[PR #12148/5004c9f7 backport][stable-12] xml: preserve DOCTYPE declaration when writing XML files (#12248)

xml: preserve DOCTYPE declaration when writing XML files (#12148)

* fix(xml): preserve DOCTYPE declaration when writing XML files

Pass `doctype=tree.docinfo.doctype` to all `ElementTree.write()` calls
so lxml does not silently drop the DOCTYPE on serialization. Also replace
`etree.tostring()` with BytesIO+write() in the diff and xmlstring paths
for consistency.

Fixes #2762



* test(xml): add integration test for DOCTYPE preservation



* feat(changelog): add fragment for xml DOCTYPE fix (#12148)



---------


(cherry picked from commit 5004c9f70f)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/integration/targets/xml/fixtures/ansible-xml-doctype.xml

@@ -0,0 +1,3 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE foo SYSTEM "foo.dtd">
+<foo value="0"/>

tests/integration/targets/xml/fixtures/ansible-xml-doctype.xml.license

@@ -0,0 +1,3 @@
+GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+SPDX-License-Identifier: GPL-3.0-or-later
+SPDX-FileCopyrightText: Ansible Project

tests/integration/targets/xml/results/test-preserve-doctype.xml

@@ -0,0 +1,3 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE foo SYSTEM "foo.dtd">
+<foo value="1"/>

tests/integration/targets/xml/results/test-preserve-doctype.xml.license

@@ -0,0 +1,3 @@
+GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+SPDX-License-Identifier: GPL-3.0-or-later
+SPDX-FileCopyrightText: Ansible Project

tests/integration/targets/xml/tasks/main.yml

@@ -78,6 +78,7 @@
     - include_tasks: test-print-match.yml
     - include_tasks: test-xmlstring.yml
     - include_tasks: test-children-elements-xml.yml
+    - include_tasks: test-preserve-doctype.yml
 
     # Unicode tests
     - include_tasks: test-add-children-elements-unicode.yml

tests/integration/targets/xml/tasks/test-preserve-doctype.yml

@@ -0,0 +1,46 @@
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+- name: Setup test fixture
+  copy:
+    src: fixtures/ansible-xml-doctype.xml
+    dest: /tmp/ansible-xml-doctype.xml
+
+- name: Set '/foo/@value' to '1' (file has DOCTYPE)
+  xml:
+    path: /tmp/ansible-xml-doctype.xml
+    xpath: /foo
+    attribute: value
+    value: "1"
+  register: set_attribute_doctype
+
+- name: Add trailing newline
+  shell: echo "" >> /tmp/ansible-xml-doctype.xml
+
+- name: Compare to expected result
+  copy:
+    src: results/test-preserve-doctype.xml
+    dest: /tmp/ansible-xml-doctype.xml
+  check_mode: true
+  diff: true
+  register: comparison
+
+- name: Test expected result (DOCTYPE is preserved)
+  assert:
+    that:
+      - set_attribute_doctype is changed
+      - comparison is not changed
+
+- name: Set '/foo/@value' to '1' again (idempotency)
+  xml:
+    path: /tmp/ansible-xml-doctype.xml
+    xpath: /foo
+    attribute: value
+    value: "1"
+  register: set_attribute_doctype_idempotent
+
+- name: Test idempotency
+  assert:
+    that:
+      - set_attribute_doctype_idempotent is not changed