[DEPRECATION RFC ember-data] deprecate errors changing record state

text/0000-ember-data-deprecate-errors-changing-valid-state.md

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+- Start Date: 2018-10-04
+- RFC PR: (leave this empty)
+- Ember Issue: (leave this empty)
+
+# Ember Data | Deprecate Errors changing record-state
+
+## Summary
+
+Deprecates the `add` `remove` and `clear` methods of `DS.Errors` in favor of `addError`
+ `removeError` and `clearErrors`.
+
+## Motivation
+
+In `ember-data`, adding, removing, or clearing errors from a record's `errors` object
+ will affect the validation state of the record. Previously a [soft-deprecation](https://github.com/emberjs/data/pull/3853) of
+ this behavior was added; however, it provided no clear path to resolution. 
+
+By deprecating these methods entirely, and providing replacement methods that do not
+ affect the state of the `record`, we provide end users a clear path and a clear timeline
+ for resolving the deprecation, and a mechanism through which users can determine if this
+ change in behavior requires any additional changes in their application code.
+
+## Detailed design
+
+The warnings in `DS.Errors` `add` `remove` and `clear` will be upgraded to deprecations
+ targeting the next LTS `3.8`. This means the feature and these methods will be removed
+ in `3.9`.
+
+New methods will be added to `DS.Errors` that do not affect record state. `addErrors` `removeErrors`
+ and `clearErrors`. These methods will have the same signatures as before, listed below, where
+ `member` is one of `type` `id` or the property name of an `attribute` or `relationship`.
+
+```typescript
+interface Errors {
+  addErrors(member: string, messages: string|Array<string>): void;
+  removeErrors(member: string): void;
+  clearErrors(): void;
+}
+```
+
+## How we teach this
+
+`DS.Errors` is not well documented today, so this is an opportunity for us to revisit and
+ clean up.
+
+## Drawbacks
+
+- For apps using `Errors` that do not rely on the changes to record state, this will feel like
+ unnecessary churn.
+- The new method names may feel unnecessarily verbose
+
+## Alternatives
+
+Two alternatives were considered:
+
+1) upgrading the existing warning to specify that the behavior would be removed in `3.9`,
+   We felt this was equally un-actionable as the state of things today.
+2) treating the warning as a fully complete deprecation, and removing the undesired behavior now,
+   as the warning has been in place long enough to be considered "complete" post the `3.4 lts` cycle.
+   We felt this was unfair to consumers who have had no way to act upon the deprecation or determine
+   if it would have any effects on their applications.
+
+## Unresolved questions
+
+None