SCons, VS.NET and VSIP

I’ve just upgraded to the latest version of SCons, and in doing so I noticed my little patch to get it working with VSIP needed reinstalling. This blog entry describes the problem and the little patch you need to make to fix it.

SCons is very low-maintainance to install — it automatically scours the registry for all the paths and information it needs to invoke the Visual Studio Compiler and all the other tools. However, when you install the VSIP package, the registry scanning code throws a benny.

VSIP installs an ‘Experimental’ (Exp) configuration of VS.NET — so you can test out all your VS.NET plugins without actually breaking your own development environment! By running the IDE with the ‘/RootSuffix Exp’ switch, the IDE will load up from this alternative configuration.

The issue is that this duplicates a bunch of registry keys, giving them a ‘Exp’ suffix. The registry keys in question are linked to the version number of VS.NET you’re using, HKLM/Software/Microsoft/Visual/Studio/keyname — and SCons uses this to enumerate and find all the versions of VS.NET you have installed. When it finds keys like ‘7.1Exp’ in there, it goes belly up trying to make a floating point number out of it!

My somewhat cheesey solution is to just ignore any keys where the number isn’t a valid float. A proper solution should probably take these into account — but realistically the normal settings should be ok to build with all the time, not the crazy Exp settings your plugin development requires!

To fix the issue, load up SConsToolmsvs.py and patch the get_visualstudio_versions function after the if not p[0] in '123456789' or p in L: continue

# Try converting 'p' to a floating point number.  Experimental
# versions of VS are named '7.0Exp' and '7.1Exp' etc.
# These don't fall into the numeric patterns the rest of the
# logic expects, so if we can't make a number from it, ignore it.
try:
    float(p)
except ValueError:
    continue