Add a SwiftUI paywall example for every subscription state

.github/workflows/swift.yml

@@ -69,6 +69,12 @@ jobs:
             fi
           done
 
+      - name: Build the example app
+        run: |
+          # Examples/PaywallDemo uses the kit only through its public API, as a client would.
+          # Building it catches a public API change that breaks clients but not the tests.
+          xcodebuild build -project Examples/PaywallDemo/PaywallDemo.xcodeproj -scheme PaywallDemo -destination generic/platform=iOS\ Simulator CODE_SIGNING_ALLOWED=NO
+
       - name: Generate DocC
         run: |
          mkdir -p docs

Examples/PaywallDemo/PaywallDemo.storekit

@@ -0,0 +1,146 @@
+{
+  "identifier" : "8C1D5E07",
+  "nonRenewingSubscriptions" : [
+
+  ],
+  "products" : [
+    {
+      "displayPrice" : "0.99",
+      "familyShareable" : false,
+      "internalID" : "6740000001",
+      "localizations" : [
+        {
+          "description" : "A pouch of 100 coins to spend in the app",
+          "displayName" : "100 Coins",
+          "locale" : "en_US"
+        }
+      ],
+      "productID" : "dev.purchasekit.coins.100",
+      "referenceName" : "100 Coins",
+      "type" : "Consumable"
+    },
+    {
+      "displayPrice" : "79.99",
+      "familyShareable" : true,
+      "internalID" : "6740000002",
+      "localizations" : [
+        {
+          "description" : "Every Premium feature, paid once",
+          "displayName" : "Lifetime Unlock",
+          "locale" : "en_US"
+        }
+      ],
+      "productID" : "dev.purchasekit.lifetime",
+      "referenceName" : "Lifetime Unlock",
+      "type" : "NonConsumable"
+    }
+  ],
+  "settings" : {
+    "_applicationInternalID" : "6740000000",
+    "_askToBuyEnabled" : false,
+    "_billingGracePeriodEnabled" : true,
+    "_billingIssuesEnabled" : false,
+    "_developerTeamID" : "",
+    "_disableDialogs" : false,
+    "_failTransactionsEnabled" : false,
+    "_lastSynchronizedDate" : 0,
+    "_locale" : "en_US",
+    "_renewalBillingIssuesEnabled" : false,
+    "_storefront" : "USA",
+    "_storeKitErrors" : [
+
+    ]
+  },
+  "subscriptionGroups" : [
+    {
+      "id" : "21500001",
+      "localizations" : [
+
+      ],
+      "name" : "Premium",
+      "subscriptions" : [
+        {
+          "adHocOffers" : [
+            {
+              "displayPrice" : "0.99",
+              "internalID" : "6740000111",
+              "numberOfPeriods" : 1,
+              "offerID" : "dev.purchasekit.premium.monthly.retry",
+              "paymentMode" : "payAsYouGo",
+              "referenceName" : "First Month Back",
+              "subscriptionPeriod" : "P1M"
+            }
+          ],
+          "codeOffers" : [
+
+          ],
+          "displayPrice" : "4.99",
+          "familyShareable" : false,
+          "groupNumber" : 2,
+          "internalID" : "6740000011",
+          "localizations" : [
+            {
+              "description" : "Premium, billed every month",
+              "displayName" : "Premium Monthly",
+              "locale" : "en_US"
+            }
+          ],
+          "productID" : "dev.purchasekit.premium.monthly",
+          "recurringSubscriptionPeriod" : "P1M",
+          "referenceName" : "Premium Monthly",
+          "subscriptionGroupID" : "21500001",
+          "type" : "RecurringSubscription",
+          "winbackOffers" : [
+            {
+              "displayPrice" : "1.99",
+              "internalID" : "6740000112",
+              "isEligible" : true,
+              "numberOfPeriods" : 3,
+              "offerID" : "dev.purchasekit.premium.monthly.winback",
+              "paymentMode" : "payAsYouGo",
+              "referenceName" : "Welcome Back",
+              "subscriptionPeriod" : "P1M"
+            }
+          ]
+        },
+        {
+          "adHocOffers" : [
+
+          ],
+          "codeOffers" : [
+
+          ],
+          "displayPrice" : "39.99",
+          "familyShareable" : false,
+          "groupNumber" : 1,
+          "internalID" : "6740000012",
+          "introductoryOffer" : {
+            "internalID" : "6740000121",
+            "numberOfPeriods" : 1,
+            "paymentMode" : "free",
+            "subscriptionPeriod" : "P3D"
+          },
+          "localizations" : [
+            {
+              "description" : "Premium, billed once a year",
+              "displayName" : "Premium Yearly",
+              "locale" : "en_US"
+            }
+          ],
+          "productID" : "dev.purchasekit.premium.yearly",
+          "recurringSubscriptionPeriod" : "P1Y",
+          "referenceName" : "Premium Yearly",
+          "subscriptionGroupID" : "21500001",
+          "type" : "RecurringSubscription",
+          "winbackOffers" : [
+
+          ]
+        }
+      ]
+    }
+  ],
+  "version" : {
+    "major" : 4,
+    "minor" : 0
+  }
+}