Name the no-tag sentinel and use it for the hardcoded -1 tags (#58531)

Summary:
React tags are positive; `-1` marks the absence of one in several places with a bare literal. This names the convention — `kNoTag` in `ReactPrimitives.h`, next to the `Tag` alias and mirroring `ViewUtil.NO_SURFACE_ID` on the Android side — and replaces the literals across the renderer: `ShadowViewMutation`'s `parentTag` default, factories and comparison, the stub view tree (folding its duplicate `NO_VIEW_TAG` constant into `kNoTag`), the `CppMountItem` mirrors on Android, `UIManagerViewTransitionDelegate`'s `nativeTag` and the view transition fallback that feeds it, and the pointer-events no-override comparisons.

Split out of the safe area insets stack: #58530 threads a `Tag` with no-tag semantics through `experimental_flushSync` and wants the named sentinel, but the cleanup stands on its own and can land regardless of that PR's fate.

## Changelog:

[INTERNAL] - Name the no-tag sentinel (`kNoTag`) and use it for the hardcoded `-1` tags

Pull Request resolved: #58531

Test Plan: Compiles via the Fantom tester build; `yarn fantom` mounting-heavy suite passes 224/224 (exercises the `StubViewTree` asserts). C++ API snapshots regenerated — the only delta is the new `kNoTag` constant.

Reviewed By: javache

Differential Revision: D120199347

Pulled By: Abbondanzo

fbshipit-source-id: 4198a33fa601edff53c54bce935814b3414c5820

Author: janicduplessis

packages/react-native/ReactAndroid/src/main/jni/react/fabric/MountItem.cpp

@@ -79,7 +79,7 @@ CppMountItem CppMountItem::UpdateEventEmitterMountItem(
     const ShadowView& shadowView) {
   return {
       .type = CppMountItem::Type::UpdateEventEmitter,
-      .parentTag = -1,
+      .parentTag = kNoTag,
       .oldChildShadowView = {},
       .newChildShadowView = shadowView,
       .index = -1};
@@ -88,7 +88,7 @@ CppMountItem CppMountItem::UpdatePaddingMountItem(
     const ShadowView& shadowView) {
   return {
       .type = CppMountItem::Type::UpdatePadding,
-      .parentTag = -1,
+      .parentTag = kNoTag,
       .oldChildShadowView = {},
       .newChildShadowView = shadowView,
       .index = -1};
@@ -97,7 +97,7 @@ CppMountItem CppMountItem::UpdateOverflowInsetMountItem(
     const ShadowView& shadowView) {
   return {
       .type = CppMountItem::Type::UpdateOverflowInset,
-      .parentTag = -1,
+      .parentTag = kNoTag,
       .oldChildShadowView = {},
       .newChildShadowView = shadowView,
       .index = -1};

packages/react-native/ReactAndroid/src/main/jni/react/fabric/MountItem.h

@@ -59,7 +59,7 @@ struct CppMountItem final {
 #pragma mark - Fields
 
   Type type = {Create};
-  Tag parentTag = -1;
+  Tag parentTag = kNoTag;
   ShadowView oldChildShadowView = {};
   ShadowView newChildShadowView = {};
   int index = {};

packages/react-native/ReactCommon/react/renderer/core/ReactPrimitives.h

@@ -18,6 +18,11 @@ namespace facebook::react {
  */
 using Tag = int32_t;
 
+/*
+ * Value representing an unset tag.
+ */
+constexpr Tag kNoTag = -1;
+
 /*
  * An id of a running Surface instance that is used to refer to the instance.
  */

packages/react-native/ReactCommon/react/renderer/mounting/ShadowViewMutation.cpp

@@ -14,7 +14,7 @@ namespace facebook::react {
 ShadowViewMutation ShadowViewMutation::CreateMutation(ShadowView shadowView) {
   return {
       /* .type = */ Create,
-      /* .parentTag = */ -1,
+      /* .parentTag = */ kNoTag,
       /* .oldChildShadowView = */ {},
       /* .newChildShadowView = */ std::move(shadowView),
       /* .index = */ -1,
@@ -24,7 +24,7 @@ ShadowViewMutation ShadowViewMutation::CreateMutation(ShadowView shadowView) {
 ShadowViewMutation ShadowViewMutation::DeleteMutation(ShadowView shadowView) {
   return {
       /* .type = */ Delete,
-      /* .parentTag = */ -1,
+      /* .parentTag = */ kNoTag,
       /* .oldChildShadowView = */ std::move(shadowView),
       /* .newChildShadowView = */ {},
       /* .index = */ -1,
@@ -131,7 +131,7 @@ std::vector<DebugStringConvertibleObject> getDebugProps(
                                              mutation.newChildShadowView,
                                              options)}
           : DebugStringConvertibleObject{},
-      mutation.parentTag != -1
+      mutation.parentTag != kNoTag
           ? DebugStringConvertibleObject{"parent",
                                          getDebugDescription(
                                              mutation.parentTag,

