Rewrite runtine path lookup to libzim in wrapper for macOS

* Using fix for the `build_ext --rpath` on macOS that has an incorrect behavior
See https://bugs.python.org/issue36353
* Using a new `$RPATH` var in release workflow to
set `$ORIGIN` on Linux or `@loader_path/` on macOS
* Manually set (using install_name_tool) the wrapper's rpath for libzim
as the linker doesn't set it properly anyway.

Users of the PyPi releases (wheels created in the release workflow) will thus always
make use of the bundled libzim.

Author: renaud gaudin

.github/workflows/release.yml

@@ -38,6 +38,7 @@ jobs:
           echo ::set-env name=LIBZIM_RELEASE::libzim_macos-x86_64-$LIBZIM_VERSION
           echo ::set-env name=LIBZIM_LIBRARY_PATH::lib/libzim.${LIBZIM_VERSION:0:1}.dylib
           echo ::set-env name=PLAFTORM_NAME::macosx_10.9_x86_64
+          echo ::set-env name=RPATH::@loader_path/
 
       - name: set linux environ
         if: matrix.os == 'ubuntu-latest'
@@ -46,6 +47,7 @@ jobs:
           echo ::set-env name=LIBZIM_RELEASE::libzim_linux-x86_64-$LIBZIM_VERSION
           echo ::set-env name=LIBZIM_LIBRARY_PATH::lib/x86_64-linux-gnu/libzim.so.$LIBZIM_VERSION
           echo ::set-env name=PLAFTORM_NAME::manylinux1_x86_64
+          echo ::set-env name=RPATH::\$ORIGIN
 
       - name: Cache libzim dylib & headers
         uses: actions/cache@master
@@ -78,15 +80,17 @@ jobs:
       - name: Build cython, sdist, and bdist_wheels
         run: |
           pip install --upgrade "cython>=0.29.20,<3.0" setuptools pip wheel
-          python3 setup.py build_ext --rpath='$ORIGIN'
+          python3 setup.py build_ext --rpath $RPATH
           if [[  "${{ matrix.python-version }}" == "3.6" ]]
           then
             python3 setup.py sdist
           fi
 
       - name: add macOS libzim binary to source for wheel
         if: matrix.os == 'macos-latest'
-        run: cp -p lib/libzim.${LIBZIM_VERSION:0:1}.dylib libzim
+        run: |
+          install_name_tool -change libzim.6.dylib @loader_path/libzim.6.dylib $(find build -name "wrapper*.so")
+          cp -p lib/libzim.${LIBZIM_VERSION:0:1}.dylib libzim
 
       - name: add Linux libzim binary to source for wheel
         if: matrix.os == 'ubuntu-latest'

setup.py

@@ -34,6 +34,7 @@
 
 from setuptools import setup, Extension
 from Cython.Build import cythonize
+from Cython.Distutils.build_ext import new_build_ext as build_ext
 
 GITHUB_URL = "https://github.com/openzim/python-libzim"
 BASE_DIR = Path(__file__).parent
@@ -42,6 +43,21 @@
 LIBZIM_DYLIB = 'libzim.{ext}'.format(ext='dylib' if platform.system() == 'Darwin' else 'so')
 
 
+class fixed_build_ext(build_ext):
+    """Workaround for rpath bug in distutils for OSX."""
+
+    def finalize_options(self):
+        super().finalize_options()
+        # Special treatment of rpath in case of OSX, to work around python
+        # distutils bug 36353. This constructs proper rpath arguments for clang.
+        # See https://bugs.python.org/issue36353
+        if platform.system() == 'Darwin':
+            for path in self.rpath:
+                for ext in self.extensions:
+                    ext.extra_link_args.append("-Wl,-rpath," + path)
+            self.rpath[:] = []
+
+
 # Check for the CPP Libzim library headers in expected directory
 if not (BASE_DIR / LIBZIM_INCLUDE_DIR / 'zim/zim.h').exists():
     print(
@@ -96,6 +112,7 @@ def get_long_description():
 
     # Content
     packages=["libzim"],
+    cmdclass={'build_ext': fixed_build_ext},
     ext_modules=cythonize([wrapper_extension],
         compiler_directives={"language_level": "3"}
     ),