fix: refresh NoteEditor fields after restoring templates to default

AnkiDroid/src/main/java/com/ichi2/anki/NoteEditorFragment.kt

@@ -341,6 +341,7 @@ class NoteEditorFragment :
             NoteEditorActivityResultCallback {
                 // Note type can change regardless of exit type - update ourselves and CardBrowser
                 reloadRequired = true
+                val previousFieldNames = editorNote!!.notetype.fieldsNames.toList()
                 editorNote!!.notetype = getColUnsafe.notetypes.get(editorNote!!.noteTypeId)!!
                 if (currentEditedCard == null ||
                     !editorNote!!
@@ -355,6 +356,7 @@ class NoteEditorFragment :
                         Timber.d("onActivityResult() template edit return - current card is gone, close note editor")
                         showSnackbar(getString(R.string.template_for_current_card_deleted))
                         closeNoteEditor()
+                        return@NoteEditorActivityResultCallback
                     } else {
                         Timber.d("onActivityResult() template edit return, in add mode, just re-display")
                         updateCards(editorNote!!.notetype)
@@ -369,6 +371,7 @@ class NoteEditorFragment :
                     editorNote = currentEditedCard!!.note // update the NoteEditor's working note reference
                     updateCards(editorNote!!.notetype)
                 }
+                repopulateFieldsIfChanged(previousFieldNames)
             },
         )
 
@@ -2893,6 +2896,20 @@ class NoteEditorFragment :
         }
     }
 
+    @VisibleForTesting
+    fun repopulateFieldsIfChanged(previousFieldNames: List<String>) {
+        val newFieldNames = editorNote!!.notetype.fieldsNames.toList()
+        if (newFieldNames != previousFieldNames) {
+            Timber.d(
+                "Note type fields changed from %s to %s, repopulating edit fields",
+                previousFieldNames,
+                newFieldNames,
+            )
+            populateEditFields(FieldChangeType.changeFieldCount(shouldReplaceNewlines()))
+        }
+        updateToolbar()
+    }
+
     companion object {
         // DA 2020-04-13 - Refactoring Plans once tested:
         // * There is a difference in functionality depending on whether we are editing

AnkiDroid/src/test/java/com/ichi2/anki/NoteEditorTest.kt

@@ -663,6 +663,69 @@ class NoteEditorTest : RobolectricTest() {
             assertFalse(hasUnsavedChanges())
         }
 
+    @Test
+    fun `restoring notetype to stock updates field count in editor`() =
+        runTest {
+            val notetype = col.notetypes.byName("Basic")!!
+            col.notetypes.addFieldModChanged(notetype, col.notetypes.newField("Extra"))
+            col.notetypes.update(notetype)
+            col.notetypes.clearCache()
+
+            val note = col.newNote(col.notetypes.get(notetype.id)!!)
+            note.setField(0, "Front")
+            note.setField(1, "Back")
+            note.setField(2, "Extra")
+            col.addNote(note, col.decks.id("Default"))
+
+            val editor = getNoteEditorEditingExistingBasicNote(note, REVIEWER)
+            advanceRobolectricLooper()
+            assertThat(editor.editFields!!.size, equalTo(3))
+
+            // simulate restoreNotetypeToStock: backend drops back to 2 fields
+            val restored = col.notetypes.get(notetype.id)!!
+            col.notetypes.removeField(restored, restored.fields.last())
+            col.notetypes.update(restored)
+            col.notetypes.clearCache()
+
+            val previousFieldNames =
+                editor.editorNote!!
+                    .notetype.fieldsNames
+                    .toList()
+            editor.editorNote!!.notetype = col.notetypes.get(notetype.id)!!
+            editor.repopulateFieldsIfChanged(previousFieldNames)
+            advanceRobolectricLooper()
+
+            assertThat(
+                "Field count should match restored notetype",
+                editor.editFields!!.size,
+                equalTo(2),
+            )
+        }
+
+    @Test
+    fun `returning from template editor without field changes does not repopulate fields`() =
+        runTest {
+            val note = addBasicNote("Front", "Back")
+            val editor = getNoteEditorEditingExistingBasicNote(note, REVIEWER)
+            advanceRobolectricLooper()
+
+            val originalRef = editor.editFields
+            val previousFieldNames =
+                editor.editorNote!!
+                    .notetype.fieldsNames
+                    .toList()
+
+            editor.repopulateFieldsIfChanged(previousFieldNames)
+            advanceRobolectricLooper()
+
+            assertThat(editor.editFields!!.size, equalTo(2))
+            assertThat(
+                "editFields reference must not change when fields are unchanged",
+                editor.editFields,
+                equalTo(originalRef),
+            )
+        }
+
     private suspend fun withNoteEditorAdding(
         from: FromScreen = FromScreen.DECK_LIST,
         block: suspend NoteEditorFragment.() -> Unit,