Deprecate Component#isVisible

text/0000-deprecate-component-isvisible.md

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+- Start Date: 2018-03-28
+- RFC PR:
+- Ember Issue:
+
+# Summary
+
+The aim of this RFC is to deprecate the component's `isVisible` property. 
+It is not used by Ember internally and left undefined unless manually set.
+It's poorly documented and component visibility it better managed in 
+template space rather than JS.
+
+# Motivation
+
+Setting the isVisible property on a component instance as a way to toggle
+the visibility of the component is confusing. The majority of its usage
+predates even Ember 1.0.0, and modern Ember applications already completely
+avoid using isVisible in favor of simpler conditionals in the template
+space.
+
+In addition, when `isVisible` is used today it often introduces subtle (and
+difficult to track down) bugs due to its interaction with the `style`
+attribute (toggling `isVisible` clobbers any existing content in `style`).
+
+Simply put, removing `isVisible` will reduce confusion amongst users.
+
+# Transition Path
+
+Whenever `isVisible` is used a deprecation will be issued with a link to 
+the deprecation guide explaining the deprecation and how to refactor in order
+to avoid it.
+
+Given that `Component#isVisible` is a public API, deprecating now would
+schedule for removal in the next major version release (4.0).
+
+There are several options available to hiding elements 
+such as `<div hidden={{boolean}}></div>`(hidden is valid for all elements
+and is semantically correct) or wrapping the component in a template
+conditional `{{#if}}` statement. Components `classNames` and `classNameBindings`
+could also be used to add hidden classes.
+
+# How We Teach This
+
+The `isVisible` property is rarely used, the deprecation along with a mention
+in a future blog post would be sufficient.
+
+We should consider adding documentation on hiding components to the Ember
+guides with the conditional handlebar helper or via the widely supported `hidden`
+attribute.
+
+```hbs
+{{#if showComponent}}
+  {{component}}
+{{/if}}
+
+{{! or }}
+<div hidden={{isHidden}}></div>
+```
+
+# Alternatives
+
+An alternative option would be to to keep `isVisible`.