docs/reference/fidl/language/error-catalog/_fi-0042.md

## fi-0042: Duplicate library import {:#fi-0042}

Dependencies cannot be imported multiple times:

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

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0042-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0042-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

Ensure that each dependency is only imported once:

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

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0042-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0042-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

It is worth noting that FIDL does not support importing different versions of
the same library. The `@available` version is resolved for the entire `fidlc`
compilation via the `--available` flag, meaning that both the library being
compiled and all of its dependencies must share the same version for any given
compilation run.