Debugging a CMake dependency

[simgt]

I'm trying to link an example program against libtorch with Meson, using Torch's provided CMake modules. I'm on macOS. The original CMake-based example builds and runs fine:

# Configure with: cmake -DCMAKE_PREFIX_PATH=(python3 -c "import torch; print(torch.utils.cmake_prefix_path)") -B build
cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
project(libtorch-example)
find_package(Torch REQUIRED)
add_executable(example-app-cmake example-app.cpp)
message("${TORCH_LIBRARIES}")
target_link_libraries(example-app-cmake "${TORCH_LIBRARIES}")
set_property(TARGET example-app-cmake PROPERTY CXX_STANDARD 14)

I try to build the same code with Meson in the following way:

# Configure with: meson build --cmake-prefix-path=(python3 -c "import torch; print(torch.utils.cmake_prefix_path)")
project('libtorch-example', ['c', 'cpp'], default_options : ['cpp_std=c++14'])
torch = dependency('Torch', version : '>=1.10', method : 'cmake')
message(torch.get_variable(cmake : 'TORCH_LIBRARIES'))
executable('example-app-meson', 'example-app.cpp', dependencies : torch)

The program produced by meson fails to load libc10 that Torch provides, and I guess libtorch_cpu would follow.

The difference of linking in-between the two programs:

> otool -L build/example-app-meson
build/example-app-meson:
@rpath/libc10.dylib (compatibility version 0.0.0, current version 0.0.0)
@rpath/libtorch_cpu.dylib (compatibility version 0.0.0, current version 0.0.0)
/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1300.36.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1319.0.0)

> otool -L build/example-app-cmake
build/example-app-cmake:
/opt/homebrew/opt/libtorch/lib/libc10.dylib (compatibility version 0.0.0, current version 0.0.0)
/opt/homebrew/opt/libtorch/lib/libtorch.dylib (compatibility version 0.0.0, current version 0.0.0)
/opt/homebrew/opt/libtorch/lib/libtorch_cpu.dylib (compatibility version 0.0.0, current version 0.0.0)
/opt/homebrew/opt/protobuf/lib/libprotobuf.32.dylib (compatibility version 33.0.0, current version 33.4.0)
/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1300.36.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1319.0.0)

In meson, TORCH_LIBRARIES prints torch torch_library
whereas with cmake I get torch;torch_library;/opt/homebrew/lib/libc10.dylib;/opt/homebrew/lib/libkineto.a

The build seems to find c10 however:

> cat build/meson-private/cmake_Torch/CMakeCache.txt | grep c10
c10_LIBRARY:FILEPATH=/opt/homebrew/lib/libc10.dylib

Would you have any suggestions on how I could understand what's not working with the meson build? I'd like to recover some messages from the underlying TorchConfig.cmake but didn't find any obvious way to make the configuration verbose enough.

[simgt]

My issue was specifically linked to #3882, not sure what the motive is behind this feature.
Regarding debugging a dependency, it seems that there is barely anything outside of a few prints in meson-logs/ and meson-private/: #4563

[lterrac]

Ehy @simgt I am having the exact same issue! What solution did work for you specifically? :)