Hi,

I noticed Python bindings is unable to load with Python 3.8.x on Windows, while 
trying
to run check-swig-py.

[[[
C:\usr\src\subversion\trunk-py3> python.exe -c "from svn import core; 
print(core.SVN_VERSION)"
Traceback (most recent call last):
  File "C:\usr\src\subversion\trunk-py3\Release\python\libsvn\core.py", line 
14, in swig_import_helper
    return importlib.import_module(mname)
  File "C:\usr\apps\python38\lib\importlib\__init__.py", line 127, in 
import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 657, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 556, in module_from_spec
  File "<frozen importlib._bootstrap_external>", line 1101, in create_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
ImportError: DLL load failed while importing _core: The specified module could 
not be found.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\usr\src\subversion\trunk-py3\Release\python\svn\core.py", line 26, in 
<module>
    from libsvn.core import *
  File "C:\usr\src\subversion\trunk-py3\Release\python\libsvn\core.py", line 17, in 
<module>
    _core = swig_import_helper()
  File "C:\usr\src\subversion\trunk-py3\Release\python\libsvn\core.py", line 
16, in swig_import_helper
    return importlib.import_module('_core')
  File "C:\usr\apps\python38\lib\importlib\__init__.py", line 127, in 
import_module
    return _bootstrap._gcd_import(name[level:], package, level)
ModuleNotFoundError: No module named '_core'
]]]

Investigating the issue, I found related changes in What's New In Python 3.8 
[1].

According to the document, DLL dependencies for *.pyd file doesn't search the 
directories
in PATH environment since Python 3.8 on Windows. We should call 
os.add_dll_directory() to
add search paths to resolve the dependencies.

I created patch to resolve the issue using moduleimport option of %module 
directive.
After attached patch, *.pyd file is successfully loaded and tests for Python 
bindings pass.

[[[
* subversion/bindings/swig/include/svn_global.swg
  (SVN_PYTHON_MODULEIMPORT): Add custom code to add search paths to resolve DLL
  dependencies when importing libsvn/*.pyd file.

* subversion/bindings/swig/core.i
* subversion/bindings/swig/svn_client.i
* subversion/bindings/swig/svn_delta.i
* subversion/bindings/swig/svn_diff.i
* subversion/bindings/swig/svn_fs.i
* subversion/bindings/swig/svn_ra.i
* subversion/bindings/swig/svn_repos.i
* subversion/bindings/swig/svn_wc.i
  Add moduleimport option with SVN_PYTHON_MODULEIMPORT to %module directive for
  Python.
]]]


[1] https://docs.python.org/3/whatsnew/3.8.html#bpo-36085-whatsnew

--
Jun Omae <jun6...@gmail.com> (大前 潤)
* subversion/bindings/swig/include/svn_global.swg
  (SVN_PYTHON_MODULEIMPORT): Add custom code to add search paths to resolve DLL
  dependencies when importing libsvn/*.pyd file.

* subversion/bindings/swig/core.i
* subversion/bindings/swig/svn_client.i
* subversion/bindings/swig/svn_delta.i
* subversion/bindings/swig/svn_diff.i
* subversion/bindings/swig/svn_fs.i
* subversion/bindings/swig/svn_ra.i
* subversion/bindings/swig/svn_repos.i
* subversion/bindings/swig/svn_wc.i
  Add moduleimport option with SVN_PYTHON_MODULEIMPORT to %module directive for
  Python.

Index: subversion/bindings/swig/core.i
===================================================================
--- subversion/bindings/swig/core.i     (revision 1877480)
+++ subversion/bindings/swig/core.i     (working copy)
@@ -23,8 +23,10 @@
  *   of the more specific module files.
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") core
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) core
 #elif defined(SWIGPERL)
 %module "SVN::_Core"
 #elif defined(SWIGRUBY)
@@ -31,8 +33,6 @@
 %module "svn::ext::core"
 #endif
 
