Let’s take a deep breath. You probably remember I’m running a tinderbox which is testing some common base system packages before they are unmasked (and thus unleashed on users); in particular I use it for testing new releases of GCC (4.7) and GLIBC (2.16).
It didn’t take me much after starting GLIBC 2.16 testing to find out that the previously-latest version of Boost (1.49) was not going to work with it. The problem is that there is a new definition that both of them tried to provide, TIME_UTC (probably relates to C++11/C11). Now unfortunately since it’s an API breakage to replace that definition, it means that it can’t be applied to the older versions, and it means that packages need to be fixed. Furthermore, the new 1.50 version has also broken the temporary compatibility introduced in 1.48 for their filesystem module’s API. This boils down to a world of pain for maintainers of packages using Boost (which includes yours truly, luckily none is directly maintained by me, just proxy).
So I had to add one extra package to the list, and ran the reverse dependencies — the positive side is that it didn’t take long to fill the bug although there are still a few issues with older boost versions not being supported yet. This brought up a few issues though…
First problem is the way Boost build itself, and its tests, is obnoxious: it’s totally serial, no parallelisation at all! The result is that to run the whole testsuite it takes over eight hours on Excelsior! The big issue is that for the testing, it takes some 10-20 times longer to build the test than run it (lovely language, C++), so a parallel build of the tests, even if the tests were executed in series, would mean a huge impact, and would also likely mean that the tests would become meaningful. As they sit, the (so-called) maintainer of the package has admitted to not run them when he revbumps, but only on full new versions.
The second problem is how Boost versions are discovered. The main issue is that Boost, instead of using proper sonames to keep binary compatibility, embeds its major/minor version pair in the library name — although most distributions symlinks the preferred version to the unversioned name (in Gentoo this is handled through the eselect boost tool). This is not extremely far from what most distributions do with Berkeley DB — but it causes problem when you have to find which one you should link to, especially when you consider that sometimes the unversioned name is not there at all.
So both CMake and Autotools (actually Autoconf Archive) provide macros to try a few different libraries. The former does it almost properly, starting from the highest version and then going in descending order — but uses a pre-defined list of versions to try! Which mean that most packages with CMake will try 1.49 first, as they don’t know that 1.50 is out yet! If no known version is found, then it will fallback to the unversioned library, which makes it work quite differently whether you have only one or more than one version installed!
For what concerns the macros from Autoconf Archive, they are quite nasty; from one side they really aren’t portable at all, as they use GNU sed syntax, they use uname (which makes them totally useless during cross-compilation), but most worrisome of all, is that they use ls to find which boost libraries are available and then take the first one that is usable. This means that if you have 1.50, 1.49 and 1.44 installed, it’ll use the oldest! Similarly to CMake, it uses the unversioned library last. In this case, though, I was able to improve the macros by reversing the check order, which makes them work correctly for most distributions out there.
What is even funnier about the AX macros (that were created for libtorrent, and are used by Gource, which I proxy-maintain for Enrico), is that due to the way they are implemented, it is feasible that they end up using the old libraries and the new headers (it was the case for me here with 1.49⁄1.50, as it didn’t fail to compile, just to link). As long as the interface used have different names and the linker will error out, all is fine. But if you have interfaces that are source-compatible, linker-compatible, but with different vtables, you have a crash waiting to happen.
Oh well…
