Re: [Boost-users] [filesystem] Apparent non-compliant code in current operations.hpp, ...

From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2007-10-19 05:37:11

Note for boost.devel readers: The original problem report can be found at 
http://permalink.gmane.org/gmane.comp.lib.boost.user/31028.

Currently I think the reported error is really a problem in boost code, if 
the reproducer below is indeed correct. But I'm still puzzled why cxx in 
strict ansi mode isn't complaining.

Did anyone encounter this problem already?

Note to original poster: See below for answers.

Marty Fried wrote:
> Back on Thu, 18 Oct 2007 09:53:36 +0200, in gmane.comp.lib.boost.user,Markus
> Schöpflin <markus.schoepflin_at_[hidden]> wrote:
> 
>> Marty Fried wrote:
>>
>> [snip compilation problem with filesystem]
>>
>> 1) Could you try if it works with the trunk version? There have been a few 
>> fixes in this area, but I don't know if those will help you.
>>
>> 2) Filesystem has passed the tests for 1.34.1 with cxx on Tru64 in strict 
>> ansi mode, which is usually good at finding this kind of errors. So could 
>> you please post the minimal test case you found, this allows me to check if 
>> cxx should have found the problem, and if yes, why I didn't find it.
>>
>> 3) If you have a fix and are confident that it works, open a ticket on the 
>> boost trac system, attaching a patch, preferably against the trunk version.. 
>> If you don't have a fix but are confident that it is an error, open a 
>> ticket anyway. ;-)
>>
>> 4) Which front-end does xlC use? EDG?
> 
> Thanks Markus,
> 
> 1.  I had looked over the trunk version, and compared it with the existing
> 1.34.1 version.  I didn't see anything that looked like it was remotely 
> related to this problem.  If you insist, I can try to pull down the files; I
> don't know offhand how to do this correctly, but I imagine I can figure out
> a way to do it.

No worry, I just remembered that we have regression test runs for xlC on 
the trunk. See 
http://beta.boost.org/development/tests/trunk/developer/summary.html for 
details on the state of xlC. Looks like xlC has its problems with boost code.

> 2.  My coworker came up with this minimal test case.  It has one level of
> indirection rather than 2 like filesystem, because that's all that's
> required to exhibit the problem.  Without the one level of indirection, MSVC
> and GCC both also display the error.  As I mentioned in my original post,
> this sample was fed into a web form on the Comeau site, which will check 
> the code for compliancy with the standard.  It's the best we have available
> for testing.  As I understand it, the mechanism is that the real function
> remove_all() (not the template function) forces instantiation of the
> template function remove_all(), which in turn forces the instantiation of
> the template function remove_all_aux(), which in turn forces the
> instantiation of basic_directory_iterator, before its definition later in
> the file.
> 
> I think the test case is small enough to post in this message, so here it
> is:
> /********  Test case  ********/
> 
> template <typename T> class foo;
> 
> template <typename T>
> inline void templatefunc()
> {
>    foo<int> f;
> }
> 
> inline void func()
> {
>    templatefunc<int>();
> }
>  
> template <typename T>
> class foo
> {
> };
> 
> /********  Results from Comeau compiler  *********/
> 
> Comeau C/C++ 4.3.9 (Mar 27 2007 17:24:47) for ONLINE_EVALUATION_BETA1
> Copyright 1988-2007 Comeau Computing.  All rights reserved.
> MODE:strict errors C++ C++0x_extensions
>  
> "ComeauTest.c", line 6: error: incomplete type is not allowed
>      foo<int> f;
>               ^
> 
> "ComeauTest.c", line 6: warning: variable "f" was declared but never
> referenced
>      foo<int> f;
>               ^
> 
> 1 error detected in the compilation of "ComeauTest.c".
> 
> /********  End test case  ********/

Hmm, cxx has this to say:

cxx: Error: foo.cxx, line 6: Cannot create variable "f" of incomplete type
           "foo<int>".
           detected during instantiation of
                     "void templatefunc<T>() [with T=int]" at line 11
    foo<int> f;
------------^

Now I'm left wondering why the tests on Tru64 don't show this error. Just 
to be sure, do you get the error while compiling the filesystem lib itself 
or while using the compiled filesystem lib?

If you get the error during compilation of the library, are you sure that 
above code is a valid reproducer for the original problem? (I'm not 
implying that it isn't, I just want to make sure it is.)

> 3.  Our fix would most likely be to compile the filesystem library with less
> strict compatibility checking.  I'm not envolved at all with the standards
> process, so I can't really know for sure how confident I should be that this
> is an error.  I've heard that Comeau C++ was used to find error in other
> compilers, like gcpp, so that is the main reason I think it's an error.

Well, I usually use Comeau to back up my claims when reporting an error, 
like you do. I'll cross post this to the developer list, maybe someone can 
confirm that this is indeed an error.

> 4.  We use xlC_r, the reentrant version of xlC (xlc++).  I don't really know
> what EDG is, but I'm pretty sure we don't use it.  FWIW, we currently have
> version 8, but will try to get version 9, which was recently released.  But
> I suspect that would only be more strict rather than less so.

EDG is a compiler front end, see 
http://www.edg.com/index.php?location=c_frontend for more details. But it 
seems xlC isn't using EDG.

Markus