bpo-36346: Make using the legacy Unicode C API optional (GH-21437)

Add compile time option USE_UNICODE_WCHAR_CACHE. Setting it to 0
makes the interpreter not using the wchar_t cache and the legacy Unicode C API.

2 files changed, 27 insertions, 6 deletions

diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index 8431c5b..5702ab2 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -166,11 +166,14 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
 {
     dl_funcptr p;
     char funcname[258], *import_python;
-    const wchar_t *wpathname;
 
     _Py_CheckPython3();
 
-    wpathname = _PyUnicode_AsUnicode(pathname);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpathname = _PyUnicode_AsUnicode(pathname);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpathname = PyUnicode_AsWideCharString(pathname, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpathname == NULL)
         return NULL;
 
@@ -192,6 +195,9 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
                               LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
                               LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
         Py_END_ALLOW_THREADS
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(wpathname);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
         /* restore old error mode settings */
         SetErrorMode(old_mode);
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 2c86828..50ef3c1 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -1008,15 +1008,21 @@ _Py_stat(PyObject *path, struct stat *statbuf)
 #ifdef MS_WINDOWS
     int err;
     struct _stat wstatbuf;
-    const wchar_t *wpath;
 
-    wpath = _PyUnicode_AsUnicode(path);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpath = _PyUnicode_AsUnicode(path);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpath = PyUnicode_AsWideCharString(path, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpath == NULL)
         return -2;
 
     err = _wstat(wpath, &wstatbuf);
     if (!err)
         statbuf->st_mode = wstatbuf.st_mode;
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     return err;
 #else
     int ret;
@@ -1433,7 +1439,6 @@ _Py_fopen_obj(PyObject *path, const char *mode)
     FILE *f;
     int async_err = 0;
 #ifdef MS_WINDOWS
-    const wchar_t *wpath;
     wchar_t wmode[10];
     int usize;
 
@@ -1448,7 +1453,11 @@ _Py_fopen_obj(PyObject *path, const char *mode)
                      Py_TYPE(path));
         return NULL;
     }
-    wpath = _PyUnicode_AsUnicode(path);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpath = _PyUnicode_AsUnicode(path);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpath = PyUnicode_AsWideCharString(path, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpath == NULL)
         return NULL;
 
@@ -1456,6 +1465,9 @@ _Py_fopen_obj(PyObject *path, const char *mode)
                                 wmode, Py_ARRAY_LENGTH(wmode));
     if (usize == 0) {
         PyErr_SetFromWindowsErr(0);
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return NULL;
     }
 
@@ -1465,6 +1477,9 @@ _Py_fopen_obj(PyObject *path, const char *mode)
         Py_END_ALLOW_THREADS
     } while (f == NULL
              && errno == EINTR && !(async_err = PyErr_CheckSignals()));
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #else
     PyObject *bytes;
     const char *path_bytes;