Ansible - Append Item to List that's Buried within Dictionary - list

Question

Objective
I am trying to append a string to a list belonging to a key which is a few layers down within a dictionary.
Explanation
I initialize an empty list buried within some pre-existing variable called info:
tasks:
- set_fact:
info: "{{ info | combine( { host: { repo: { folders: [] }}}, recursive=true ) }}"
In a later task, I wish to append a string to that empty list. This may happen over multiple tasks, so I don't want to replace the empty list, but add onto it as needed. I am currently trying this:
tasks:
- set_fact:
info: "{{ info | combine( { 'host': { 'repo': { 'folders': [] }}}, recursive=true ) }}"
- set_fact:
info: "{{ info.host.repo.folders + ['ERROR. folderX does not exist'] }}"
when: folderX does not exist
- set_fact:
info: "{{ info.host.repo.folders + ['ERROR. folderY does not exist'] }}"
when: folderY does not exist
However, I receive a template error:
FAILED! => {"msg": "template error while templating string: expected name or number. String: {{ info.host.repo.folder + ['ERROR. folderX does not exist'] }}"}
I know that you can simply add elements to a list when the destination is on topmost layer. For example:
- set_fact:
folders: []
- set_fact:
folders: "{{ folders + ['ERROR. folderX does not exist'] }}"
when: folderX does not exist
- set_fact:
folders: "{{ folders + ['ERROR. folderY does not exist'] }}"
when: folderY does not exist
- debug: var=folders
Which, as desired, gives:
TASK [debug] ***************************************************************************************************
"folders": [
"ERROR. folderX does not exist",
"ERROR. folderY does not exist"
]
So, how does the syntax change when I am trying to descend multiple layers and access a list that resides in a nested dictionary? Thank you!

Answer 1

dicts and lists in ansible are "live", so you can update them via set statements
- set_fact:
info: >-
{%- set _ = info.host.repo.update({"folders": []}) -%}
{{ info }}
- set_fact:
info: >-
{%- set _ = info.host.repo.folders.append("ERROR. folderY does not exist") -%}
{{ info }}
when: folderY does not exist
that set _ = business is because ansible's jinja does not support the do statement so one cannot have an assignment statement by itself