Conditionals: EitherView and OptionalView with reactive branch visibility

Tests/PorticoTests/ConditionalTests.swift

@@ -0,0 +1,168 @@
+import Testing
+@_spi(SGTKInternal) import Gtk
+@_spi(Portico) import Portico
+
+@MainActor @Suite(.serialized) struct ConditionalTests {
+
+    // MARK: - EitherView
+
+    @Test func eitherViewInitiallyTrueBranch() {
+        guard Gtk.initCheck() else { return }
+        ConditionProbe.reset()
+
+        let box = StateBox(true)
+        let binding = Binding(box)
+        let view = EitherView(binding,
+            first: { FirstProbeLabel() },
+            second: { SecondProbeLabel() }
+        )
+        let widget = AnyView(view).makeWidget(MountContext())
+        let stack = widget as! Gtk.Stack
+
+        // Initially, only the "true" branch is mounted and visible.
+        #expect(stack.getVisibleChildName() == "true")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 0)
+
+        // Toggle to false — lazy-mounts the "false" branch.
+        box.set(false)
+        #expect(stack.getVisibleChildName() == "false")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 1)
+
+        // Toggle back to true — no new mounts.
+        box.set(true)
+        #expect(stack.getVisibleChildName() == "true")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 1)
+    }
+
+    @Test func eitherViewInitiallyFalseBranch() {
+        guard Gtk.initCheck() else { return }
+        ConditionProbe.reset()
+
+        let box = StateBox(false)
+        let binding = Binding(box)
+        let view = EitherView(binding,
+            first: { FirstProbeLabel() },
+            second: { SecondProbeLabel() }
+        )
+        let widget = AnyView(view).makeWidget(MountContext())
+        let stack = widget as! Gtk.Stack
+
+        // Initially, only the "false" branch is mounted and visible.
+        #expect(stack.getVisibleChildName() == "false")
+        #expect(ConditionProbe.firstCount == 0)
+        #expect(ConditionProbe.secondCount == 1)
+
+        // Toggle to true — lazy-mounts the "true" branch.
+        box.set(true)
+        #expect(stack.getVisibleChildName() == "true")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 1)
+
+        // Toggle back to false — no new mounts.
+        box.set(false)
+        #expect(stack.getVisibleChildName() == "false")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 1)
+    }
+
+    @Test func eitherViewTracksConditionChanges() {
+        guard Gtk.initCheck() else { return }
+        ConditionProbe.reset()
+
+        let box = StateBox(true)
+        let binding = Binding(box)
+        let view = EitherView(binding,
+            first: { FirstProbeLabel() },
+            second: { SecondProbeLabel() }
+        )
+        let widget = AnyView(view).makeWidget(MountContext())
+        let stack = widget as! Gtk.Stack
+
+        // Three toggles: true→false→true→false
+        box.set(false)
+        box.set(true)
+        box.set(false)
+
+        #expect(stack.getVisibleChildName() == "false")
+        #expect(ConditionProbe.firstCount == 1)
+        #expect(ConditionProbe.secondCount == 1)
+    }
+
+    // MARK: - OptionalView
+
+    @Test func optionalViewMountsChildOnce() {
+        guard Gtk.initCheck() else { return }
+        ConditionProbe.reset()
+
+        let box = StateBox(true)
+        let binding = Binding(box)
+        let view = OptionalView(binding) { FirstProbeLabel() }
+        let widget = AnyView(view).makeWidget(MountContext())
+        let revealer = widget as! Gtk.Revealer
+
+        // Initially revealed, child mounted once.
+        #expect(revealer.getRevealChild() == true)
+        #expect(ConditionProbe.firstCount == 1)
+
+        // Toggle to false — child still mounted, just hidden.
+        box.set(false)
+        #expect(revealer.getRevealChild() == false)
+        #expect(ConditionProbe.firstCount == 1)
+
+        // Toggle back to true — still same child.
+        box.set(true)
+        #expect(revealer.getRevealChild() == true)
+        #expect(ConditionProbe.firstCount == 1)
+    }
+
+    @Test func optionalViewHidesWhenConditionFalse() {
+        guard Gtk.initCheck() else { return }
+        ConditionProbe.reset()
+
+        let box = StateBox(false)
+        let binding = Binding(box)
+        let view = OptionalView(binding) { FirstProbeLabel() }
+        let widget = AnyView(view).makeWidget(MountContext())
+        let revealer = widget as! Gtk.Revealer
+
+        // Initially hidden, but child WAS mounted (build-once).
+        #expect(revealer.getRevealChild() == false)
+        #expect(ConditionProbe.firstCount == 1)
+
+        // Toggle to true — child visible, no remount.
+        box.set(true)
+        #expect(revealer.getRevealChild() == true)
+        #expect(ConditionProbe.firstCount == 1)
+    }
+}
+
+// MARK: - Test helpers
+
+@MainActor fileprivate enum ConditionProbe {
+    static var firstCount = 0
+    static var secondCount = 0
+
+    static func reset() {
+        firstCount = 0
+        secondCount = 0
+    }
+}
+
+@MainActor fileprivate struct FirstProbeLabel: View, Mountable {
+    var body: Never { fatalError() }
+    func mount(_ ctx: MountContext) -> Gtk.Widget {
+        ConditionProbe.firstCount += 1
+        return Gtk.Label(str: "first")
+    }
+}
+
+@MainActor fileprivate struct SecondProbeLabel: View, Mountable {
+    var body: Never { fatalError() }
+    func mount(_ ctx: MountContext) -> Gtk.Widget {
+        ConditionProbe.secondCount += 1
+        return Gtk.Label(str: "second")
+    }
+}