[cfe-dev] How do I try out C++ modules with clang?

[Stephen Kelly]

Sean Silva wrote:

> My experience has been that the easiest thing is to start out by just
> doing a "unity module" like
> 
> module foo {
> header "bar"
> header "baz"
> ...
> }
> 
> Just list every file in the directory (possibly recursively). Then just
> exclude any headers that are causing problems. That should get you up and
> running pretty fast.

I did this for Qt5Core and came up with  

 http://www.steveire.com/Qt5Core.modulemap

What is the next step? 

I'd like to understand more about the modulemap language and what should be 
specified there. What is the 'export *' stuff for? Qt headers define some 
macros such as Q_DECL_CONSTEXPR. Do they need to be explicitly 
named/exported in the modulemap file? The macro seems to work fine without 
such an export.

The headers that I exclude from the include/QtCore folder are:

 qatomic_armv5.h
 qatomic_armv6.h
 qatomic_armv7.h
 qatomic_bootstrap.h
 qatomic_cxx11.h
 qatomic_gcc.h
 qatomic_ia64.h
 qatomic_mips.h
 qatomic_msvc.h
 qatomic_unix.h
 qatomic_x86.h
 qconfig-dist.h
 qconfig.h
 qconfig-large.h
 qconfig-medium.h
 qconfig-minimal.h
 qconfig-nacl.h
 qconfig-small.h
 qobjectdefs_impl.h
 qobject_impl.h
 qsharedpointer_impl.h
 qt_windows.h

I *could* include qatomic_x86.h to the modulemap, but that header is not 
designed for users to include. Users include qatomic.h instead, which 
includes the appropriate _foo header.

The _impl headers are also not designed to be included directly, so not 
including those in the modulemap also makes sense to me. I suppose the 
appropriate version gets compiled into the module binary file included via 
the public header.

I guess on windows, qt_windows.h would need to be included in the modulemap 
(assuming windows.h was in another module, probably). So, we would have to 
generate the modulemap at the time of building/packaging Qt.

Thanks,

Steve.