Re: [PATCH] Fix gnu-versioned-namespace build

["François Dumont" <frs.dumont@gmail.com>]

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On 12/11/19 9:44 PM, Jonathan Wakely wrote:
> On 11/12/19 21:23 +0100, François Dumont wrote:
>> On 12/11/19 12:16 PM, Jonathan Wakely wrote:
>>> On 11/12/19 08:29 +0100, François Dumont wrote:
>>>> I plan to commit this tomorrow.
>>>>
>>>> Note that rather than just adding the missing 
>>>> _GLIBCXX_[BEGIN,END]_VERSION_NAMESPACE I also move anonymous 
>>>> namespace usage outside std namespace. Let me know if it was 
>>>> intentional.
>>>
>>> It was intentional, why move it?
>>
>> I just don't get the intention so I proposed to move it. But there 
>> are indeed other usages of this pattern in other src files.
>>
>> Note that in src/c++11/debug.cc I am using anonymous namespace at 
>> global scope, is that wrong ?
>
> It's certainly more fragile, so arguably it's wrong, yes.
>
> Consider:
>
> // some libc function in a system header we don't control:
> extern "C" void __foo();
>
> // libstdc++ code in a .cc file:
> namespace
> {
>  void foo() { }
> }
> namespace std
> {
>  void bar() { foo(); }
> }
>
> This fails to compile, because the name foo is ambiguous in the global
> scope. We don't control the libc headers, so we don't know all the
> names they might declare at global scope.
>
> If you don't put the unnamed namespace at global scope, the problem
> simply doesn't exist:
>
> namespace std
> {
>  namespace
>  {
>    void foo() { }
>  }
>
>  void bar() { foo(); }
> }
>
> Now it doesn't matter what names libc puts in the global scope,
> because we're never looking for foo in the global scope.
>
> It's obviously better to add our declarations to our own namespace
> that we control, not to the global namespace (and an unnamed namespace
> at global scope effectively adds the names to the global namespace).
>
>>>
>>> Adding the BEGIN/END_VERSION macros is unnecessary. Those namespaces
>>> are inline, so std::random_device already refers to
>>> std::__8::random_device when the original declaration was in the
>>> versioned namespace.
>>
>> Ok. I must confess I wasn't clear about this but looking at other src 
>> files, at least in src/c++11, was showing that it is done almost 
>> always this way, I guess we could cleanup those files.
>>
>>>
>>> The only fix needed here seems to be qualifying std::isdigit (and
>>> strictly-speaking we should also include <cctype> to declare that).
>>>
>> Like in attached patch ?
>
> Did you attach the wrong patch?
>
>
Indeed, here is the correct one.



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diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc
index 10fbe1dc4c4..04edc582b69 100644
--- a/libstdc++-v3/src/c++11/random.cc
+++ b/libstdc++-v3/src/c++11/random.cc
@@ -41,6 +41,7 @@
 
 #include <cerrno>
 #include <cstdio>
+#include <cctype> // For std::isdigit.
 
 #if defined _GLIBCXX_HAVE_UNISTD_H && defined _GLIBCXX_HAVE_FCNTL_H
 # include <unistd.h>
@@ -286,7 +287,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
     _M_mt.seed(seed);
 #else
     // Convert old default token "mt19937" or numeric seed tokens to "default".
-    if (token == "mt19937" || isdigit((unsigned char)token[0]))
+    if (token == "mt19937" || std::isdigit((unsigned char)token[0]))
       _M_init("default");
     else
       _M_init(token);