# `layout.unused_declaration`

Shared declaration is not used.

Area 1, [Project layout and modules](/docs/project-layout-and-modules.md); not declinable; the next step is usually the agent's.

```jadpo
type DueWindow = Int {
    min: 1
}
```

```text
error: `DueWindow` isn't used
 --> domains/planning/types/due_window.jadpo:1:6
  |
1 | type DueWindow = Int {
  |      ^^^^^^^^^ nothing uses this
  reason: A shared type exists to be used by several files; one that nothing uses is dead code. Tests don't count as users.
  next: Use `DueWindow`, or remove it if nothing will (agent)
  rule: layout.unused_declaration
  help: https://jadpo.dev/docs/errors/layout.unused_declaration

check failed: 1 error, 2 files
```

Beside a file's primary declaration, a supporting type or helper is there
for it: the primary uses it, directly or through another supporting
declaration it uses. One only the file's tests use is dead code too:


```jadpo
type Shelf = Int {
    min: -2
    max: 2
}

type OvenTemperature = Int {
    min: 0
    max: 300
}

function top_shelf() -> Shelf {
    return 2
}

/// The temperature for a bake on `shelf`: a high shelf runs hot.
action set_oven(shelf: Shelf) -> OvenTemperature {
    if (shelf > 0) {
        return 190
    }
    return 200
}
```

```text
error: `top_shelf` isn't used by `set_oven`
 --> domains/kitchen/actions/set_oven.jadpo:11:10
   |
11 | function top_shelf() -> Shelf {
   |          ^^^^^^^^^ `set_oven` doesn't use this
  reason: Everything in a file besides the declaration it is named after is there for that declaration, used by it directly or through one another; anything else is dead code. Tests don't count as users.
  next: Use `top_shelf` in `set_oven`, or remove it if nothing will (agent)
  rule: layout.unused_declaration
  help: https://jadpo.dev/docs/errors/layout.unused_declaration

check failed: 1 error, 3 files
```

The file's test calls `top_shelf`, which doesn't count:

```jadpo
test "the top shelf is turned down" {
    assert set_oven(top_shelf()) == 190
}
```

A type written ahead of what will use it is refused the same way. Write it
and its first user as one change, then check:


```jadpo
type DueWindow = Int {
    min: 1
}
```

```jadpo
use planning/types { DueWindow }

/// The window a reminder waits, as it was asked for.
action next_due(days: DueWindow) -> DueWindow {
    return days
}
```