[FEA] Set -ffile_prefix_map when in a conda-build

[vyasr]

Is your feature request related to a problem? Please describe.
The issue that we would like to resolve is documented in rapidsai/build-planning#159.

Describe the solution you'd like
rapids-cmake's rapids_cmake_support_conda_env contains various bits of logic specialized to conda environments, and further, to building inside conda-build. Based on the discussions in rapidsai/build-planning#159, we should consider augmenting this feature to also remap the file prefix. This ensures that we do not embed non-relocatable paths into our binaries via the usage of the __FILE__ macro. We could inject this logic into the conda-build-specific sections of rapids_cmake_support_conda_env.

As long as we are fine with using the root of the C++ CMakeLists.txt as the new prefix, this should be straightforward. Things will get a bit hairier if we want to remap the base prefix to be something like the root of the repository (as demonstrated in rapidsai/rmm#1861) since that is a directory above the build, but it should still be possible

[vyasr]

Note that the original proposal in rapidsai/rmm#1861 is around fmacro-prefix-path. If we did ffile-prefix-path, we would also get -fdebug-prefix-map for free, which is important for ensuring sccache consistency (see prefix-dev/rattler-build#1458 and rapidsai/build-planning#47 (comment) for context) in rapids-cmake.

[jakirkham]

As context -fdebug-prefix-map is set by the Conda compilers when run in conda-build. Including the relevant bit below

"... -fdebug-prefix-map=${SRC_DIR}=/usr/local/src/conda/${PKG_NAME}-${PKG_VERSION} -fdebug-prefix-map=${PREFIX}=/usr/local/src/conda-prefix"

It is worth seeing whether we want to set -ffile-prefix-path to affect this or just remove it and use something like -fmacro-prefix-path for a more focused replacement

[jakirkham]

Am guessing we will want something like this in CMake

target_compile_options(${target} INTERFACE "$<$<COMPILE_LANGUAGE:C>:-ffile-prefix-path=$ENV{PREFIX}/=''>")
target_compile_options(${target} INTERFACE "$<$<COMPILE_LANGUAGE:CXX>:-ffile-prefix-path=$ENV{PREFIX}/=''>")
target_compile_options(${target} INTERFACE "$<$<COMPILE_LANGUAGE:CUDA>:-ffile-prefix-path=$ENV{PREFIX}/=''>")

Likely in this section

rapids-cmake/rapids-cmake/cmake/support_conda_env.cmake

Line 135 in a32bedb

if(in_conda_build)

Though Rob or Kyle would know more