A simple HelloWorld program with zero includes except iostream triggers
a build of ca. 2000 source files. The reason is that ClickHouse's
top-level CMakeLists.txt overrides "add_executable()" to link all
binaries against "clickhouse_new_delete". This links against
"clickhouse_common_io", which in turn has lots of 3rd party library
dependencies ... Without linking "clickhouse_new_delete", the number of
compiled files for "HelloWorld" goes down to ca. 70.
As an example, the self-extracting-executable needs none of its current
dependencies but other programs may also benefit.
In order to restore access to the original "add_executable()", the
overriding version is now prefixed. There is precedence for a
"clickhouse_" prefix (as opposed to "ch_"), for example
"clickhouse_split_debug_symbols". In general prefixing makes sense also
because overriding CMake commands relies on undocumented behavior and is
considered not-so-great practice (*).
(*) https://crascit.com/2018/09/14/do-not-redefine-cmake-commands/
GCC support these days is experimental. GCCs main use is to keep the
code portable but I don't think it's used for performance tests. Hence
removing a performance workaround added in the GCC 7 days (we are now
using 11, soon: 12).
Globbing generally misses to pick up files which were added/deleted
after CMake's configure. This is a nuissance but can be alleviated using
CONFIGURE_DEPENDS (available since CMake 3.12) which adds a check for
new/deleted files before each compile and - if necessary - restarts the
configuration. On my system, the check takes < 0.1 sec.
(Side note: CONFIGURE_DEPENDS is not guaranteed to work accross all
generators, but at least it works for Ninja which everyone @CH seems to
use.)
