htod - convert C .h files to D import files

[Walter Bright]

Don Clugston wrote:
> A perfect H to D converter is probably impossible, because #defines are 
> so ambiguous.

Not just that, there are things like using "char" as "byte" in C code. 
There's no way to reliably distinguish the usages.

> It takes a human who knows how the header file is intended 
> to be used.

That's right. That's why the original declarations are included as 
comments to make it easy to go through the results line by line and 
check them.

> However, it ought to be possible to construct patch files to 
> apply to C headers prior to running them into htod. It also seems 
> feasible in the long term to persuade some open-source projects to make 
> their headers D-friendly.

That's why the __HTOD__ macro is predefined when running htod.

> I'm left wondering what this means for the Windows API project. I 
> certainly would have done things differently, if I'd known this was 
> coming. Where to now?

Windows would still need a lot of hand work because of its heavy 
dependence on the preprocessor. There are still nearly 100,000 lines of 
code to check.

What I hope is that the D outputting version of SWIG will no longer be 
necessary, that one can just run the C output of SWIG through htod. That 
way we can easily leverage all the work put into SWIG by others.