blockinfile - fix line end regression (#69734)

PR #66461 introduced a regression that resulted in an in correct block in the file
if the block to be inserted did not end with a line separator. Fix this bug and add
tests to cover this scenario.

changelogs/fragments/blockinfile-line-ending-fix.yaml

@@ -0,0 +1,4 @@
+bugfixes:
+  - >
+    blockinfile - fix regression that results in incorrect block in file when the
+    block to be inserted does not end in a line separator (https://github.com/ansible/ansible/pull/69734)

lib/ansible/modules/blockinfile.py

@@ -272,6 +272,8 @@ def main():
         # Escape sequences like '\n' need to be handled in Ansible 1.x
         if module.ansible_version.startswith('1.'):
             block = re.sub('', block, '')
+        if not block.endswith(b(os.linesep)):
+            block += b(os.linesep)
         blocklines = [marker0] + block.splitlines(True) + [marker1]
     else:
         blocklines = []

test/integration/targets/blockinfile/tasks/main.yml

@@ -137,3 +137,35 @@
       - 'blockinfile_test2 is changed'
       - 'blockinfile_test2.msg == "Block inserted"'
       - 'blockinfile_test2_grep.stdout == "6"'
+
+
+- name: Add block without trailing line separator
+  blockinfile:
+    path: "{{ output_dir_test }}/chomped_block_test.txt"
+    create: yes
+    content: |-
+      one
+      two
+      three
+  register: chomptest1
+
+- name: Add block without trailing line separator again
+  blockinfile:
+    path: "{{ output_dir_test }}/chomped_block_test.txt"
+    content: |-
+      one
+      two
+      three
+  register: chomptest2
+
+- name: Check output file
+  stat:
+    path: "{{ output_dir_test }}/chomped_block_test.txt"
+  register: chomptest_file
+
+- name: Ensure chomptest results are correct
+  assert:
+    that:
+      - chomptest1 is changed
+      - chomptest2 is not changed
+      - chomptest_file.stat.checksum == '50d49f528a5f7147c7029ed6220c326b1ee2c4ae'