Fix single-line Array losing its closing bracket after a trailing comment

tests/test_items.py

@@ -559,6 +559,17 @@ def test_array_add_line() -> None:
     )
 
 
+def test_array_add_line_with_comment_on_last_line_round_trips() -> None:
+    # A trailing comment on the last (and only) line of a non-multiline array
+    # used to swallow the closing bracket, since "#" comments run to the end
+    # of the physical line and nothing forced a newline before the "]".
+    t = api.array()
+    t.add_line("foo", comment="bar")
+    rendered = t.as_string()
+    assert rendered == '[\n    "foo", # bar\n]'
+    assert parse(f"a = {rendered}")["a"] == ["foo"]
+
+
 def test_array_add_line_multiline_comment_is_rejected() -> None:
     t = api.array()
     with pytest.raises(ValueError, match="line breaks"):

tomlkit/items.py

@@ -1464,7 +1464,18 @@ def multiline(self, multiline: bool) -> Array:
 
     def as_string(self) -> str:
         if not self._multiline or not self._value:
-            return f"[{''.join(v.as_string() for v in self._iter_items())}]"
+            s = "".join(v.as_string() for v in self._iter_items())
+            # A trailing "# ..." comment swallows anything that follows it on
+            # the same line, including the closing bracket. If the rendered
+            # content ends with a comment that isn't already followed by a
+            # newline, force one so the array still round-trips as valid TOML.
+            if (
+                self._value
+                and self._value[-1].comment is not None
+                and not s.endswith(("\n", "\r"))
+            ):
+                s += "\n" + self.trivia.indent
+            return f"[{s}]"
 
         s = "[\n"
         s += "".join(