Hi!
> Le 20 janv. 2019 à 16:02, Derek Clegg <de...@me.com> a écrit :
>
> Hi, Akim —
>
> On Jan 19, 2019, at 11:49 PM, Akim Demaille <a...@lrde.epita.fr> wrote:
>>
>> I don't think I will address this warning, the cure is way worse than the
>> problem.
>>
>> To add the destructor, I must make the signature explicit, and it cannot be
>> different from the one in the base class, so I must add noexcept:
>>
>> ~syntax_error () YY_NOEXCEPT;
>
> In C++98 the signature is
> virtual ~exception() throw();
> and in C++11 the signature is
> virtual ~exception();
> so this only has to be handled specially for C++98.
Wow... You are right! I would never have believed they actually removed the
'throw()', instead of making it 'noexcept'...
This is what I have in my copy of the C++98 standard:
> 18.6.1 Class exception [lib.exception]
>
> namespace std {
> class exception {
> public:
>
> exception() throw();
> exception(const exception&) throw();
> exception& operator=(const exception&) throw();
> virtual ~exception() throw();
> virtual const char* what() const throw();
>
> }; }
and this is n3797, a draft of C++14. I guess they did the same for C++11.
> 18.8.1 Class exception [exception]
>
> namespace std {
> class exception {
> public:
>
> exception() noexcept;
> exception(const exception&) noexcept;
> exception& operator=(const exception&) noexcept;
> virtual ~exception();
> virtual const char* what() const noexcept;
>
> }; }
The reason I did not even try is that I fell onto this in libc++ while
addressing your bug report:
In comment:
> class exception
> {
> public:
> exception() noexcept;
> exception(const exception&) noexcept;
> exception& operator=(const exception&) noexcept;
> virtual ~exception() noexcept;
> virtual const char* what() const noexcept;
> };
Or actual code:
> class _LIBCPP_EXCEPTION_ABI runtime_error
> : public exception
> {
> private:
> _VSTD::__libcpp_refstring __imp_;
> public:
> explicit runtime_error(const string&);
> explicit runtime_error(const char*);
>
> runtime_error(const runtime_error&) _NOEXCEPT;
> runtime_error& operator=(const runtime_error&) _NOEXCEPT;
>
> virtual ~runtime_error() _NOEXCEPT;
>
> virtual const char* what() const _NOEXCEPT;
> };
with
> #ifndef _LIBCPP_HAS_NO_NOEXCEPT
> # define _NOEXCEPT noexcept
> # define _NOEXCEPT_(x) noexcept(x)
> #else
> # define _NOEXCEPT throw()
> # define _NOEXCEPT_(x)
> #endif
Besides, cppreference shows nothing about exception specifiers
(https://en.cppreference.com/w/cpp/error/exception/%7Eexception).
> Wouldn’t it be sufficient to explicitly write
>
> #if 201103L <= YY_CPLUSPLUS
> ~syntax_error();
> #else
> ~syntax_error() throw();
> #endif
>
> and similarly for the definition?
Yes, it does. Actually, all this is a red-herring, ~syntax_error works fine
with throw() and noexcept. It's the other uses of YY_NOEXCEPT as throw() that
is a problem. I don't feel like investigating right now, but I should do it at
some point.
> It seems problematic to redefine YY_NOEXCEPT, especially since “noexcept” and
> “throw()” aren’t used equivalently.
Well, I thought it was the case where I used it.
I will install the following commit when it's validated by the CI. It depends
on another commit (glr.cc: be more alike lalr1.cc). You can fetch it from my
branch Wweak-vtables on GitHub.
Again, thanks a lot Derek!
commit 9d792e20f4e3b03226095d9b3389038bf6c14791
Author: Akim Demaille <akim.demai...@gmail.com>
Date: Sun Jan 20 08:23:41 2019 +0100
c++: address -Wweak-vtables warnings
Reported by Derek Clegg
http://lists.gnu.org/archive/html/bug-bison/2019-01/msg00021.html
To avoid this warning, we need syntax_error to have a virtual function
defined in a compilation unit. Let it be the destructor. To comply
with C++98, this dtor should be 'throw()'. Merely making YY_NOEXCEPT
be 'throw()' in C++98 triggers
errors (http://lists.gnu.org/archive/html/bug-bison/2019-01/msg00022.html),
so let's introduce YY_NOTHROW and flag only ~syntax_error with it.
Also, since we add an explicit dtor, we now need to provide an
explicit copy ctor.
* configure.ac (warn_cxx): Add -Wweak-vtables.
* data/skeletons/c++.m4 (YY_NOTHROW): New.
(syntax_error): Declare the dtor, and define the copy ctor.
* data/skeletons/glr.cc, data/skeletons/lalr1.cc (~syntax_error):
Define.
diff --git a/configure.ac b/configure.ac
index a3a471af..1b5343e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -100,7 +100,7 @@ if test "$enable_gcc_warnings" = yes; then
-Wpointer-arith -Wshadow
-Wwrite-strings'
warn_c='-Wbad-function-cast -Wstrict-prototypes'
- warn_cxx='-Wextra-semi -Wnoexcept -Wundefined-func-template'
+ warn_cxx='-Wextra-semi -Wnoexcept -Wundefined-func-template -Wweak-vtables'
# Warnings for the test suite only.
#
# -fno-color-diagnostics: Clang's use of colors in the error
diff --git a/data/skeletons/c++.m4 b/data/skeletons/c++.m4
index f6f95c4c..acc35b62 100644
--- a/data/skeletons/c++.m4
+++ b/data/skeletons/c++.m4
@@ -77,8 +77,10 @@ m4_define([b4_cxx_portability],
// Support noexcept when possible.
#if 201103L <= YY_CPLUSPLUS
# define YY_NOEXCEPT noexcept
+# define YY_NOTHROW
#else
# define YY_NOEXCEPT
+# define YY_NOTHROW throw ()
#endif
// Support noexcept when possible.
@@ -217,7 +219,14 @@ m4_define([b4_public_types_declare],
syntax_error (]b4_locations_if([const location_type& l, ])[const
std::string& m)
: std::runtime_error (m)]b4_locations_if([
, location (l)])[
- {}]b4_locations_if([
+ {}
+
+ syntax_error (const syntax_error& s)
+ : std::runtime_error (s.what ())]b4_locations_if([
+ , location (s.location)])[
+ {}
+
+ ~syntax_error () YY_NOEXCEPT YY_NOTHROW;]b4_locations_if([
location_type location;])[
};
diff --git a/data/skeletons/glr.cc b/data/skeletons/glr.cc
index 778c65b8..56217341 100644
--- a/data/skeletons/glr.cc
+++ b/data/skeletons/glr.cc
@@ -160,6 +160,9 @@ m4_pushdef([b4_parse_param],
m4_defn([b4_parse_param_orig]))dnl
]b4_parser_class::~b4_parser_class[ ()
{}
+ ]b4_parser_class[::syntax_error::~syntax_error () YY_NOEXCEPT YY_NOTHROW
+ {}
+
int
]b4_parser_class[::operator() ()
{
diff --git a/data/skeletons/lalr1.cc b/data/skeletons/lalr1.cc
index 053ba3be..1dc2851d 100644
--- a/data/skeletons/lalr1.cc
+++ b/data/skeletons/lalr1.cc
@@ -562,6 +562,8 @@ m4_if(b4_prefix, [yy], [],
]b4_parser_class::~b4_parser_class[ ()
{}
+ ]b4_parser_class[::syntax_error::~syntax_error () YY_NOEXCEPT YY_NOTHROW
+ {}
/*---------------.
| Symbol types. |
