Emptying a nested array of tables before an out-of-order super-table renders invalid TOML (0.15.2, since #567) #690

Versions tested: tomlkit 0.15.2 (tag a0b15eb), and master at d7def7d (2026-10-29); Python 3.12.

Reproduce:

import tomlkit

doc = tomlkit.parse("[[a.b.c]]\nx = 1\n\n[a]\ny = 1\n")
doc["a"]["b"]["c"].pop()
out = tomlkit.dumps(doc)
print(repr(out))
tomlkit.parse(out)

The input is valid TOML, and tomlkit parses it to {'a': {'b': {'c': [{'x': 1}]}, 'y': 1}}. After the pop, doc.unwrap() is {'a': {'b': {'c': []}, 'y': 1}}, as expected.

Observed: dumps returns 'a.b.c = []\n[a]\ny = 1\n', which declares a twice:

tomlkit.exceptions.ParseError: Redefinition of an existing table at line 3 col 0

tomllib.loads rejects it too: Cannot declare ('a',) twice (at line 2, column 3).

Expected: output that parses back to {'a': {'b': {'c': []}, 'y': 1}}, for example what tomlkit.dumps(doc.unwrap()) returns:

[a]
y = 1

[a.b]
c = []

Where it comes from: #567 renders an emptied array of tables as key = []. When the array sits under a super-table that is defined later in the document, the dotted key is emitted where the [[a.b.c]] header was, before [a]. On the parent commit of #567, the same steps produce output that parses. The same happens when [a] extends a.b with a dotted key, for example [[a.b.c]]\nx = 1\n[a]\nb.z = 1\n.

Related: #553, which #567 addressed in part, and #675, another failure after removing an element from an out-of-order table.

This came up while running generated tests on pairs of tomlkit pull requests that were open at the same time (#565 and #567). The reproduction above gives the same output on 0.15.2 and on master.