llvm dev - Sep 2013 - [LLVMdev] extern "C" and namespaces

Can someone confirm whether the following is a known clang bug? I am having a
lot of trouble compiling some old legacy code due to this error. I know
"using namespace" is horrible but that doesn't make it illegal
(g++ accepts this). The fix is easy but there are just too many instances of
this in the legacy code. The following is not from the code I am trying to
compile but is derived from an example in the C++11 standard (7.3.4 note 6)

foo.cpp:
namespace A {
    extern "C" int g();
    extern "C++" int h();
}
namespace B {
    extern "C" int g();
    extern "C++" int h(int);
}
using namespace A;
using namespace B;
void f() {
    g(); // okay: name g refers to the same entity
    h(); // okay: overload resolution selects A::h
}

foo.cpp:12:5: error: call to 'g' is ambiguous
    g(); // okay: name g refers to the same entity
    ^
foo.cpp:2:20: note: candidate function
    extern "C" int g();
                   ^
foo.cpp:6:20: note: candidate function
    extern "C" int g();
                   ^
1 error generated.
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On Thu, Sep 19, 2013 at 11:50:52PM +0000, Riyaz Puthiyapurayil
wrote:
> Can someone confirm whether the following is a known clang bug?
I don't think it is a clang bug. If you really want to force both instances
of g to refer to the same function, use asm("g") for one of them.
"g++
accepts it" is not a very good measurement for whether something is
legal or sensible.

Joerg

On Thu, Sep 19, 2013 at 11:50:52PM +0000, Riyaz Puthiyapurayil
wrote:
> Can someone confirm whether the following is a known clang bug? I am having
a lot of trouble compiling some old legacy code due to this error. I know
"using namespace" is horrible but that doesn't make it illegal
(g++ accepts this). The fix is easy but there are just too many instances of
this in the legacy code. The following is not from the code I am trying to
compile but is derived from an example in the C++11 standard (7.3.4 note 6)
> 
> foo.cpp:
> namespace A {
>     extern "C" int g();
>     extern "C++" int h();
> }
> namespace B {
>     extern "C" int g();
>     extern "C++" int h(int);
> }
> using namespace A;
> using namespace B;
> void f() {
>     g(); // okay: name g refers to the same entity
>     h(); // okay: overload resolution selects A::h
> }
> 
> foo.cpp:12:5: error: call to 'g' is ambiguous
>     g(); // okay: name g refers to the same entity
>     ^
> foo.cpp:2:20: note: candidate function
>     extern "C" int g();
>                    ^
> foo.cpp:6:20: note: candidate function
>     extern "C" int g();
>                    ^
> 1 error generated.
--- end quoted text ---

Hi Riyaz,
Based on the example in the C++11 standard at 7.3.4 note 6, which you have
literally
cut and pasted as your example, it has to be a bug for c++11. The standard
asserts
"okay: name g refers to the same entity". It's valid code.

enjoy,
Karen
-- 
Karen Shaeffer                 Be aware: If you see an obstacle in your path,
Neuralscape Services           that obstacle is your path.        Zen proverb

On 19 September 2013 16:50, Riyaz Puthiyapurayil <
Riyaz.Puthiyapurayil at synopsys.com> wrote:
>  Can someone confirm whether the following is a known clang bug?
>
Yes, this was just fixed, literally minutes ago in r191064.

Nick

> I am having a lot of trouble compiling some old legacy code due to this
> error. I know “using namespace” is horrible but that doesn’t make it
> illegal (g++ accepts this). The fix is easy but there are just too many
> instances of this in the legacy code. The following is not from the code I
> am trying to compile but is derived from an example in the C++11 standard
> (7.3.4 note 6)****
>
> ** **
>
> *foo.cpp:*
>
> namespace A {****
>
>     extern "C" int g();****
>
>     extern "C++" int h();****
>
> }****
>
> namespace B {****
>
>     extern "C" int g();****
>
>     extern "C++" int h(int);****
>
> }****
>
> using namespace A;****
>
> using namespace B;****
>
> void f() {****
>
>     g(); // okay: name g refers to the same entity****
>
>     h(); // okay: overload resolution selects A::h****
>
> }****
>
> ** **
>
> foo.cpp:12:5: error: call to 'g' is ambiguous****
>
>     g(); // okay: name g refers to the same entity****
>
>     ^****
>
> foo.cpp:2:20: note: candidate function****
>
>     extern "C" int g();****
>
>                    ^****
>
> foo.cpp:6:20: note: candidate function****
>
>     extern "C" int g();****
>
>                    ^****
>
> 1 error generated.****
>
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