Re: [Boost-build] Building generator (from source) that generates cpp

Subject: Re: [Boost-build] Building generator (from source) that generates cpp
From: Vladimir Prus (ghost_at_[hidden])
Date: 2009-06-30 08:47:19

On Monday 29 June 2009 Samuel Debionne wrote:

> Hello,
> I'm using BBV2 to build my own projects for quite a long time. Right now
> I'm facing the following issue : I want to generate CPP from an other type
> of file and I want this home made generator to be build from source when
> necessary. This is basically what Quickbook toolset does so I try to start
> from that.
> The strange thing is that, as long as I don't generate CPP but other file
> type (XML, what ever), it's fine. But when targeting CPP, I can't build
> the generator 'automatically'.
> 
> I include a small test case that shows my problem. To play with the test
> case, unzip next to your boost_1_39_0 directory.
> 
> If I try to build the generator directly (i.e. bjam tool/mygen with my
> test case) it's fine. If I try to build the target that uses the generator
> (i.e. bjam) I get the following message :
> 
> warn: Unable to construct tool/mygen
> error: no generators were found for type 'EXE'
> error: and the requested properties
> error: make sure you've configured the needed tools

Samuel,

what is happening is that you are building EXE target, which uses gcc.link
generator, which then recursively builds sources, invoking your custom
generator. This, in turn, tries to build another EXE target, again using
gcc.link generator. However, there's a safety net against infinite recursion,
which blocks second invocation of the same generator.

I have just checked in patch to make this logic somewhat more relaxed,
so if you update from SVN, your project should work.

If you wonder why this issue did not appear earlier, there are two
reasons:
1. quickbook generator is not building EXE, so this double-invocation
of generator does not happen.
2. The method quickbook uses is the most flexible, but also most
complex. The approach demonstrated by examples/built_tool is
considerably easier, and I suspect that's what most users do. Of
course, if your project works after SVN update, there's no reason
for you do change anything.

Hope this helps,
Volodya