Fix AlertState.init availability (#198)

In SwiftUI Navigation 1.0, `AlertState` had many initializers to match
the various interfaces in SwiftUI, and they matched the availability of
the SwiftUI interfaces. We simplified to a single interface in 2.0, but
didn't consider the availability mismatch.

While we could bring back the old APIs, it might be nice to favor the
modern builder style. The one caveat is that it will be possible to
render alerts pre-iOS 15 that are configured with more than the maximum
2 buttons at that time. We can emit a runtime warning if we detect this,
but we are losing some of the compile-time check of the previous
version.

Sources/SwiftNavigation/AlertState.swift

@@ -155,7 +155,6 @@ public struct AlertState<Action>: Identifiable {
   ///   - title: The title of the alert.
   ///   - actions: A ``ButtonStateBuilder`` returning the alert's actions.
   ///   - message: The message for the alert.
-  @available(iOS 15, macOS 12, tvOS 15, watchOS 8, *)
   public init(
     title: () -> TextState,
     @ButtonStateBuilder<Action> actions: () -> [ButtonState<Action>] = { [] },

Sources/SwiftUINavigation/Alert.swift

@@ -1,4 +1,5 @@
 #if canImport(SwiftUI)
+  import IssueReporting
   import SwiftUI
 
   @available(iOS 15, macOS 12, tvOS 15, watchOS 8, *)
@@ -214,18 +215,25 @@
     ///   - action: An action handler, called when a button with an action is tapped, by passing the
     ///     action to the closure.
     public init<Action>(_ state: AlertState<Action>, action: @escaping (Action?) -> Void) {
-      if state.buttons.count == 2 {
+      if state.buttons.count <= 1 {
         self.init(
           title: Text(state.title),
           message: state.message.map { Text($0) },
-          primaryButton: .init(state.buttons[0], action: action),
-          secondaryButton: .init(state.buttons[1], action: action)
+          dismissButton: state.buttons.first.map { .init($0, action: action) }
         )
       } else {
+        if state.buttons.count > 2 {
+          reportIssue(
+            """
+            'Alert' handed 'AlertState' with too many buttons. Will only display the first two.
+            """
+          )
+        }
         self.init(
           title: Text(state.title),
           message: state.message.map { Text($0) },
-          dismissButton: state.buttons.first.map { .init($0, action: action) }
+          primaryButton: .init(state.buttons[0], action: action),
+          secondaryButton: .init(state.buttons[1], action: action)
         )
       }
     }
@@ -240,18 +248,25 @@
       _ state: AlertState<Action>,
       action: @escaping @Sendable (Action?) async -> Void
     ) {
-      if state.buttons.count == 2 {
+      if state.buttons.count <= 1 {
         self.init(
           title: Text(state.title),
           message: state.message.map { Text($0) },
-          primaryButton: .init(state.buttons[0], action: action),
-          secondaryButton: .init(state.buttons[1], action: action)
+          dismissButton: state.buttons.first.map { .init($0, action: action) }
         )
       } else {
+        if state.buttons.count > 2 {
+          reportIssue(
+            """
+            'Alert' handed 'AlertState' with too many buttons. Will only display the first two.
+            """
+          )
+        }
         self.init(
           title: Text(state.title),
           message: state.message.map { Text($0) },
-          dismissButton: state.buttons.first.map { .init($0, action: action) }
+          primaryButton: .init(state.buttons[0], action: action),
+          secondaryButton: .init(state.buttons[1], action: action)
         )
       }
     }