Move HTTP Mock to addon

text/0000-http-mock.md

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+- Start Date: 2020-01-09
+- Relevant Team(s): Ember CLI
+- RFC PR: https://github.com/emberjs/rfcs/pull/576
+- Tracking:
+
+# Move http-mock feature into addon
+
+## Summary
+
+This RFC proposes to remove the builtin generator for `http-mock` feature in Ember CLI and move the
+feature into an addon.
+
+## Motivation
+
+Removing the `http-mock` feature from the core offering of Ember CLI is an easy way to reduce the
+Ember and Ember CLI surface area. Additionally `ember-cli-mirage` has become the standard addon to
+mock server responses for testing and development and removing http-mock would make it more clear
+that the Ember build system can be compatible with more than one solution to server mocking.
+
+## Detailed design
+
+Extract the http-mock generator into an addon and remove documentation from https://ember-cli.com/user-guide/#mocks
+
+## How we teach this
+
+There shouldn't be much to teach with this removal because the feature is not used very often and
+removing it should not need teaching.
+
+## Drawbacks
+
+- There are some concerns about Mirage slowing down a test suite because it can generate many objects
+at setup time.
+    - A lot of this bottleneck comes from using Mirage Models / Ember Data. It's possible that working
+    with the authors to improve that performance or recommending that the default experience is to
+    use plain JSON responses would mitigate this issue.
+
+## Alternatives
+
+Leave it in.
+
+## Unresolved questions
+
+- How does the `ember server` command use the output of the `server/` directory generated by http-mock
+and does any code need to be cleaned up and moved into the addon there? Will any new public APIs need
+to be introduced for an addon to implement the same feature?