fix: report the right line and column for CRLF and mixed line endings

tests/test_parser.py

@@ -41,6 +41,29 @@ def test_parser_should_raise_an_error_for_empty_tables() -> None:
     assert e.value.col == 1
 
 
+@pytest.mark.parametrize("line_ending", ["\n", "\r\n"])
+def test_parser_reports_the_same_position_regardless_of_line_ending(
+    line_ending: str,
+) -> None:
+    content = line_ending.join(["a = 1", "b = 2", "c = @", "d = 4"]) + line_ending
+
+    with pytest.raises(UnexpectedCharError) as e:
+        Parser(content).parse()
+
+    assert e.value.line == 3
+    assert e.value.col == 4
+
+
+def test_parser_reports_the_right_position_for_mixed_line_endings() -> None:
+    content = "a = 1\r\nb = 2\nc = @\r\n"
+
+    with pytest.raises(UnexpectedCharError) as e:
+        Parser(content).parse()
+
+    assert e.value.line == 3
+    assert e.value.col == 4
+
+
 def test_parser_should_raise_an_error_if_equal_not_found() -> None:
     content = """[foo]
 a {c = 1, d = 2}

tomlkit/source.py

@@ -230,11 +230,16 @@ def parse_error(
         return exception(line, col, *args, **kwargs)
 
     def _to_linecol(self) -> tuple[int, int]:
+        # `keepends` keeps each line's own terminator inside its length: a "\r\n"
+        # break occupies two characters, and assuming a single one made the
+        # running offset fall one behind per CRLF line, so an error later in the
+        # document was reported on the wrong line and column.
+        lines = self.splitlines(keepends=True)
         cur = 0
-        for i, line in enumerate(self.splitlines()):
-            if cur + len(line) + 1 > self.idx:
+        for i, line in enumerate(lines):
+            if cur + len(line) > self.idx:
                 return (i + 1, self.idx - cur)
 
-            cur += len(line) + 1
+            cur += len(line)
 
-        return len(self.splitlines()), 0
+        return len(lines), 0