Keep single-line array bracket off a trailing comment line

tests/test_items.py

@@ -529,6 +529,16 @@ def test_array_add_line() -> None:
     )
 
 
+def test_array_add_line_single_line_comment_round_trips() -> None:
+    # A single-line array whose last rendered element is a trailing comment
+    # (from add_line(..., comment=...)) must keep the closing bracket off the
+    # comment line, otherwise the output does not round-trip (GH #580).
+    t = api.array()
+    t.add_line("foo", comment="bar")
+    rendered = t.as_string()
+    assert parse("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 +1464,14 @@ 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())}]"
+            rendered = list(self._iter_items())
+            inner = "".join(v.as_string() for v in rendered)
+            if rendered and isinstance(rendered[-1], Comment):
+                # A trailing comment (e.g. from add_line(comment=...)) carries
+                # no newline, so keep the closing bracket off the comment line
+                # to produce parseable output (GH #580).
+                inner += "\n" + self.trivia.indent
+            return f"[{inner}]"
 
         s = "[\n"
         s += "".join(