Derived defaults are not updated when referenced property is updated

[lhupfeldt]

Describe the problem

Given the following template config:

_subdirectory: template

a:
  type: str
  default: "a1"

b:
  type: str
  default: "b {{ a }}"

template/{{_copier_conf.answers_file}}.jinja

copier copy <emplate> <dest>

No git tags found in template; using HEAD as ref
🎤 a
   a1
🎤 b
   b a1

cd <dest>
 
copier update --vcs-ref HEAD --data a=a2
Keeping template version 0.0.0.post1.dev0+580c8b4
🎤 b
   b a1

The default for b, if not otherwise changed from the previous default, should be b a2.
The same issue exists if the default for a was changed in a new template version.

This is even more error prone if using --skip-answered

Fixing this may require more meta data in the answers file, so maybe a candidate for the ongoing re-factoring?

Template

copier.yaml:

_subdirectory: template

a:
  type: str
  default: "a1"

b:
  type: str
  default: "b {{ a }}"

and template/{{_copier_conf.answers_file}}.jinja

ps. For some reason I'm unable to upload files.

To Reproduce

No response

Logs

Expected behavior

Derived default property values are updated when property values which they are derived from are updated.

Screenshots/screencasts/logs

No response

Operating system

Linux

Operating system distribution and version

Fedora 44

Copier version

9.15.1

Python version

3.14.4

Installation method

pip+pypi

Additional context

No response

[sisp]

I don't think that your expected behavior is how it should be. Once answers have been recorded in the answers file, they take precedence over default answers when updating a project. I think this behavior is intuitive and expected. Perhaps you could use a computed value to achieve your expected behavior?

 _subdirectory: template

 a:
   type: str
   default: "a1"

 b:
   type: str
   default: "b {{ a }}"
+  when: false

[lhupfeldt]

Sorry for my late reply.
I have thought about using when: false (we use it a lot already) but I'm not sure it applies to all my use cases.
Actually I think the feature I want i broader then the describe scenario.
I want to be able to upgrade with any changed default value regardless if it is a derived property or not. I.e. if the default value of a is changed I want to update all subprojects using the default.
This would be a breaking change, so would probably need a new options --update-to-new-defaults.