Raise DeprecationWarning on raise_ioerror

Tests/test_imagefile.py

@@ -93,6 +93,11 @@ class TestImageFile:
 
         assert_image_equal(im1, im2)
 
+    def test_raise_ioerror(self):
+        with pytest.raises(IOError):
+            with pytest.raises(DeprecationWarning):
+                ImageFile.raise_ioerror(1)
+
     def test_raise_oserror(self):
         with pytest.raises(OSError):
             ImageFile.raise_oserror(1)

src/PIL/ImageFile.py

@@ -30,6 +30,7 @@
 import io
 import struct
 import sys
+import warnings
 
 from . import Image
 from ._util import isPath
@@ -64,6 +65,15 @@ def raise_oserror(error):
     raise OSError(message + " when reading image file")
 
 
+def raise_ioerror(error):
+    warnings.warn(
+        "raise_ioerror is deprecated and will be removed in a future release. "
+        "Use raise_oserror instead.",
+        DeprecationWarning,
+    )
+    return raise_oserror(error)
+
+
 def _tilesort(t):
     # sort on offset
     return t[2]