+/* Given a Windows-style path, return the number of characters of the prefix
+ * that specify the path to the root directory of a drive, or return 0 if the
+ * drive is relative (or at least on the current drive, in the case of
+ * absolute-but-not-really-absolute paths like \Windows\System32) */
+static size_t
+win32_path_drive_spec_len(const wchar_t *path)
+{
+ size_t n = 0;
+
+ if (!wcsncmp(path, L"\\\\?\\", 4)) {
+ /* \\?\-prefixed path. Check for following drive letter and
+ * path separator. */
+ if (path[4] != L'\0' && path[5] == L':' &&
+ is_any_path_separator(path[6]))
+ n = 7;
+ } else {
+ /* Not a \\?\-prefixed path. Check for an initial drive letter
+ * and path separator. */
+ if (path[0] != L'\0' && path[1] == L':' &&
+ is_any_path_separator(path[2]))
+ n = 3;
+ }
+ /* Include any additional path separators.*/
+ if (n > 0)
+ while (is_any_path_separator(path[n]))
+ n++;
+ return n;
+}
+
+bool
+win32_path_is_root_of_drive(const wchar_t *path)
+{
+ size_t drive_spec_len;
+ wchar_t full_path[32768];
+ DWORD ret;
+
+ ret = GetFullPathName(path, ARRAY_LEN(full_path), full_path, NULL);
+ if (ret > 0 && ret < ARRAY_LEN(full_path))
+ path = full_path;
+
+ /* Explicit drive letter and path separator? */
+ drive_spec_len = win32_path_drive_spec_len(path);
+ if (drive_spec_len > 0 && path[drive_spec_len] == L'\0')
+ return true;
+
+ /* All path separators? */
+ for (const wchar_t *p = path; *p != L'\0'; p++)
+ if (!is_any_path_separator(*p))
+ return false;
+ return true;
+}
+
+