# LS2017: LiteSpecLayer Names No Known Layer

## Intent

LS2017 is a compiler check that reports a `LiteSpecLayer` project value naming no known layer under the `layer-projects` extension, so a misspelled value cannot silently turn the analyzers off. This page states what the rule reports, where the error sits, and how to name the layer.

## Reference

### What the Rule Enforces

LS2017 enforces [Use Five Application Projects](https://litespec.dev/4.0.0/backend/dotnet/ext/layer-projects.md#use-five-application-projects) (`litespec/backend/dotnet/ext/layer-projects#use-five-application-projects`). It runs in every project that declares `LiteSpecLayer`, whatever the value. Its category is `LiteSpec.Layers`. Severity and enablement follow the [Analyzers overview](https://litespec.dev/4.0.0/analyzers/README.md).

### What the Rule Reports

The rule reports a declared `LiteSpecLayer` value that names no known layer: anything but `Domain`, `Application.Abstractions`, `Application`, `Infrastructure`, `WebApi`, `Worker`, `Test`, `Tests`, or `None`, ignoring dots and case. The diagnostic sits on the first token of the first file, and its message names the declared value and the accepted names.

### Failing Example

```csharp
namespace Shop.Billing;

internal sealed class ChargeDuesJob
{
}
```

with `<LiteSpecLayer>Staging</LiteSpecLayer>` in the project file.

### Passing Example

```csharp
namespace Shop.Billing;

internal sealed class ChargeDuesJob
{
}
```

with `<LiteSpecLayer>Worker</LiteSpecLayer>` in the project file.

### How to Fix

Set `LiteSpecLayer` to the layer the project holds, or to `None` to opt the project out. Under the default module layout the analyzers read each file's layer from its folder, so `LiteSpecLayer` has no effect there.

## Notes

### What the Rule Ignores

The rule does not report a project that declares no `LiteSpecLayer` value: without the property the analyzers read the assembly name suffix under `layer-projects`. It does not report the `None` value, which opts the project out on purpose.