Add support for the libclang package

A newer package provigind the python libclang bindings is available, called
"libclang". Unlike "clang", this package ships the libclang library, removing
the dependency from the system's one.

This commit adds support for it, using the libclang's builtin library if found
and if LIBCLANG_PATH and LLVM_DIR_PATH are not defined.

As libclang does not ship the clang standard library headers, some system
headers may not be found (like stddef.h), but the documentation generation
completes successfully anyways.

Author: corna

pybind11_mkdoc/mkdoc_lib.py

@@ -270,7 +270,7 @@ def read_args(args):
         sdk_dir = dev_path + 'Platforms/MacOSX.platform/Developer/SDKs'
         libclang = lib_dir + 'libclang.dylib'
 
-        if os.path.exists(libclang):
+        if cindex.Config.library_path is None and os.path.exists(libclang):
             cindex.Config.set_library_path(os.path.dirname(libclang))
 
         if os.path.exists(sdk_dir):
@@ -285,7 +285,7 @@ def read_args(args):
             else:
                 raise FileNotFoundError("Failed to find libclang.dll! "
                                         "Set the LIBCLANG_PATH environment variable to provide a path to it.")
-        else:
+        elif cindex.Config.library_path is None:
             library_file = ctypes.util.find_library('libclang.dll')
             if library_file is not None:
                 cindex.Config.set_library_file(library_file)
@@ -306,7 +306,7 @@ def folder_version(d):
         # Ability to override LLVM/libclang paths
         if 'LLVM_DIR_PATH' in os.environ:
             llvm_dir = os.environ['LLVM_DIR_PATH']
-        elif llvm_dir is None:
+        elif llvm_dir is None and cindex.Config.library_path is None:
             raise FileNotFoundError(
                 "Failed to find a LLVM installation providing the file "
                 "/usr/lib{32,64}/llvm-{VER}/lib/libclang.so.1. Make sure that "
@@ -319,12 +319,12 @@ def folder_version(d):
                 "variables.")
 
         if 'LIBCLANG_PATH' in os.environ:
-            libclang_dir = os.environ['LIBCLANG_PATH']
-        else:
-            libclang_dir = os.path.join(llvm_dir, 'lib', 'libclang.so.1')
+            cindex.Config.set_library_file(os.environ['LIBCLANG_PATH'])
+        elif cindex.Config.library_path is None:
+            cindex.Config.set_library_file(os.path.join(llvm_dir, 'lib',
+                                                        'libclang.so.1'))
 
-        cindex.Config.set_library_file(libclang_dir)
-        cpp_dirs = [ ]
+        cpp_dirs = []
 
         if '-stdlib=libc++' not in args:
             cpp_dirs.append(max(
@@ -335,11 +335,16 @@ def folder_version(d):
                 glob('/usr/include/%s-linux-gnu/c++/*' % platform.machine()
             ), default=None, key=folder_version))
         else:
+            if llvm_dir is None:
+                raise FileNotFoundError(
+                    "-stdlib=libc++ has been specified, but no LLVM "
+                    "installation have been found on the system.")
+
             cpp_dirs.append(os.path.join(llvm_dir, 'include', 'c++', 'v1'))
 
         if 'CLANG_INCLUDE_DIR' in os.environ:
             cpp_dirs.append(os.environ['CLANG_INCLUDE_DIR'])
-        else:
+        elif llvm_dir is not None:
             cpp_dirs.append(max(
                 glob(os.path.join(llvm_dir, 'lib', 'clang', '*', 'include')
             ), default=None, key=folder_version))