This deprecates the `apis.Immutable` and `apis.Annotatable` interfaces,
which were both awkward niche extensions of `apis.Validatable` and
`apis.SetDefaults` for specific contexts that the former set didn't
cover well.
With this change, the expectation is that types that want to check
for immutability will instead access the "baseline" object via the
context from within updates. For example:
```
func (new *Type) Validate(ctx context.Context) *apis.FieldError {
if apis.IsInUpdate(ctx) {
old := apis.GetBaseline(ctx).(*Type)
// Update specific validation based on new and old.
}
}
```
For applying user annotations, the type writer can write:
```
func (new *Type) SetDefaults(ctx context.Context) {
if apis.IsInCreate(ctx) {
ui := apis.GetUserInfo(ctx)
// Set creator annotation from ui
}
if apis.IsInUpdate(ctx) {
ui := apis.GetUserInfo(ctx)
old := apis.GetBaseline(ctx).(*Type)
// Compare old.Spec vs. new.Spec and on changes
// update the "updater" annotation from ui.
}
}
```
One of the key motivations for this refactoring was to enable us
to do more powerful validation in `apis.Validate` beyond the niche
of immutability checking (and without introducing yet-another
one-off niche interface). In the BYO Revision name PoC I abused
`apis.Immutable` to do more arbitrary before/after validation,
which with this can simply be a part of `apis.Validatable`.
See: https://github.com/knative/serving/pull/3562
The general stance on deprecating interfaces such as these will be
to deprecate them in a non-breaking way (via a comment for now). They
will be hollowed out when the functionality is removed from the webhook,
but left in because of diamond dependency problems. In this change
we remove the `apis.Annotatable` functionality and deprecate the
`apis.Immutable` functionality.
Matt Moore