-%include svn_global.swg
-
 %{
 #include <apr.h>
 #include <apr_general.h>
Index: subversion/bindings/swig/include/svn_global.swg
===================================================================
--- subversion/bindings/swig/include/svn_global.swg     (revision 1877480)
+++ subversion/bindings/swig/include/svn_global.swg     (working copy)
@@ -242,3 +242,40 @@
 /* Now, include the main Subversion typemap library. */
 %include svn_types.swg
 %include proxy.swg
+
+
+#ifdef SWIGPYTHON
+/* Since Python 3.8+ on Windows, DLL dependencies when loading *.pyd file
+ * searches only the system paths, the directory containing the *.pyd file and
+ * the directories added with os.add_dll_directory().
+ * See also https://bugs.python.org/issue36085.
+ */
+%define SVN_PYTHON_MODULEIMPORT
+"
+def _dll_paths():
+    import os
+    if hasattr(os, 'add_dll_directory'):  # Python 3.8+ on Windows
+        cookies = []
+        for path in os.environ.get('PATH', '').split(';'):
+            if path and os.path.isabs(path):
+                try:
+                    cookie = os.add_dll_directory(path)
+                except:
+                    continue
+                else:
+                    cookies.append(cookie)
+        return cookies
+    else:
+        return ()
+
+_dll_paths = _dll_paths()
+try:
+    from . import $module
+finally:
+    _dll_path = None
+    for _dll_path in _dll_paths:
+        _dll_path.close()
+    del _dll_paths, _dll_path
+"
+%enddef
+#endif
Index: subversion/bindings/swig/svn_client.i
===================================================================
--- subversion/bindings/swig/svn_client.i       (revision 1877480)
+++ subversion/bindings/swig/svn_client.i       (working copy)
@@ -21,8 +21,10 @@
  * svn_client.i: SWIG interface file for svn_client.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") client
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) client
 #elif defined(SWIGPERL)
 %module "SVN::_Client"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::client"
 #endif
 
-%include svn_global.swg
 %import core.i
 %import svn_delta.i
 %import svn_wc.i
Index: subversion/bindings/swig/svn_delta.i
===================================================================
--- subversion/bindings/swig/svn_delta.i        (revision 1877480)
+++ subversion/bindings/swig/svn_delta.i        (working copy)
@@ -21,8 +21,10 @@
  * svn_delta.i: SWIG interface file for svn_delta.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") delta
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) delta
 #elif defined(SWIGPERL)
 %module "SVN::_Delta"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::delta"
 #endif
 
-%include svn_global.swg
 %import core.i
 
 #ifdef SWIGRUBY
Index: subversion/bindings/swig/svn_diff.i
===================================================================
--- subversion/bindings/swig/svn_diff.i (revision 1877480)
+++ subversion/bindings/swig/svn_diff.i (working copy)
@@ -21,8 +21,10 @@
  * svn_diff.i: SWIG interface file for svn_diff.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") diff
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) diff
 #elif defined(SWIGPERL)
 %module "SVN::_Diff"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::diff"
 #endif
 
-%include svn_global.swg
 %import core.i
 
 /* -----------------------------------------------------------------------
Index: subversion/bindings/swig/svn_fs.i
===================================================================
--- subversion/bindings/swig/svn_fs.i   (revision 1877480)
+++ subversion/bindings/swig/svn_fs.i   (working copy)
@@ -21,8 +21,10 @@
  * svn_fs.i: SWIG interface file for svn_fs.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") fs
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) fs
 #elif defined(SWIGPERL)
 %module "SVN::_Fs"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::fs"
 #endif
 
-%include svn_global.swg
 %import core.i
 %import svn_delta.i
 
Index: subversion/bindings/swig/svn_ra.i
===================================================================
--- subversion/bindings/swig/svn_ra.i   (revision 1877480)
+++ subversion/bindings/swig/svn_ra.i   (working copy)
@@ -21,8 +21,10 @@
  * svn_ra.i: SWIG interface file for svn_ra.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") ra
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) ra
 #elif defined(SWIGPERL)
 %module "SVN::_Ra"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::ra"
 #endif
 
-%include svn_global.swg
 %import core.i
 %import svn_delta.i
 
Index: subversion/bindings/swig/svn_repos.i
===================================================================
--- subversion/bindings/swig/svn_repos.i        (revision 1877480)
+++ subversion/bindings/swig/svn_repos.i        (working copy)
@@ -21,8 +21,10 @@
  * svn_repos.i: SWIG interface file for svn_repos.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") repos
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) repos
 #elif defined(SWIGPERL)
 %module "SVN::_Repos"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::repos"
 #endif
 
-%include svn_global.swg
 %import core.i
 %import svn_delta.i
 %import svn_fs.i
Index: subversion/bindings/swig/svn_wc.i
===================================================================
--- subversion/bindings/swig/svn_wc.i   (revision 1877480)
+++ subversion/bindings/swig/svn_wc.i   (working copy)
@@ -21,8 +21,10 @@
  * svn_wc.i: SWIG interface file for svn_wc.h
  */
 
+%include svn_global.swg
+
 #if defined(SWIGPYTHON)
-%module(package="libsvn") wc
+%module(package="libsvn", moduleimport=SVN_PYTHON_MODULEIMPORT) wc
 #elif defined(SWIGPERL)
 %module "SVN::_Wc"
 #elif defined(SWIGRUBY)
@@ -29,7 +31,6 @@
 %module "svn::ext::wc"
 #endif
 
-%include svn_global.swg
 %import core.i
 %import svn_delta.i
 %import svn_ra.i

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