Hello fellow Arrow Devs, we have merged the CMake refactor yesterday https://github.com/apache/arrow/pull/3688 and this means that the build system behaves a bit different. The main differences are:
* If you're in a conda environment, we automatically detect this using the environment variable $CONDA_PREFIX and expect that all dependencies (except jemalloc and ORC) are installed via conda. * Otherwise, we will look in the standard system paths for a dependency. If it isn't found, we use CMake's ExternalProject mechanism to build it. * The *_HOME variables are not longer use and are replaced by *_ROOT variables to use CMake's standard detection features. Be aware that dependencies are no longer written in all caps but their preferred casing as seen in https://github.com/apache/arrow/blob/0d302125abb4b514dba210f496c574a77ce4cd1d/cpp/cmake_modules/ThirdpartyToolchain.cmake#L41-L59 * You can manually select the way we detect dependencies via ARROW_DEPENDENCY_SOURCE https://github.com/apache/arrow/blob/0d302125abb4b514dba210f496c574a77ce4cd1d/cpp/CMakeLists.txt#L189-L207 The hope is that you as a developer should not normally need to change this and as packager for distributions, you can use `ARROW_DEPENDENCY_SOURCE=SYSTEM` to ensure that ExternalProject is not used but only packages from the package manager. If your system is in a non-default prefix, you can indicate this by setting ARROW_PACKAGE_PREFIX. Also, please clear your existing CMake directories and do a fresh built to avoid any problems. As well when you're using conda packages, please update them all using `conda update --all` as I have errors in the packaging directly on conda-forge instead of doing workarounds in our CMake code. A helpful information is here that conda-forge now provides a `compilers` package that provides the whole build toolchain. Uwe
