Gyp and libuv

One open source project that I've heard a bit about recently is libuv.  A cross-platform asynchronous IO library, it is something that I can plug into Kristjan Valur's stacklesslib module.  And all the work writing the Python bindings has already been done by Saúl Ibarra Corretgé in his pyuv project.

Anyway, I spent some time today getting it compiling for Windows and thought I would post a note about gyp, so that I could remember to avoid the same problems in future.  Gyp is a pretty handy build system. Just define the gist of what needs to be compiled in a mildly arcane mark-up, and it will churn out Makefiles, Visual Studio projects and solutions and a range of other things.  However, as with most programming related things, it is the little details that trip you up and cause you to waste your time.

Missing include files

If you are compiling with Visual Studio 2008, and it includes inttypes.h or stdint.h, errors will occur as these files will not be present.

...
libuv\include\uv.h(54): fatal error C1083: Cannot open include file: 'stdint.h': No such file or directory
...

Apparently the solution to this, after a lot of googling on what constitutes a wi-fi connection over here in New Zealand,  is to download something like the custom msinttypes versions of these files.   And then bung them somewhere Visual Studio will find it.. wherever that is.

Overriding gyp settings

If you are compiling a static library with Visual Studio using gyp, it will start with a range of default settings.  You will not be able to override these settings no matter where you put your own custom versions in your gyp configuration file.  The specific problem I had was that Python extensions are compiled with a RuntimeLibrary setting of MultiThreadedDLL and libuv is compiled with a different setting of MultiThreaded.  These are of course incompatible, and a variety of compilation errors are caused by it.

...
LIBCMT.lib(crt0dat.obj) : error LNK2005: __amsg_exit already defined in MSVCRT.lib(MSVCR90.dll)
...
LINK : warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; use /NODEFAULTLIB:library
LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; use /NODEFAULTLIB:library
LIBCMT.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
build\lib.win32-2.7\pyuv.pyd : fatal error LNK1120: 1 unresolved externals

In order to force this gyp setting to change from the default, it needs to be defined within a conditional expression.  The default setting is also a conditional expression, and .. well.. work it out.  Maybe it's in the documentation somewhere, but not in a clearly stated way that I could find.