perf(mobile): prepare word diffs for visible rows

apps/mobile/modules/t3-review-diff/android/src/main/java/expo/modules/t3reviewdiff/ReviewDiffCanvasDrawing.kt

@@ -15,6 +15,7 @@ import kotlin.math.min
 internal class ReviewDiffCanvasDrawing(context: Context) {
   private val density = context.resources.displayMetrics.density
   var theme: DiffTheme = DiffTheme.fallback("light")
+  private val wordDiffRangesByRowId = mutableMapOf<String, List<DiffWordDiffRange>>()
 
   val backgroundPaint = Paint()
   val borderPaint = Paint(Paint.ANTI_ALIAS_FLAG)
@@ -41,6 +42,14 @@ internal class ReviewDiffCanvasDrawing(context: Context) {
     uiPaint.typeface = Typeface.DEFAULT_BOLD
   }
 
+  fun mergeWordDiffRangesByRowId(patch: Map<String, List<DiffWordDiffRange>>) {
+    wordDiffRangesByRowId.putAll(patch)
+  }
+
+  fun clearWordDiffRanges() {
+    wordDiffRangesByRowId.clear()
+  }
+
   fun fileHeaderChevronRect(top: Int, bottom: Int, style: DiffStyle): RectF {
     val centerY = (top + bottom) / 2f
     val left = style.fileHeaderHorizontalPaddingPx
@@ -205,14 +214,15 @@ internal class ReviewDiffCanvasDrawing(context: Context) {
     top: Int,
     bottom: Int
   ) {
-    if (row.wordDiffRanges.isEmpty() || (row.change != "add" && row.change != "delete")) return
+    val ranges = wordDiffRangesByRowId[row.id] ?: row.wordDiffRanges
+    if (ranges.isEmpty() || (row.change != "add" && row.change != "delete")) return
     val color = if (row.change == "add") theme.addBar else theme.deleteBar
     backgroundPaint.color = withAlpha(color, 71)
     val characterWidth = textPaint.measureText("M")
     val fontHeight = textPaint.fontMetrics.run { descent - ascent }
     val highlightHeight = max(4f * density, min(bottom - top - 4f * density, fontHeight))
     val highlightTop = (top + bottom - highlightHeight) / 2f
-    row.wordDiffRanges.forEach { range ->
+    ranges.forEach { range ->
       val left = codeX + range.start * characterWidth
       val right = max(left + 2f * density, codeX + range.end * characterWidth)
       canvas.drawRoundRect(

apps/mobile/modules/t3-review-diff/android/src/main/java/expo/modules/t3reviewdiff/T3ReviewDiffView.kt

@@ -61,8 +61,8 @@ class T3ReviewDiffView(context: Context, appContext: AppContext) : ExpoView(cont
       onDebug(
         mapOf(
           "message" to "visible-range",
-          "firstRowIndex" to first,
-          "lastRowIndex" to last,
+          "firstRowIndex" to (visibleRows.getOrNull(first)?.sourceIndex ?: first),
+          "lastRowIndex" to (visibleRows.getOrNull(last)?.sourceIndex ?: last),
         ),
       )
       emitVisibleFile(first)
@@ -78,13 +78,15 @@ class T3ReviewDiffView(context: Context, appContext: AppContext) : ExpoView(cont
     if (tokensResetKey == value) return
     tokensResetKey = value
     canvasView.tokensByRowId = emptyMap()
+    canvasView.drawing.clearWordDiffRanges()
   }
 
   fun setContentResetKey(value: String) {
     if (contentResetKey == value) return
     contentResetKey = value
     tokensDecodeGeneration += 1
     canvasView.tokensByRowId = emptyMap()
+    canvasView.drawing.clearWordDiffRanges()
     lastVisibleFileId = null
     pendingInitialScroll = true
     canvasView.setVerticalOffset(0)
@@ -167,18 +169,27 @@ class T3ReviewDiffView(context: Context, appContext: AppContext) : ExpoView(cont
   }
 
   fun setTokensPatchJson(value: String) {
+    val expectedContentResetKey = contentResetKey
     payloadDecodeExecutor.execute {
       try {
         val payload = JSONObject(value)
         val resetKey = payload.optString("resetKey")
         val decodedTokens = parseTokensObject(
           payload.optJSONObject("tokensByRowId") ?: JSONObject(),
         )
+        val decodedWordDiffRanges = parseWordDiffRangesObject(
+          payload.optJSONObject("wordDiffRangesByRowId") ?: JSONObject(),
+        )
         post {
+          if (expectedContentResetKey != contentResetKey) return@post
           if (resetKey.isNotEmpty() && resetKey != tokensResetKey) return@post
           if (decodedTokens.isNotEmpty()) {
             canvasView.tokensByRowId = canvasView.tokensByRowId + decodedTokens
           }
+          if (decodedWordDiffRanges.isNotEmpty()) {
+            canvasView.drawing.mergeWordDiffRangesByRowId(decodedWordDiffRanges)
+            canvasView.invalidate()
+          }
         }
       } catch (_: Exception) {
       }
@@ -434,6 +445,8 @@ private data class HorizontalPanTarget(
 )
 
 internal data class DiffRow(
+  // JavaScript range requests use the full payload position, even when files are collapsed.
+  val sourceIndex: Int,
   val kind: String,
   val id: String,
   val fileId: String,
@@ -646,7 +659,7 @@ internal data class DiffStyle(
 
