Use bytes rather than native string for result (#46281)

This prevents a stack trace in Python 3 when the result is an empty file since
the file is open in binary mode and a native string in Python 3 is str,
not bytes.

changelogs/fragments/blockinfile-bytes-fix.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+  - blockinfile - use bytes rather than a native string to prevent a stacktrace in Python 3 when writing to the file (https://github.com/ansible/ansible/issues/46237)

lib/ansible/modules/files/blockinfile.py

@@ -309,7 +309,7 @@ def main():
         if original is None or original.endswith(b('\n')):
             result += b('\n')
     else:
-        result = ''
+        result = b''
 
     if module._diff:
         diff['after'] = result

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

@@ -16,13 +16,18 @@
 # You should have received a copy of the GNU General Public License
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
-- set_fact: output_dir_test={{output_dir}}/test_blockinfile
+- set_fact:
+    output_dir_test: "{{ output_dir }}/test_blockinfile"
 
 - name: make sure our testing sub-directory does not exist
-  file: path="{{ output_dir_test }}" state=absent
+  file:
+    path: "{{ output_dir_test }}"
+    state: absent
 
 - name: create our testing sub-directory
-  file: path="{{ output_dir_test }}" state=directory
+  file:
+    path: "{{ output_dir_test }}"
+    state: directory
 
 ##
 ## blockinfile
@@ -40,11 +45,19 @@
       Match User ansible-agent
       PasswordAuthentication no
   register: blockinfile_test0
+
 - name: check content
   shell: 'grep -e "Match User ansible-agent" -e "PasswordAuthentication no" {{ output_dir_test }}/sshd_config'
   register: blockinfile_test0_grep
-- debug: var=blockinfile_test0
-- debug: var=blockinfile_test0_grep
+
+- debug:
+    var: blockinfile_test0
+    verbosity: 1
+
+- debug:
+    var: blockinfile_test0_grep
+    verbosity: 1
+
 - name: validate first example results
   assert:
     that:
@@ -61,7 +74,41 @@
       Match User ansible-agent
       PasswordAuthentication no
   register: blockinfile_test1
+
 - name: validate idempotence results
   assert:
     that:
       - 'not blockinfile_test1.changed'
+
+- name: Create a file with blockinfile
+  blockinfile:
+    path: "{{ output_dir_test }}/empty.txt"
+    block: |
+      Hey
+      there
+    state: present
+    create: yes
+  register: empty_test_1
+
+- name: Run a task that results in an empty file
+  blockinfile:
+    path: "{{ output_dir_test }}/empty.txt"
+    block: |
+      Hey
+      there
+    state: absent
+    create: yes
+  register: empty_test_2
+
+- stat:
+    path: "{{ output_dir_test }}/empty.txt"
+  register: empty_test_stat
+
+- name: Ensure empty file was created
+  assert:
+    that:
+      - empty_test_1 is changed
+      - "'File created' in empty_test_1.msg"
+      - empty_test_2 is changed
+      - "'Block removed' in empty_test_2.msg"
+      - empty_test_stat.stat.size == 0