before this change, add_version_library() is a single function
which accomplishes two tasks:
1. build scylla-version target using
2. add an object library
but this has two problems:
1. we should run `SCYLLA-VERSION-GEN` at configure time, instead
of at build time. otherwise the targets which read from the
SCYLLA-{VERSION, RELEASE, PRODUCT}-FILE cannot access them,
unless they are able to read them in their build rules. but
they always use `file(STRINGS ..)` to read them, and thsee
`file()` command is executed at configure time. so, this
is a dead end.
2. we repeat the `file(STRING ..)` multiple places. this is
not ideal if we want to minimize the repeatings.
so, to address this problem, in this change:
1. use `execute_process()` instead of `add_custom_command()`
for generating these *-FILE files. so they are always ready
at build time. this partially reverts bb7d99ad37.
2. extract `generate_scylla_version()` out of `add_version_library()`.
so we can call the former much earlier than the latter.
this would allow us to reference the variables defined by
the `generate_scylla_version()` much earlier.
3. define cached strings in the extracted function, so that
they can consumed by other places.
4. reference the cached variables in `build_submodule.cmake`.
also, take this opportunity to fix the version string
used in build_submodule.cmake: we should have used
`scylla_version_tilde`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#14769
3ad844a4bb