android notif [nfc]: Inline createViewPendingIntent; add TODO

This puts it in the context of the notification where it's used.

And in fact that makes it easier for the linter to see what we're
doing, too, and it starts giving a useful new warning!  Suppress it,
with an explanatory comment.  (We'll also note this on zulip#5101.)

android/app/src/main/java/com/zulipmobile/notifications/FCMPushNotifications.kt

@@ -2,6 +2,7 @@
 
 package com.zulipmobile.notifications
 
+import android.annotation.SuppressLint
 import android.app.Notification
 import android.app.NotificationChannel
 import android.app.NotificationManager
@@ -173,20 +174,6 @@ private fun removeNotification(context: Context, fcmMessage: RemoveFcmMessage) {
     }
 }
 
-/** A PendingIntent for opening this message's conversation in the app. */
-private fun createViewPendingIntent(fcmMessage: MessageFcmMessage, context: Context): PendingIntent {
-    // We don't use a URL for this intent; rather we get the information
-    // from the "extra" we add to it.  But, empirically, if the URL is the
-    // same from one notification to the next, then opening the second one
-    // just takes us back to where the first one led, ignoring its different extras.
-    // So we make sure the URL is different every time.
-    val messageKey = "${extractGroupKey(fcmMessage.identity)}|${fcmMessage.zulipMessageId}"
-    val uri = Uri.fromParts("zulip", messageKey, "")
-    val viewIntent = Intent(Intent.ACTION_VIEW, uri, context, NotificationIntentService::class.java)
-    viewIntent.putExtra(EXTRA_NOTIFICATION_DATA, fcmMessage.dataForOpen())
-    return PendingIntent.getService(context, 0, viewIntent, 0)
-}
-
 /**
  * Get the active notification with this tag, if any.
  *
@@ -233,6 +220,12 @@ private fun extractConversationKey(fcmMessage: MessageFcmMessage): String {
     return "$groupKey|$conversation"
 }
 
+/** A unique tag for this Zulip message. */
+private fun extractMessageKey(fcmMessage: MessageFcmMessage): String {
+    val messageKey = "${extractGroupKey(fcmMessage.identity)}|${fcmMessage.zulipMessageId}"
+    return messageKey
+}
+
 /** Handle a MessageFcmMessage, adding or extending notifications in the UI. */
 private fun updateNotification(
     context: Context, fcmMessage: MessageFcmMessage) {
@@ -287,6 +280,8 @@ private fun updateNotification(
         .build()
     messagingStyle.addMessage(fcmMessage.content, fcmMessage.timeMs, sender)
 
+    // See comment at `setContentIntent` below.
+    @SuppressLint("LaunchActivityFromNotification")
     val notification = NotificationCompat.Builder(context, CHANNEL_ID).apply {
         setGroup(groupKey)
 
@@ -308,7 +303,27 @@ private fun updateNotification(
             putInt("lastZulipMessageId", fcmMessage.zulipMessageId)
         }
 
-        setContentIntent(createViewPendingIntent(fcmMessage, context))
+        // The linter warns us here (suppressed by the `SuppressLint` above) that our
+        // current setup where tapping the notification starts NotificationIntentService,
+        // which then goes on to start or interact with our actual Activity, won't be allowed
+        // when targeting Android 12+.  Details:
+        //   https://developer.android.com/about/versions/12/behavior-changes-12#notification-trampolines
+        // TODO(#5101): Replace NotificationIntentService with directly starting an Activity.
+        //   Preferably MainActivity itself, if we can arrange the right behavior regardless
+        //   of whether it's currently in the foreground, the background, or not running.
+        //   Otherwise, a shim analogous to ShareToZulipActivity should work.
+        setContentIntent(
+            PendingIntent.getService(context, 0,
+                Intent(Intent.ACTION_VIEW,
+                    // We don't use a URL for this intent; rather we get the information
+                    // from the "extra" we add to it.  But, empirically, if the URL is the
+                    // same from one notification to the next, then opening the second one
+                    // just takes us back to where the first one led, ignoring its different extras.
+                    // So we make sure the URL is different every time.
+                    Uri.fromParts("zulip", extractMessageKey(fcmMessage), ""),
+                    context, NotificationIntentService::class.java
+                ).putExtra(EXTRA_NOTIFICATION_DATA, fcmMessage.dataForOpen()),
+                0))
         setAutoCancel(true)
     }.build()