`juju deploy --dry-run` reporting false positives for config changes

So one question is whether the default value for ppa is
ppa:ua-client/stable, in which case we are distinguishing from a charm
explicitly setting the value to what happens to be the default, vs just
inheriting the default value.

On Sat, Apr 24, 2021 at 5:00 AM Tom Haddon <email address hidden>
wrote:

> Public bug reported:
>
> When running `juju deploy --dry-run` I'm seeing false positives for config
> differences. The output of `juju config ubuntu-advantage ppa` is
> `ppa:ua-client/stable`, but when I run juju deploy --dry-run --verbose
> against my bundle file I see:
> ```
> Changes to deploy bundle:
> - set application options for ubuntu-advantage
> setting options:
> ppa: "ppa:ua-client/stable"
> ```
> Here's some more verbose output (sorry, Canonical only):
>
> https://pastebin.canonical.com/p/hpN6Jd948J/
>
> ** Affects: juju
> Importance: Undecided
> Status: New
>
> --
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> Matching subscriptions: juju bugs
> https://bugs.launchpad.net/bugs/1925998
>
> Title:
> `juju deploy --dry-run` reporting false positives for config changes
>
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>

The charm default is indeed `ppa:ua-client/stable` and `juju config ubuntu-advantage` is reports `source: default`. So it sounds like this is as you say the difference between being left to the charm default and set explicitly to the same value as the charm default. Seems we can close this out. Thanks.

The behavior of juju 2.9.22 is now different. You cannot explicitly set a variable to the same value as default for the charm:

to demonstrate:

$ juju deploy ubuntu
$ juju config ubuntu hostname=""
WARNING the configuration setting "hostname" already has the value ""
$ juju config ubuntu
*snip*
settings:
  hostname:
    default: ""
    description: Override hostname of machine, when empty uses default machine hostname
    source: default
    type: string
    value: ""

Note that the source remains default, and the user cannot explicitly set the value any longer. This protects against bundles that overly zealously configure charm settings which are default, but doesn't protect against charm authors potentially changing charm defaults in the future when users would prefer to nail their configs to the current defaults as they upgrade their charm.

Unable to replicate this. Presumably it was resolved by accident?

```
$ juju version
2.9.40-ubuntu-amd64

$ juju config ubuntu hostname
foo.bar

$ cat bundle.bundle
series: focal
applications:
  ubuntu:
    charm: ubuntu
    channel: stable
    revision: 21
    num_units: 1
    to:
    - "0"
    options:
      hostname: foo.bar
    constraints: arch=amd64
machines:
  "0":
    constraints: arch=amd64

$ juju deploy ./bundle.bundle --dry-run --verbose
No changes to apply.
```

Closing this. Feel free to re-open if you are still able to replicate