Take the listing at selection, not at import

Capturing it where the import starts was too late for the one case that
needed it. The merge dialog waits on the user; a reload landing while it
is open replaces the list and re-bases the credential, and confirming
afterwards captured the new generation and passed every check — reading
a row that no longer exists under whoever now owns the account.

The listing is recorded where the row is chosen and carried to the
import, so what answers the dialog is the list that asked the question.

Yattee/Views/Settings/ImportPlaylistsView.swift

@@ -42,6 +42,9 @@ struct ImportPlaylistsView: View {
     // Merge warning state
     @State private var showMergeWarning = false
     @State private var pendingMergePlaylist: Playlist?
+    /// The listing the pending merge was chosen from. The dialog waits on the
+    /// user, so the list can be replaced before they answer it.
+    @State private var pendingMergeGeneration = 0
     @State private var existingLocalPlaylist: LocalPlaylist?
 
     // MARK: - Accessibility Identifiers
@@ -104,7 +107,10 @@ struct ImportPlaylistsView: View {
             ) {
                 Button(String(localized: "import.playlists.mergeWarning.merge")) {
                     if let playlist = pendingMergePlaylist, let localPlaylist = existingLocalPlaylist {
-                        mergeImportTask = Task { await performImport(playlist, into: localPlaylist) }
+                        let generation = pendingMergeGeneration
+                        mergeImportTask = Task {
+                            await performImport(playlist, into: localPlaylist, generation: generation)
+                        }
                     }
                 }
                 Button(String(localized: "common.cancel"), role: .cancel) {
@@ -333,6 +339,11 @@ struct ImportPlaylistsView: View {
     private func addPlaylist(_ playlist: Playlist) async {
         guard let appEnvironment else { return }
 
+        // The listing this row came from, taken here rather than wherever the
+        // import eventually starts: a merge waits on the user, and by then the
+        // list may have been replaced.
+        let generation = listGeneration
+
         // Checked before anything is created: a playlist made for a login that
         // has already gone would be left behind empty, because the import
         // aborts on its first write.
@@ -346,6 +357,7 @@ struct ImportPlaylistsView: View {
         if let existing = localPlaylists.first(where: { $0.title == playlist.title }) {
             // Show merge warning
             pendingMergePlaylist = playlist
+            pendingMergeGeneration = generation
             existingLocalPlaylist = existing
             importingPlaylistID = playlist.id.playlistID
             showMergeWarning = true
@@ -354,7 +366,7 @@ struct ImportPlaylistsView: View {
 
         // Create new local playlist and import
         let localPlaylist = appEnvironment.dataManager.createPlaylist(title: playlist.title)
-        await performImport(playlist, into: localPlaylist)
+        await performImport(playlist, into: localPlaylist, generation: generation)
 
         // The guard above and the one inside are a suspension apart, so the
         // login can still go in between. Nothing was read, and an empty
@@ -364,7 +376,14 @@ struct ImportPlaylistsView: View {
         }
     }
 
-    private func performImport(_ playlist: Playlist, into localPlaylist: LocalPlaylist) async {
+    /// - Parameter generation: the listing `playlist` was chosen from, taken at
+    ///   selection time. Reading it under a later one would fetch whatever that
+    ///   ID happens to name to whoever replaced the login.
+    private func performImport(
+        _ playlist: Playlist,
+        into localPlaylist: LocalPlaylist,
+        generation: Int
+    ) async {
         guard let appEnvironment else { return }
 
         // The login can go, or be replaced, between choosing this playlist and
@@ -372,12 +391,8 @@ struct ImportPlaylistsView: View {
         // Returning quietly would leave the row importing forever and let a
         // batch carry on; reading it under a replacement would fetch whatever
         // that ID means to somebody else.
-        // The listing this playlist was chosen from can be replaced while the
-        // import runs, which re-baselines the credential it is checked
-        // against. Captured so a reload cannot quietly re-authorise it.
-        let generation = listGeneration
-
-        guard let credential = appEnvironment.credential(forInstance: instance),
+        guard generation == listGeneration,
+              let credential = appEnvironment.credential(forInstance: instance),
               credential == loadedCredential else {
             loginChangedDuringImport = true
             importingPlaylistID = nil