packages/react-native/ReactCommon/react/renderer/mounting/ShadowViewMutation.h

@@ -94,7 +94,7 @@ struct ShadowViewMutation final {
 #pragma mark - Fields
 
   Type type = {Create};
-  Tag parentTag = -1;
+  Tag parentTag = kNoTag;
   ShadowView oldChildShadowView = {};
   ShadowView newChildShadowView = {};
   int index = -1;

packages/react-native/ReactCommon/react/renderer/mounting/stubs/StubView.h

@@ -19,8 +19,6 @@
 
 namespace facebook::react {
 
-static const int NO_VIEW_TAG = -1;
-
 class StubView final {
  public:
   using Shared = std::shared_ptr<StubView>;
@@ -42,7 +40,7 @@ class StubView final {
   LayoutMetrics layoutMetrics;
   State::Shared state;
   std::vector<StubView::Shared> children;
-  Tag parentTag{NO_VIEW_TAG};
+  Tag parentTag{kNoTag};
 };
 
 bool operator==(const StubView &lhs, const StubView &rhs);

packages/react-native/ReactCommon/react/renderer/mounting/stubs/StubViewTree.cpp

@@ -51,7 +51,7 @@ void StubViewTree::mutate(const ShadowViewMutationList& mutations) {
   for (const auto& mutation : mutations) {
     switch (mutation.type) {
       case ShadowViewMutation::Create: {
-        react_native_assert(mutation.parentTag == -1);
+        react_native_assert(mutation.parentTag == kNoTag);
         react_native_assert(mutation.oldChildShadowView == ShadowView{});
         react_native_assert(mutation.newChildShadowView.props);
         auto stubView = std::make_shared<StubView>();
@@ -81,7 +81,7 @@ void StubViewTree::mutate(const ShadowViewMutationList& mutations) {
                      << "] ##"
                      << std::hash<ShadowView>{}(mutation.oldChildShadowView);
         });
-        react_native_assert(mutation.parentTag == -1);
+        react_native_assert(mutation.parentTag == kNoTag);
         react_native_assert(mutation.newChildShadowView == ShadowView{});
         auto tag = mutation.oldChildShadowView.tag;
         react_native_assert(hasTag(tag));
@@ -118,7 +118,7 @@ void StubViewTree::mutate(const ShadowViewMutationList& mutations) {
                        << parentTag << "] @" << mutation.index << "("
                        << parentStubView->children.size() << " children)";
           });
-          react_native_assert(childStubView->parentTag == NO_VIEW_TAG);
+          react_native_assert(childStubView->parentTag == kNoTag);
           react_native_assert(
               mutation.index >= 0 &&
               parentStubView->children.size() >=
@@ -182,7 +182,7 @@ void StubViewTree::mutate(const ShadowViewMutationList& mutations) {
                   static_cast<size_t>(mutation.index) &&
               parentStubView->children[mutation.index]->tag ==
                   childStubView->tag);
-          childStubView->parentTag = NO_VIEW_TAG;
+          childStubView->parentTag = kNoTag;
           parentStubView->children.erase(
               parentStubView->children.begin() + mutation.index);
         }

packages/react-native/ReactCommon/react/renderer/uimanager/PointerEventsProcessor.cpp

@@ -389,8 +389,9 @@ void PointerEventsProcessor::processPendingPointerCapture(
   }
 
   auto pendingOverrideTag =
-      (hasPendingOverride) ? pendingOverride->getTag() : -1;
-  auto activeOverrideTag = (hasActiveOverride) ? activeOverride->getTag() : -1;
+      (hasPendingOverride) ? pendingOverride->getTag() : kNoTag;
+  auto activeOverrideTag =
+      (hasActiveOverride) ? activeOverride->getTag() : kNoTag;
 
   if (hasActiveOverride && activeOverrideTag != pendingOverrideTag) {
     auto retargeted = retargetPointerEvent(event, *activeOverride, uiManager);

packages/react-native/ReactCommon/react/renderer/uimanager/UIManagerViewTransitionDelegate.h

@@ -52,7 +52,7 @@ class UIManagerViewTransitionDelegate {
     Float y{0};
     Float width{0};
     Float height{0};
-    Tag nativeTag{-1};
+    Tag nativeTag{kNoTag};
   };
 
   virtual std::optional<ViewTransitionInstance> getViewTransitionInstance(

packages/react-native/ReactCommon/react/renderer/viewtransition/ViewTransitionModule.cpp

@@ -554,7 +554,7 @@ ViewTransitionModule::getViewTransitionInstance(
       auto pseudoElementIt = oldPseudoElementNodes_.find(name);
       auto nativeTag = pseudoElementIt != oldPseudoElementNodes_.end()
           ? pseudoElementIt->second->getTag()
-          : -1;
+          : kNoTag;
       return ViewTransitionInstance{
           .x = view.layoutMetrics.originFromRoot.x,
           .y = view.layoutMetrics.originFromRoot.y,