swift-mirror/userdocs/diagnostics/useless-availability-check.md

Useless availability check (UselessAvailabilityCheck)

Warnings that identify if #available queries that are guaranteed to succeed because an enclosing scope already restricts availability.

Overview

When an if #available query checks for an availability that is already implied by the availability of an enclosing scope (such as a containing declaration's @available attribute or another if #available block), the check is unnecessary and the guard will always succeed at runtime.

@available(macOS 26.4, *)
struct WeatherView: View {
  var body: some View {
    if #available(macOS 26.0, *) { // warning: unnecessary check for 'macOS'; enclosing scope ensures guard will always be true
      // ...
    }
  }
}

The if #available check above can be removed because WeatherView is already restricted to macOS 26.4 or newer, which implies macOS 26.0 or newer.