Fix edge case in insert_text_at_position when inserting in line beyond actual content

(insertion coordinates were not adjusted to true end coordinates)

src/solidlsp/ls_utils.py

@@ -263,9 +263,12 @@ class TextUtils:
             num_lines_in_text = text_stepper.line + 1
             max_line = num_lines_in_text - 1
             if line == max_line + 1 and col == 0:  # trying to insert at new line after full text
-                # insert at end, adding missing newline
+                # insert at end, adding missing newline and adjusting insertion position
+                # to the actual end coordinates of the text
                 change_index = len(text)
                 text_to_be_inserted = "\n" + text_to_be_inserted
+                line = text_stepper.line
+                col = text_stepper.col
             else:
                 raise
         new_text = text[:change_index] + text_to_be_inserted + text[change_index:]

test/solidlsp/test_text_utils.py

@@ -32,3 +32,19 @@ class TestTextUtils:
         assert TextUtils.get_index_from_line_col(self.TEXT, 0, 1) == 1
         assert TextUtils.get_index_from_line_col(self.TEXT, 1, 1) == 3 + 1 + 1
         assert TextUtils.get_index_from_line_col(self.TEXT, 2, 1) == 3 + 1 + 3 + 2 + 1
+
+    def test_insert_text_at_index(self):
+        insertion = "XXX"
+        new_text, l, c = TextUtils.insert_text_at_position(self.TEXT, 0, 1, insertion)
+        assert (l, c) == (0, 1 + len(insertion))
+        assert new_text.startswith("0XXX12")
+
+    def test_insert_text_in_next_line_beyond_content(self):
+        """
+        Test inserting text at a line index 1 beyond the actual number of lines.
+        This case is specifically handled as an edge case in the implementation.
+        """
+        insertion = "XXX"
+        new_text, l, c = TextUtils.insert_text_at_position(self.TEXT, 4, 0, insertion)
+        assert (l, c) == (4, len(insertion))
+        assert new_text == self.TEXT + "\n" + insertion