Push down the swig module to avoid an import cycle (llvm#129135)

Fix llvm#92603

This replaces llvm#113066. I finally came back to this issue and it seems
that this approach is still very promising.

As requested, I have added a short explanation as to why CPython module
should be moved into a submodule.

cc @JDevlieghere who reviewed on the previous PR earlier.

Author: dingxiangfei2009

lldb/bindings/python/CMakeLists.txt

@@ -59,8 +59,10 @@ endfunction()
 function(finish_swig_python swig_target lldb_python_bindings_dir lldb_python_target_dir)
   # Add a Post-Build Event to copy over Python files and create the symlink to
   # liblldb.so for the Python API(hardlink on Windows).
+  # Note that Swig-generated code is located one level deeper in the `native`
+  # module, in order to avoid cyclic importing.
   add_custom_target(${swig_target} ALL VERBATIM
-    COMMAND ${CMAKE_COMMAND} -E make_directory ${lldb_python_target_dir}
+    COMMAND ${CMAKE_COMMAND} -E make_directory ${lldb_python_target_dir}/native/
     DEPENDS ${lldb_python_bindings_dir}/lldb.py
     COMMENT "Python script sym-linking LLDB Python API")
 
@@ -74,6 +76,8 @@ function(finish_swig_python swig_target lldb_python_bindings_dir lldb_python_tar
       "${LLDB_SOURCE_DIR}/source/Interpreter/embedded_interpreter.py"
       "${lldb_python_target_dir}")
 
+  create_python_package(${swig_target} ${lldb_python_target_dir} "native" FILES)
+
   # Distribute the examples as python packages.
   create_python_package(
     ${swig_target}
@@ -141,7 +145,7 @@ function(finish_swig_python swig_target lldb_python_bindings_dir lldb_python_tar
   endif()
   set(LIBLLDB_SYMLINK_OUTPUT_FILE "_lldb${LLDB_PYTHON_EXT_SUFFIX}")
   create_relative_symlink(${swig_target} ${LIBLLDB_SYMLINK_DEST}
-                          ${lldb_python_target_dir} ${LIBLLDB_SYMLINK_OUTPUT_FILE})
+                          ${lldb_python_target_dir}/native/ ${LIBLLDB_SYMLINK_OUTPUT_FILE})
 
 
   if (NOT WIN32)

lldb/bindings/python/python.swig

@@ -50,7 +50,12 @@ Older swig versions will simply ignore this setting.
     import $module
 except ImportError:
     # Relative import should work if we are being loaded by Python.
-    from . import $module"
+    # The cpython module built by swig is pushed one level down into
+    # the native submodule, because at this point the interpreter
+    # is still constructing the lldb module itself.
+    # Simply importing anything using `from . import` constitutes
+    # a cyclic importing.
+    from .native import $module"
 %enddef
 
 // The name of the module to be created.