 private class DiffCanvasView(context: Context) : View(context) {
   private val density = resources.displayMetrics.density
-  private val drawing = ReviewDiffCanvasDrawing(context)
+  val drawing = ReviewDiffCanvasDrawing(context)
   private val backgroundPaint = drawing.backgroundPaint
   private val borderPaint = drawing.borderPaint
   private val textPaint = drawing.textPaint
@@ -1337,6 +1350,7 @@ private fun parseRows(value: String): List<DiffRow> = try {
   List(array.length()) { index ->
     val row = array.getJSONObject(index)
     DiffRow(
+      sourceIndex = index,
       kind = row.optString("kind"),
       id = row.optString("id"),
       fileId = row.optString("fileId"),
@@ -1371,6 +1385,17 @@ private fun parseWordDiffRanges(value: JSONArray): List<DiffWordDiffRange> = bui
   }
 }
 
+private fun parseWordDiffRangesObject(
+  value: JSONObject
+): Map<String, List<DiffWordDiffRange>> = buildMap {
+  val keys = value.keys()
+  while (keys.hasNext()) {
+    val rowId = keys.next()
+    val ranges = value.optJSONArray(rowId) ?: continue
+    put(rowId, parseWordDiffRanges(ranges))
+  }
+}
+
 private fun parseTokensObject(value: String): Map<String, List<DiffToken>> = try {
   parseTokensObject(JSONObject(value))
 } catch (_: Exception) {

apps/mobile/modules/t3-review-diff/ios/T3ReviewDiffView.swift

@@ -36,6 +36,7 @@ private struct ReviewDiffNativeTokenPatch: Decodable, Sendable {
   let resetKey: String?
   let chunkIndex: Int?
   let tokensByRowId: [String: [ReviewDiffNativeToken]]?
+  let wordDiffRangesByRowId: [String: [ReviewDiffNativeWordDiffRange]]?
 }
 
 private struct ReviewDiffNativeThemePayload: Decodable {
@@ -520,11 +521,17 @@ public final class T3ReviewDiffView: ExpoView, UIScrollViewDelegate {
           }
 
           let tokensByRowId = patch.tokensByRowId ?? [:]
-          if tokensByRowId.isEmpty {
+          let wordDiffRangesByRowId = patch.wordDiffRangesByRowId ?? [:]
+          if tokensByRowId.isEmpty && wordDiffRangesByRowId.isEmpty {
             return
           }
 
-          self.contentView.mergeTokensByRowId(tokensByRowId)
+          if !tokensByRowId.isEmpty {
+            self.contentView.mergeTokensByRowId(tokensByRowId)
+          }
+          if !wordDiffRangesByRowId.isEmpty {
+            self.contentView.mergeWordDiffRangesByRowId(wordDiffRangesByRowId)
+          }
           if let chunkIndex = patch.chunkIndex, chunkIndex < 5 || chunkIndex.isMultiple(of: 10) {
             self.emitDebug("tokens-patch-decoded", [
               "chunkIndex": chunkIndex,
@@ -549,6 +556,7 @@ public final class T3ReviewDiffView: ExpoView, UIScrollViewDelegate {
 
     self.tokensResetKey = tokensResetKey
     contentView.tokensByRowId = [:]
+    contentView.clearWordDiffRanges()
     emitDebug("tokens-reset", [
       "resetKey": tokensResetKey,
     ])
@@ -563,6 +571,7 @@ public final class T3ReviewDiffView: ExpoView, UIScrollViewDelegate {
     rowsDecodeGeneration += 1
     tokensDecodeGeneration += 1
     contentView.tokensByRowId = [:]
+    contentView.clearWordDiffRanges()
     rows = []
     contentView.rows = []
     hasAppliedInitialRowIndex = false
@@ -951,6 +960,18 @@ private final class ReviewDiffContentView: UIView, UIGestureRecognizerDelegate {
     setNeedsDisplayForVisibleBounds()
   }
 
+  private var wordDiffRangesByRowId: [String: [ReviewDiffNativeWordDiffRange]] = [:]
+
+  func mergeWordDiffRangesByRowId(_ patch: [String: [ReviewDiffNativeWordDiffRange]]) {
+    wordDiffRangesByRowId.merge(patch) { _, next in next }
+    setNeedsDisplayForVisibleBounds()
+  }
+
+  func clearWordDiffRanges() {
+    wordDiffRangesByRowId.removeAll()
+    setNeedsDisplayForVisibleBounds()
+  }
+
   var collapsedFileIds: Set<String> = [] {
     didSet {
       rebuildRowLayout()
@@ -2268,7 +2289,7 @@ private final class ReviewDiffContentView: UIView, UIGestureRecognizerDelegate {
     context: CGContext,
     horizontalOffset: CGFloat
   ) {
-    guard let ranges = row.wordDiffRanges, !ranges.isEmpty else {
+    guard let ranges = wordDiffRangesByRowId[row.id] ?? row.wordDiffRanges, !ranges.isEmpty else {
       return
     }
 

apps/mobile/package.json

@@ -132,7 +132,9 @@
     "@pierre/trees": "1.0.0-beta.4",
     "@types/react": "~19.2.0",
     "@types/react-dom": "~19.2.3",
+    "@types/react-test-renderer": "19.1.0",
     "babel-preset-expo": "~57.0.9",
+    "react-test-renderer": "19.2.3",
     "tailwindcss": "^4.0.0",
     "typescript": "catalog:"
   },