bpo-36142: Add preconfig.c (GH-12128)

* Add _PyArgv_Decode() function
* Move _Py_ClearFileSystemEncoding() and _Py_SetFileSystemEncoding()
  to preconfig.c.

Python/preconfig.c

@@ -0,0 +1,92 @@
+#include "Python.h"
+#include "pycore_coreconfig.h"
+
+
+#define DECODE_LOCALE_ERR(NAME, LEN) \
+    (((LEN) == -2) \
+     ? _Py_INIT_USER_ERR("cannot decode " NAME) \
+     : _Py_INIT_NO_MEMORY())
+
+
+/* --- File system encoding/errors -------------------------------- */
+
+/* The filesystem encoding is chosen by config_init_fs_encoding(),
+   see also initfsencoding(). */
+const char *Py_FileSystemDefaultEncoding = NULL;
+int Py_HasFileSystemDefaultEncoding = 0;
+const char *Py_FileSystemDefaultEncodeErrors = NULL;
+int _Py_HasFileSystemDefaultEncodeErrors = 0;
+
+void
+_Py_ClearFileSystemEncoding(void)
+{
+    if (!Py_HasFileSystemDefaultEncoding && Py_FileSystemDefaultEncoding) {
+        PyMem_RawFree((char*)Py_FileSystemDefaultEncoding);
+        Py_FileSystemDefaultEncoding = NULL;
+    }
+    if (!_Py_HasFileSystemDefaultEncodeErrors && Py_FileSystemDefaultEncodeErrors) {
+        PyMem_RawFree((char*)Py_FileSystemDefaultEncodeErrors);
+        Py_FileSystemDefaultEncodeErrors = NULL;
+    }
+}
+
+
+/* Set Py_FileSystemDefaultEncoding and Py_FileSystemDefaultEncodeErrors
+   global configuration variables. */
+int
+_Py_SetFileSystemEncoding(const char *encoding, const char *errors)
+{
+    char *encoding2 = _PyMem_RawStrdup(encoding);
+    if (encoding2 == NULL) {
+        return -1;
+    }
+
+    char *errors2 = _PyMem_RawStrdup(errors);
+    if (errors2 == NULL) {
+        PyMem_RawFree(encoding2);
+        return -1;
+    }
+
+    _Py_ClearFileSystemEncoding();
+
+    Py_FileSystemDefaultEncoding = encoding2;
+    Py_HasFileSystemDefaultEncoding = 0;
+
+    Py_FileSystemDefaultEncodeErrors = errors2;
+    _Py_HasFileSystemDefaultEncodeErrors = 0;
+    return 0;
+}
+
+
+/* --- _PyArgv ---------------------------------------------------- */
+
+_PyInitError
+_PyArgv_Decode(const _PyArgv *args, wchar_t*** argv_p)
+{
+    wchar_t** argv;
+    if (args->use_bytes_argv) {
+        /* +1 for a the NULL terminator */
+        size_t size = sizeof(wchar_t*) * (args->argc + 1);
+        argv = (wchar_t **)PyMem_RawMalloc(size);
+        if (argv == NULL) {
+            return _Py_INIT_NO_MEMORY();
+        }
+
+        for (int i = 0; i < args->argc; i++) {
+            size_t len;
+            wchar_t *arg = Py_DecodeLocale(args->bytes_argv[i], &len);
+            if (arg == NULL) {
+                _Py_wstrlist_clear(i, argv);
+                return DECODE_LOCALE_ERR("command line arguments",
+                                         (Py_ssize_t)len);
+            }
+            argv[i] = arg;
+        }
+        argv[args->argc] = NULL;
+    }
+    else {
+        argv = args->wchar_argv;
+    }
+    *argv_p = argv;
+    return _Py_INIT_OK();
+}