c++/10332: Template classes are not instantiated correctly in presense of #pragma pack()

[Loren James Rittle]

In article <3E9A8732.7000600@akella.com>,
"Igor A. Goussarov" <igusarov@akella.com> writes:

>>>> What is the scope of #pragma pack ? 
Igor> Apparently, from the line it is encountered at till the end of
Igor> translation unit or till the next #pragma pack.
>> In that case holding it in a global variable looks appropriate, no ?

>     Up to a certain degree, yes. The concept of "packing" is applied to 
> structures, thus the packing size is a property of each structure. 
> Holding it in a global variable is justifiable only if there's 
> absolutely no chance that this variable could potentially be altered 
> before it is used to create an internal compiler representation of the 
> structure in question. I grant that C plain structures are 
> "instantiated" immediately at the point of their definition. C++ 
> templates are not. [...]

>     By now, I'm most interested in figuring out the point of view of the 
> gcc developers: do you tend to think that the current interference of 
> #pragma pack and templates is an undocumented feature or an incorrect 
> behaviour?

Agreed.  The proper fix is to either (a) document what is happening,
only available if no external spec says we are doing something wrong,
or (b) retain the global flag but capture it's value and bind it for
use when the C++ template is actually instantiated.

I'd favor (b) unless disallowed by the spec(s) that we claim to
implement for this pragma.  This is either an easy patch (if the
infrastructure allows it) or a nightmare (if it doesn't).  FYI, if
updating the documentation is not enough, this is outside my area to
productively fix.

Regards,
Loren