Invent DirtyZipInfo to create an unsanitized zipfile with backslashes.

tests/test_path.py

@@ -5,6 +5,7 @@
 import pickle
 import stat
 import sys
+import time
 import unittest
 from zipp.compat.overlay import zipfile
 
@@ -627,7 +628,7 @@ def test_backslash_not_separator(self):
         """
         data = io.BytesIO()
         zf = zipfile.ZipFile(data, "w")
-        zf.writestr("foo\\bar", b"content")
+        zf.writestr(DirtyZipInfo.for_name("foo\\bar", zf), b"content")
         zf.filename = ''
         root = zipfile.Path(zf)
         (first,) = root.iterdir()
@@ -640,3 +641,29 @@ def test_interface(self, alpharep):
 
         zf = zipfile.Path(alpharep)
         assert isinstance(zf, Traversable)
+
+
+class DirtyZipInfo(zipfile.ZipInfo):
+    """
+    Bypass name sanitization.
+    """
+
+    def __init__(self, filename, *args, **kwargs):
+        super().__init__(filename, *args, **kwargs)
+        self.filename = filename
+
+    @classmethod
+    def for_name(cls, name, archive):
+        """
+        Construct a ZipInfo the same way that ZipFile.writestr
+        does.
+        """
+        self = cls(filename=name, date_time=time.localtime(time.time())[:6])
+        self.compress_type = archive.compression
+        self.compress_level = archive.compresslevel
+        if self.filename.endswith('/'):
+            self.external_attr = 0o40775 << 16  # drwxrwxr-x
+            self.external_attr |= 0x10  # MS-DOS directory flag
+        else:
+            self.external_attr = 0o600 << 16  # ?rw-------
+        return self