fi-0077: Interaction payload cannot be empty struct {:#fi-0077}

The payloads in a method or event cannot be empty structs:

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

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0077-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0077-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

If you would like to express that a particular request/response does not hold any information, delete the empty struct, leaving () in that location:

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

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0077-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0077-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

Empty structs cannot be extended, and take 1 byte on the wire. Since FIDL supports interactions without payloads, using empty structs this way is superfluous and less efficient. Therefore they are not allowed.