From 3ffd6aeca62ac65275d6ad089bb837a9eba4cfb2 Mon Sep 17 00:00:00 2001
From: Vincent Gao <gaobing1230@gmail.com>
Date: Mon, 22 Jun 2026 11:25:47 +0200
Subject: [PATCH] Preserve table display names on self assignment

---
 CHANGELOG.md                |  1 +
 tests/test_toml_document.py | 14 ++++++++++++++
 tomlkit/container.py        |  2 +-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index faad379..4d2be26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,7 @@
 - Fix a `KeyAlreadyPresent` error when parsing or accessing an out-of-order table whose array-of-tables elements are split across the table's parts. ([#505](https://github.com/python-poetry/tomlkit/issues/505))
 - Out-of-order value-vs-table and dotted-key-vs-table redefinitions are now rejected at parse time instead of being silently accepted or raising only on access. The parser also detects when a non-dotted key is a prefix of an existing dotted key, matching the stdlib `tomllib` behaviour. ([#523](https://github.com/python-poetry/tomlkit/issues/523))
 - Reject tables inserted into inline tables instead of serializing invalid TOML. ([#531](https://github.com/python-poetry/tomlkit/issues/531))
+- Fix a table's display name (its exact header spelling, including whitespace and quoting) being normalised when the table is assigned onto itself, e.g. `doc[k] = doc[k]` rewriting `[keys .'a'.'c']` to `[keys.a.'c']`. ([#291](https://github.com/python-poetry/tomlkit/issues/291))
 
 ## [0.15.0] - 2026-05-10
 
diff --git a/tests/test_toml_document.py b/tests/test_toml_document.py
index a1eea7a..36ac0de 100644
--- a/tests/test_toml_document.py
+++ b/tests/test_toml_document.py
@@ -1024,6 +1024,20 @@ def test_replace_super_table_preserves_whitespace() -> None:
     assert doc.as_string() == content
 
 
+def test_replace_table_with_itself_preserves_display_name() -> None:
+    content = """\
+[keys.a]
+[keys .'a'.'c']
+  'd'	= 'e'
+"""
+    doc = parse(content)
+
+    for mode in doc["keys"]:
+        doc["keys"][mode] = doc["keys"][mode]
+
+    assert doc.as_string() == content
+
+
 def test_replace_with_table_of_nested() -> None:
     example = """\
     [a]
diff --git a/tomlkit/container.py b/tomlkit/container.py
index 0494019..310a502 100644
--- a/tomlkit/container.py
+++ b/tomlkit/container.py
@@ -928,7 +928,7 @@ def _replace_at(
                 value.trivia.trail = v.trivia.trail
             self._body[idx] = (new_key, value)
 
-        if hasattr(value, "invalidate_display_name"):
+        if value is not v and hasattr(value, "invalidate_display_name"):
             value.invalidate_display_name()
 
         if isinstance(value, Table):