructor for
>> initialization of 'decltype(std::bind(&delete_longjmp_breakpoint,
>> std::declval<int>()))' (aka '__bind<void (*)(int), int>')
>>     : m_bind_function (std::bind (function, args...))
>>       ^                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> ./common/gdb_optional.h:155:19: note: in instantiation of member
>> function 'detail::forward_scope_exit<void (int),
>> &delete_longjmp_breakpoint, void (int)>::forward_scope_exit' requested
>> here
>>     new (&m_item) T (std::forward<Args>(args)...);
>>                   ^
>> breakpoint.c:11127:18: note: in instantiation of function template
>> specialization 'gdb::optional<detail::forward_scope_exit<void (int),
>> &delete_longjmp_breakpoint, void (int)> >::emplace<int &>' requested
>> here
>>       lj_deleter.emplace (thread);
>>                  ^
>> /Applications/Xcode-10.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/functional:2220:7:
>> note: candidate constructor (the implicit copy constructor) not
>> viable: no known conversion from '__bind<[...], int &>' to 'const
>> __bind<[...], int>' for 1st argument
>> class __bind
>>       ^
> 
> Hmm, references to the copy ctor.  I don't really know why I ended up
> with a copy here.  We can just pass the arguments directly to the
> being-constructed bind.  Does this work for you?
> 
> From b1caeb9c5334a59680af7b7717ab620e5a912bcf Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Thu, 24 Jan 2019 16:25:44 +0000
> Subject: [PATCH] No copy ctor
> 
> ---
>  gdb/common/forward-scope-exit.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/gdb/common/forward-scope-exit.h b/gdb/common/forward-scope-exit.h
> index 8d639151a4..bffc6e683b 100644
> --- a/gdb/common/forward-scope-exit.h
> +++ b/gdb/common/forward-scope-exit.h
> @@ -95,7 +95,7 @@ class forward_scope_exit<Function, function, Res (Args...)>
>  
>  public:
>    explicit forward_scope_exit (Args ...args)
> -    : m_bind_function (std::bind (function, args...))
> +    : m_bind_function (function, args...)
>    {
>      /* Nothing.  */
>    }
> 

I got the same failure on FreeBSD (also uses libc++) and this patch fixed
the build for me.

-- 
John Baldwin