fix(change-note-types): don't discard undo queue

AnkiDroid/src/main/java/com/ichi2/anki/dialogs/ChangeNoteTypeDialog.kt

@@ -68,7 +68,7 @@ import com.ichi2.anki.libanki.NoteTypeId
 import com.ichi2.anki.requireAnkiActivity
 import com.ichi2.anki.showError
 import com.ichi2.anki.snackbar.showSnackbar
-import com.ichi2.anki.sync.launchCatchingRequiringOneWaySyncDiscardUndo
+import com.ichi2.anki.sync.launchCatchingRequiringOneWaySync
 import com.ichi2.anki.ui.BasicItemSelectedListener
 import com.ichi2.anki.ui.internationalization.toSentenceCase
 import com.ichi2.anki.utils.InitStatus
@@ -637,7 +637,7 @@ class ChangeNoteTypeDialog : AnalyticsDialogFragment() {
  * Changes note type of multiple notes, displaying a message on success
  */
 private fun AnkiActivity.changeNoteType(viewModel: ChangeNoteTypeViewModel) =
-    this.launchCatchingRequiringOneWaySyncDiscardUndo {
+    this.launchCatchingRequiringOneWaySync {
         try {
             val notesUpdated =
                 withProgress {

AnkiDroid/src/main/java/com/ichi2/anki/dialogs/ChangeNoteTypeViewModel.kt

@@ -316,8 +316,6 @@ class ChangeNoteTypeViewModel(
             Timber.d("Field map: %s", fieldChangeMap)
             Timber.d("Card map: %s", templateChangeMap)
 
-            withCol { modSchema(check = true) }
-
             val changes =
                 changeNoteTypeOfNotes(
                     noteIds = noteIds,

AnkiDroid/src/main/java/com/ichi2/anki/sync/SchemaChanges.kt

@@ -23,6 +23,7 @@ import com.ichi2.anki.CollectionManager.withCol
 import com.ichi2.anki.R
 import com.ichi2.anki.dialogs.ConfirmationDialog
 import com.ichi2.anki.launchCatchingTask
+import com.ichi2.anki.libanki.Collection
 import com.ichi2.anki.libanki.exception.ConfirmModSchemaException
 import com.ichi2.anki.utils.ext.showDialogFragment
 import com.ichi2.utils.message
@@ -32,6 +33,32 @@ import com.ichi2.utils.show
 import kotlin.coroutines.resume
 import kotlin.coroutines.suspendCoroutine
 
+/**
+ * [launchCatchingTask], showing a one-way sync dialog: [R.string.full_sync_confirmation]
+ *
+ * @param block calls a backend method which unconditionally performs a schema change,
+ *  such as [Collection.changeNotetypeRaw]
+ */
+fun AnkiActivity.launchCatchingRequiringOneWaySync(block: suspend () -> Unit) =
+    launchCatchingTask {
+        if (withCol { !schemaChanged() }) {
+            // .also is used to ensure the activity is used as context
+            val confirmModSchemaDialog =
+                ConfirmationDialog().also { dialog ->
+                    dialog.setArgs(message = getString(R.string.full_sync_confirmation))
+                    dialog.setConfirm {
+                        launchCatchingTask {
+                            block()
+                        }
+                    }
+                }
+            showDialogFragment(confirmModSchemaDialog)
+            return@launchCatchingTask
+        }
+        // TODO: use context(SchemaChangedConfirmed) after bug #20247 is fixed (upstream-issue)
+        block()
+    }
+
 /**
  * [launchCatchingTask], showing a one-way sync dialog: [R.string.full_sync_confirmation]
  *

libanki/src/main/java/com/ichi2/anki/libanki/Notetypes.kt

@@ -561,10 +561,12 @@ class Notetypes(
      *
      * Each value represents the index in the previous notetype.
      * -1 indicates the original value will be discarded.
+     *
+     * **This method updates the schema without confirmation**
      */
     @LibAnkiAlias("change_notetype_of_notes")
     fun changeNotetypeOfNotes(input: ChangeNotetypeRequest): OpChanges {
-        val opBytes = this.col.backend.changeNotetypeRaw(input.toByteArray())
+        val opBytes = col.backend.changeNotetypeRaw(input.toByteArray())
         return OpChanges.parseFrom(opBytes)
     }