reject overlong decimal integer instead of coercing to inf

tests/test_parser.py

@@ -2,9 +2,11 @@
 
 from tomlkit.exceptions import EmptyTableNameError
 from tomlkit.exceptions import InternalParserError
+from tomlkit.exceptions import InvalidNumberError
 from tomlkit.exceptions import InvalidUnicodeValueError
 from tomlkit.exceptions import ParseError
 from tomlkit.exceptions import UnexpectedCharError
+from tomlkit.items import Integer
 from tomlkit.items import StringType
 from tomlkit.parser import Parser
 
@@ -197,3 +199,16 @@ def test_parser_rejects_aot_header_missing_second_bracket(content: str) -> None:
     parser = Parser(content)
     with pytest.raises(ParseError):
         parser.parse()
+
+
+def test_parser_rejects_overlong_decimal_integer() -> None:
+    # A decimal integer with more digits than Python's int-from-string limit
+    # raises ValueError in int(); it must be reported as an invalid number, not
+    # silently fall through to float() and become inf.
+    parser = Parser("a = " + "9" * 4301)
+    with pytest.raises(InvalidNumberError):
+        parser.parse()
+
+    # the value just under the limit is still a normal integer
+    value = Parser("a = " + "9" * 4300).parse()["a"]
+    assert isinstance(value, Integer)

tomlkit/parser.py

@@ -786,11 +786,20 @@ def _parse_number(self, raw: str, trivia: Trivia) -> Item | None:
         try:
             return Integer(int(sign + clean, base), trivia, sign + raw)
         except ValueError:
+            pass
+
+        # Only fall back to float for an actual float literal (a fractional
+        # dot, a base-10 exponent, or inf/nan). A decimal integer whose digit
+        # count exceeds Python's int-from-string conversion limit also raises
+        # ValueError above; it must be rejected, not silently coerced to inf.
+        if base == 10 and ("." in clean or "e" in clean or clean in ("inf", "nan")):
             try:
                 return Float(float(sign + clean), trivia, sign + raw)
             except ValueError:
                 return None
 
+        return None
+
     def _parse_literal_string(self) -> String:
         with self._state:
             return self._parse_string(StringType.SLL)