ARROW-5050: [C++] Specify dependencies of grpc_ep

[mrkn]

I encounter the following build error when I built the tarball of 0.13.0 RC.

[38/597] Performing configure step for 'grpc_ep'
FAILED: grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure
cd /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-build && /opt/brew/Cellar/cmake/3.13.3/bin/cmake -P /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure-RELEASE.cmake && /opt/brew/Cellar/c
make/3.13.3/bin/cmake -E touch /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure
CMake Error at /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure-RELEASE.cmake:16 (message):
Command failed: 1
'/opt/brew/Cellar/cmake/3.13.3/bin/cmake' '-DCMAKE_BUILD_TYPE=RELEASE' '-DCMAKE_PREFIX_PATH=';/opt/brew;/Users/mrkn/src/github.com/apache/arrow/cpp/build/gflags_ep-prefix/src/gflags_ep;/Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/thirdparty/cares_ep-install;'' '-DgRPC
_CARES_PROVIDER=package' '-DgRPC_GFLAGS_PROVIDER=package' '-DgRPC_PROTOBUF_PROVIDER=package' '-DgRPC_SSL_PROVIDER=package' '-DgRPC_ZLIB_PROVIDER=package' '-DCMAKE_CXX_FLAGS= -Qunused-arguments -fcolor-diagnostics -O3 -DNDEBUG -O3 -DNDEBUG -fPIC' '-DCMAKE_C_FLAGS= -Qunused-arguments -O3 -DNDEBUG -O3 -DNDEBUG -fPIC' '-DCMAKE_INSTALL_PREFIX=/Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/thirdparty/grpc_ep-install' '-DCMAKE_INSTALL_LIBDIR=lib' '-DProtobuf_PROTOC_LIBRARY=/opt/brew/lib/libprotoc.dylib' '-DBUILD_SHARED_LIBS=OFF' '-GNinja' '/Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep' See also /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure-*.log

grpc_ep's build log is given below:

$ cat /Users/mrkn/Downloads/apache-arrow-0.13.0/cpp/build/grpc_ep-prefix/src/grpc_ep-stamp/grpc_ep-configure-*.log
CMake Error at cmake/cares.cmake:38 (find_package):
Could not find a package configuration file provided by "c-ares" with any
of the following names:
c-aresConfig.cmake
c-ares-config.cmake
Add the installation prefix of "c-ares" to CMAKE_PREFIX_PATH or set
"c-ares_DIR" to a directory containing one of the above files. If "c-ares"
provides a separate development package or SDK, be sure it has been
installed.
Call Stack (most recent call first):
CMakeLists.txt:139 (include)
(snip)

This build log says that grpc_ep couldn't find cares_ep.
In this case, grpc_ep was built before cares_ep.

This pull-request could fix this dependency error on my environment.

[mrkn]

IMHO this isn't necessary for 0.13.0.

[pitrou]

+1. For those who like me are surprised that add_dependencies doesn't suffice, here is what the CMake doc says:

Because the external project uses additional custom targets internally for each step, the DEPENDS option is the most convenient way to ensure all of those steps depend on the other targets. Simply doing add_dependencies(<name> <targets>) will not make any of the steps dependent on <targets>.

[wesm]

+1. Flight / gRPC is still pretty alpha in 0.13 so I don't think this needs to be fixed in RC4 (Flight isn't in the verification script yet either)

https://issues.apache.org/jira/browse/ARROW-5054