Reject non-ASCII case equivalents in country and currency codes

With ignore_case=True, country_code() and currency() compared
value.upper() against the ISO lists. str.upper() maps letters such as
dotless i (U+0131), long s (U+017F) and the fi ligature (U+FB01) onto
ASCII, so "ıt", "ıta", "fiN" and "uſd" were accepted as
IT, ITA, FIN and USD. Require ASCII input before case-insensitive
matching.

Author: Enesuygurs

src/validators/country.py

@@ -299,7 +299,8 @@ def country_code(value: str, /, *, iso_format: str = "auto", ignore_case: bool =
     if not value:
         return False
 
-    if not (1 < len(value) < 4):
+    # str.upper() would map e.g. dotless i and long s onto ASCII letters
+    if not (1 < len(value) < 4) or not value.isascii():
         return False
 
     if iso_format == "auto" and (iso_format := _get_code_type(value)) == "invalid":
@@ -349,7 +350,8 @@ def currency(value: str, /, *, skip_symbols: bool = True, ignore_case: bool = Fa
     if not skip_symbols and value in _currency_symbols:
         return True
 
-    if len(value) != 3:
+    # str.upper() would map e.g. dotless i and long s onto ASCII letters
+    if len(value) != 3 or not value.isascii():
         return False
 
     return value.upper() in _currency_iso4217 if ignore_case else value in _currency_iso4217

tests/test_country.py

@@ -55,6 +55,22 @@ def test_returns_failed_validation_on_invalid_country_code(value: str, iso_forma
     assert isinstance(country_code(value, iso_format=iso_format), ValidationError)
 
 
+@pytest.mark.parametrize(
+    ("value", "iso_format"),
+    [
+        ("\u0131t", "auto"),
+        ("\u017fe", "alpha2"),
+        ("\u0131ta", "auto"),
+        ("\ufb01N", "alpha3"),
+    ],
+)
+def test_returns_failed_validation_on_non_ascii_case_equivalent_country_code(
+    value: str, iso_format: str
+):
+    """Test returns failed validation when Unicode case mapping yields an ASCII code."""
+    assert isinstance(country_code(value, iso_format=iso_format, ignore_case=True), ValidationError)
+
+
 @pytest.mark.parametrize(
     ("value", "skip_symbols", "ignore_case"),
     [("$", False, False), ("⃀", False, False), ("৳", False, False), ("uSd", True, True)],
@@ -73,6 +89,8 @@ def test_returns_true_on_valid_currency(value: str, skip_symbols: bool, ignore_c
         ("⃀৳", False, False),
         ("uSd", True, False),
         ("Bucks", True, True),
+        ("u\u017fd", True, True),
+        ("\u0131ls", True, True),
     ],
 )
 def test_returns_failed_validation_invalid_currency(