Showing Badge for Blank Card Fronts in Previewer

AnkiDroid/src/main/java/com/ichi2/anki/previewer/TemplatePreviewerPage.kt

@@ -55,8 +55,14 @@ class TemplatePreviewerPage : Fragment(R.layout.template_previewer_container) {
         val tabLayout = view.findViewById<TabLayout>(R.id.tab_layout)
 
         lifecycleScope.launch {
-            for (templateName in viewModel.getTemplateNames()) {
-                tabLayout.addTab(tabLayout.newTab().setText(templateName))
+            val cardsWithEmptyFronts = viewModel.cardsWithEmptyFronts?.await()
+            for ((index, templateName) in viewModel.getTemplateNames().withIndex()) {
+                val newTab = tabLayout.newTab().setText(templateName)
+                if (cardsWithEmptyFronts?.get(index) == true) {
+                    val badge = newTab.getOrCreateBadge()
+                    badge.horizontalOffset = -4
+                }
+                tabLayout.addTab(newTab)
             }
             tabLayout.selectTab(tabLayout.getTabAt(viewModel.getCurrentTabIndex()))
             tabLayout.addOnTabSelectedListener(

AnkiDroid/src/main/java/com/ichi2/anki/previewer/TemplatePreviewerViewModel.kt

@@ -39,6 +39,7 @@ import kotlinx.coroutines.Deferred
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.collectLatest
 import kotlinx.parcelize.Parcelize
+import org.intellij.lang.annotations.Language
 import org.jetbrains.annotations.VisibleForTesting
 
 class TemplatePreviewerViewModel(
@@ -63,6 +64,11 @@ class TemplatePreviewerViewModel(
     override var currentCard: Deferred<Card>
     override val server = AnkiServer(this).also { it.start() }
 
+    /**
+     * Ordered list of cards with empty fronts
+     */
+    internal val cardsWithEmptyFronts: Deferred<List<Boolean>>?
+
     init {
         note =
             asyncIO {
@@ -105,9 +111,28 @@ class TemplatePreviewerViewModel(
                     val tr = CollectionManager.TR
                     clozeNumbers.await().map { tr.cardTemplatesCard(it) }
                 }
+            cardsWithEmptyFronts = null
         } else {
             clozeOrds = null
             templateNames = CompletableDeferred(notetype.templatesNames)
+            cardsWithEmptyFronts =
+                asyncIO {
+                    val note = note.await()
+                    List(templateNames.await().size) { ord ->
+                        val questionText =
+                            withCol {
+                                note
+                                    .ephemeralCard(
+                                        col = this,
+                                        ord = ord,
+                                        customNoteType = notetype,
+                                        fillEmpty = fillEmpty,
+                                        deckId = arguments.deckId,
+                                    ).renderOutput(this)
+                            }.questionText
+                        EMPTY_FRONT_LINK in questionText
+                    }
+                }
         }
     }
 
@@ -205,6 +230,9 @@ class TemplatePreviewerViewModel(
         }
 
     companion object {
+        @Language("HTML")
+        private const val EMPTY_FRONT_LINK = """<a href='https://docs.ankiweb.net/templates/errors.html#front-of-card-is-blank'>"""
+
         fun factory(
             arguments: TemplatePreviewerArguments,
             cardMediaPlayer: CardMediaPlayer,

AnkiDroid/src/test/java/com/ichi2/anki/previewer/TemplatePreviewerViewModelTest.kt

@@ -57,6 +57,21 @@ class TemplatePreviewerViewModelTest : JvmTest() {
         }
     }
 
+    @Test
+    fun `empty front field detected correctly for tab badge`() =
+        runOptionalReversedTest(
+            fields =
+                mutableListOf(
+                    "we have two normal fields",
+                    "and purposefully leave the third blank",
+                    "",
+                ),
+        ) {
+            onPageFinished(false)
+            assertThat(this.cardsWithEmptyFronts!!.await()[0], equalTo(false))
+            assertThat(this.cardsWithEmptyFronts!!.await()[1], equalTo(true))
+        }
+
     private fun runClozeTest(
         ord: Int = 0,
         fields: MutableList<String>? = null,
@@ -73,4 +88,21 @@ class TemplatePreviewerViewModelTest : JvmTest() {
         val viewModel = TemplatePreviewerViewModel(arguments, mock())
         block(viewModel)
     }
+
+    private fun runOptionalReversedTest(
+        ord: Int = 0,
+        fields: MutableList<String>? = null,
+        block: suspend TemplatePreviewerViewModel.() -> Unit,
+    ) = runTest {
+        val notetype = col.notetypes.byName("Basic (optional reversed card)")!!
+        val arguments =
+            TemplatePreviewerArguments(
+                notetypeFile = NotetypeFile(tempDirectory.root, notetype),
+                fields = fields ?: mutableListOf("question text", "answer text", "y"),
+                tags = mutableListOf(),
+                ord = ord,
+            )
+        val viewModel = TemplatePreviewerViewModel(arguments, mock())
+        block(viewModel)
+    }
 }