Remove support for this.attrs

text/1016-deprecate-this-attrs-in-templates.md

@@ -0,0 +1,61 @@
+---
+stage: accepted
+start-date: 2020-12-22T00:00:00.000Z
+release-date: 2021-03-22T00:00:00.000Z
+release-versions:
+  ember-source: v3.26.0
+
+teams:
+  - framework
+prs:
+  accepted: https://github.com/emberjs/rfcs/pull/1016 
+project-link:
+---
+
+# Deprecate using `{{attrs}}` and {{this.attrs}} in templates
+
+## Summary
+
+[RFC #690](https://github.com/emberjs/rfcs/pull/690) had some unfortunate timing where `{{attrs}}` was widely used, but before usage of `{{this.x}}` became widely common. As such, the deprecation messaging [implemented here](https://github.com/emberjs/ember.js/blob/0822efd9c0554f11d01232585596ac70c14a4306/packages/ember-template-compiler/lib/plugins/assert-against-attrs.ts#L58) only messaged in the case of `{{attrs}}`, rather than both `{{attrs}}` and `{{this.attrs}}`. 
+
+
+The RFC had intended, and even describes in its transition path to move away from `{{this.attrs}}`. [The code for the build time assertion](https://github.com/emberjs/ember.js/blob/0822efd9c0554f11d01232585596ac70c14a4306/packages/ember-template-compiler/lib/plugins/assert-against-attrs.ts#L84) even tried to handle the `{{this.attrs}}` case. 
+
+
+```hbs
+{{attrs.foo}} and {{this.attrs.foo}}
+
+{{! is equivalent to }}
+{{@foo}} and {{@foo}}
+```
+
+It was a legacy API that existed prior to named arguments being introduced in
+Ember, and has continued to be supported via a template transform for some time.
+
+This RFC proposes that we add a deprecation warning to the build-time assertion that forbids `{{attrs}}`, it will also forbid `{{this.attrs}}`. 
+
+## Motivation
+
+The `{{attrs}}` / `{{this.attrs}}` syntax was from a previous iteration of the concepts that
+eventually became named argument syntax. Now that named arguments exist in the
+framework, and are considered the best practice, there is no reason to continue
+supporting this syntax.
+
+## Transition Path
+
+Users who currently rely on referencing `{{attrs}}` or `{{this.attrs}}` can convert their references
+to named arguments.
+
+## How We Teach This
+
+### Deprecation Guide
+
+The deprecation guide from [3.26.0](https://deprecations.emberjs.com/v3.x#toc_attrs-arg-access) is already sufficient.
+
+## Alternatives
+
+pre-v6 deprecation.
+
+## Drawbacks
+
+- None