fi-0071: Unknown attribute disallowed on strict enum members {:#fi-0071}

A strict enum must not have any members annotated with the @unknown attribute:

{% include “docs/reference/fidl/language/error-catalog/label/_bad.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0071.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

To continue using the @unknown attribute, change to a flexible enum:

{% include “docs/reference/fidl/language/error-catalog/label/_good.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0071-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

Otherwise, just remove the attribute altogether to remain a strict enum:

{% include “docs/reference/fidl/language/error-catalog/label/_good.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0071-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

The purpose of the @unknown attribute is to smooth over a transition from a strict enum with a user-defined unknown value, like this into a flexible enum with unknown values known to and handled by FIDL. In the above example, it would be used to transition from the second correct usage to the first one.