[Boost-build] Is there any way to prevent Boost.Build from recursively scanning header files for #include directives?

Subject: [Boost-build] Is there any way to prevent Boost.Build from recursively scanning header files for #include directives?
From: Lin Luo (chris.luolin_at_[hidden])
Date: 2009-04-27 04:06:17

Hi there,

We would like to know that is there a way to limit the header files that Boost.Build recursively scans for #include directives to a particular directory or set of directories? I.e. I'd like it to recursively scan the header files within my project only. I know that the external dependencies are not going to change (and being Boost and Qt they're pretty big). I end up with around 50,000 targets in the dependency tree which takes a while to process (resulting in a 1-2 minute build time even if no files have actually changed).

The only solution I've found so far is to take advantage of the INCLUDE environment variable (I'm using MSVC) - this means Boost.Build need not be informed of the include paths (I'm using the feature) and hence will not scan them. This seems a bit of a hack.

I feel like I must be missing something obvious because I haven't been able to find other people experiencing similar problems, even though I ran into this almost immediately. The closest I've come is here.

Judging from the debug output (bjam -d 3) it also scans most of the header files more than once... I don't know if this means that they are added as dependencies more than once, but certainly the cost of loading a file and scanning the entire contents must add up?

If I could tell it not to bother scanning a particular directory or set of directories in which I can guarantee the header files are not going to change, that would be perfect.

Thanks,

lluo / wbaker