INFO: folly dependencies' runtime requirements export

[jjerphan]

Context

The conda packages' model inherently was made to distribute C/C++ libraries as a set of headers and dynamic shared objects. A necessary condition for this model to work in practice is to have all the stack's projects' ABI to be respected as an ABI mismatch at runtime can cause a variety of fatal failures for programs (such as missing symbols reported by Python library, crashes, silent errors, etc.).

Major versions of project are expected to change the ABI. Although it is expected that the ABI does not change on patch (or even minor) version for project using semantic versioning 2.0.0, it might be the case in practice. Hence there are no general rules for the compatible version range: this is really is project-dependent. ABI laboratory might give clues about some projects' expected ABI stability.

conda packages solve this problem by exporting runtime requirements to specify the compatibility range for projects' version.

Situation

folly was not designed to be distributed as a shared library, yet it is distributed on conda-forge as such for Unix.

In the past, folly's or one of its dependencies' builds have had ABI mismatch.

Bellow are referenced all the compilers' and dependencies' runtime requirements exports used by folly as of today to check whether its builds are sane.

Compilers related	Runtime requirements export
libgcc-ng	Expected to be stable.
_libgcc_mutex	Expected to be stable.
llvm-openmp	Expected to be stable.
libstdcxx-ng	Expected to be stable.

Folly dependency	Runtime requirements export	ABI Laboratory observation
libjemalloc	max_pin=None	Change on major version
jemalloc	max_pin=None	Change on major version
libboost	max_pin="x.x"	Change on minor version
libboost-headers	max_pin="x.x"	Change on minor version
libzlib	max_pin="x.x"	Change on minor version; not up to date
zstd	max_pin="x.x"	Change on minor version
bzip2	Default, i.e. max_pin="x"	None
gflags	max_pin="x.x"	Change on minor version
lz4-c	max_pin="x.x"	Change on minor version
glog	max_pin="x.x"	Change on minor version; not up to date
fmt	max_pin="x"	Change on minor version
xz	Default, i.e. max_pin="x"	Stable
icu	Default, i.e. max_pin="x"	None
snappy	max_pin="x.x"	Change on minor version
libsodium	max_pin="x.x.x"	Change on patch version
double-conversion	max_pin="x.x"	Seems stable apart from a change on minor version
libevent	max_pin="x.x.x"	Change on patch version
openssl	max_pin="x"	Change on major version
libaio	max_pin="x.x"	Seems stable