[arm-gnu] Fwd: Another Template related bug [compile time assertions with templates] - not sure whether this is a GCC bug

[Lars Kurth <larsk@xxxxxxxxxxx>]

Hi,

seems we may have come across a possible GCC bug. Not 100% sure though: 
the issue has to do with our definition of compile time assertions, 
which is defined as follows - using the well-formedness of a function 
definition to do the assertion.

    #define __ASSERT_COMPILE(x)  void __foo(int __check[x?1:-1])

Now it seems that in combination with templates, using the assert macro 
sometimes falls over, with the following error

  H:/epoc32/include/platform/elements/nm_signatures.h:505:
  error: default template arguments may not be used in function templates

I attached an e-mail snippet, which shows when the we get the error and 
when not

  #*define*  __Align8  <http://developer.symbian.org/xref/epl/s?refs=__Align8&project=/MCL>(s) ((((s)+__Size8  <http://developer.symbian.org/xref/oss/xref/MCL/sf/os/kernelhwsrv/kernel/eka/include/e32des8.h#__Size8>-1)/__Size8  <http://developer.symbian.org/xref/oss/xref/MCL/sf/os/kernelhwsrv/kernel/eka/include/e32des8.h#__Size8>)*__Size8  <http://developer.symbian.org/xref/oss/xref/MCL/sf/os/kernelhwsrv/kernel/eka/include/e32des8.h#__Size8>)

The solution we propose is to use the macro outside the inlined 
function, which appears to work.

Best Regards
Lars

-------- Original Message --------
Subject: 	Re: Another Template related bug...
From: 	Daniel Rubio <danielr@xxxxxxxxxxx>


Hi Remek,

I have spent some time on this at the weekend.

1- The the assert macro expands as a function within member function of 
the templated class, and that is interpreted as a templated function, 
but only in THAT particular class template (see below, I tried to 
reproduce the problem with simpler code unsuccessfully):

If you put the assert outside of the member function 
declaration/implementation it serves the same purpose, i.e. the class 
instantiation will fail at compile time if the condition is false, and 
GCCE can build the component.
Please let me know if you think this is ok and then I will submit it as 
a fix

Template <class TSIGNATURE, TInt PAYLOADATTRIBOFFSET, class 
TATTRIBUTECREATIONPOLICY, TInt PAYLOADBUFFERMAXLEN = 
TSignalBase::KMaxInlineMessageSize>
class TSignatureWithPolymorphicPayloadMetaType : public 
TSignatureWithPolymorphicPayloadMetaTypeBase
{
public:
*_ASSERT_COMPILE(**PAYLOADATTRIBOFFSET == 
__Align8(PAYLOADATTRIBOFFSET))**; //This compiles*

    inline static MMetaType* NewL(const TAny* aMem, const TAny* aData)
        {
        // For some reason this assertion does not compile under x86gcc 
which complains
        // that a default template argument has been specified for a 
templated member
        // function.  There is no such function so this is probably a 
parser bug.
        #if !defined(__GCCXML__) && !defined(__X86GCC__)
*//__ASSERT_COMPILE(**PAYLOADATTRIBOFFSET == 
__Align8(PAYLOADATTRIBOFFSET))**; //This DOES NOT compile*
*
*        #endif
        return ::new ((TUint8*)aMem) 
TSignatureWithPolymorphicPayloadMetaType(aData);
        }


2 - I tried to write "similar" code (clearer) to test but I could not 
manage to reproduce the error, so I think it may be a parser error since 
in the original code in which somehow it assumes that the macro is a 
template fucntion when it is expanded. The main difference between my 
code and the original code is that I am using a simple class not derived 
from a base class:

#define __ASSERT_COMPILE(x)  void __foo(int __check[x?1:-1])
template <class T, int PAYLOAD>
class list {
    public:
    typedef unsigned int myType;
    inline static myType setSize (unsigned int x, unsigned int y, T myVar)
    {
    __ASSERT_COMPILE(PAYLOAD);
    }

    };
Unsurprisingly, this code compiles without any errors (if PAYLOAD>0).

Let me know.

Daniel.






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