MacOS: Cannot pip install from source due to hard-coded RPATH

[dpad]

Describe the bug
The current settings for the RPATH (path where the linker tries to find linked libraries) seem to be hard-coded to the absolute build directory for MacOS builds. This affects pip-based installation for MacOS, in particular for cases where pip copies the source code into the temporary build directory. The following cases are affected (on MacOS only):

• ✅ pip install . -- works because the source code is not copied and points to the local build directory dist3
• ❌ pip install Basilisk*.tar.gz -- i.e. installing source distribution does not work, because pip will unzip the source into a temporary directory
• ❌ pip install git+https://github.com/AVSLab/basilisk.git -- as above

I'm not 100% sure what the correct fix is for setting the RPATH appropriately, but the following patch at least seems to work when I asked someone with a MacOS to test it.

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
   set(CMAKE_SKIP_BUILD_RPATH FALSE) # use, i.e. don't skip the full RPATH for the build tree
   set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE) # when building, don't use the install RPATH already (but later on when
                                            # installing)
-  set(CMAKE_INSTALL_RPATH "${CMAKE_BINARY_DIR}/Basilisk") # the RPATH to be used when installing
+  set(CMAKE_INSTALL_RPATH "${CMAKE_BINARY_DIR}/Basilisk"  # the RPATH to be used when installing
+      # Also add relative paths so we can install from wheel/sdist.
+      # TODO: Is there a proper way to set relative library paths without just
+      # guessing how many parent ".." directories to use?
+      "@loader_path"
+      "@loader_path/.."
+      "@loader_path/../.."
+  )
 
   # don't add the automatically determined parts of the RPATH which point to directories outside the build tree to the
   # install RPATH

To reproduce
Steps to reproduce the behavior:

1. On a MacOS, Try to install the source directly from git: pip install git+https://github.com/AVSLab/basilisk.git
2. Run something with Basilisk, see errors about missing libraries

Desktop (please complete the following information):

• OS: MacOS

[sassy-asjp]

Note that the patch for macOS mirrors what is already happening in Linux:

basilisk/src/CMakeLists.txt

Line 502 in bf17f69

set(CMAKE_INSTALL_RPATH "\$ORIGIN/../../")

Since I think that the files get put into the install directory by pip, instead of running some cmake generated installation command, it might be the best possible without really fiddling with how pip is installing the files.