Add a debug-only check for depth_ match, to catch a problem that is difficult

to diagnose otherwise.

PiperOrigin-RevId: 485688363

src/google/protobuf/parse_context.cc

@@ -278,7 +278,9 @@ const char* ParseContext::ParseMessage(MessageLite* msg, const char* ptr) {
   int old;
   ptr = ReadSizeAndPushLimitAndDepth(ptr, &old);
   if (ptr == nullptr) return ptr;
+  auto old_depth = depth_;
   ptr = msg->_InternalParse(ptr, this);
+  if (ptr != nullptr) GOOGLE_DCHECK_EQ(old_depth, depth_);
   depth_++;
   if (!PopLimit(old)) return nullptr;
   return ptr;

src/google/protobuf/parse_context.h

@@ -445,7 +445,9 @@ class PROTOBUF_EXPORT ParseContext : public EpsCopyInputStream {
       MessageLite* msg, const char* ptr, const Table* table) {
     int old;
     ptr = ReadSizeAndPushLimitAndDepthInlined(ptr, &old);
+    auto old_depth = depth_;
     ptr = ptr ? TcParser::ParseLoop(msg, ptr, this, table) : nullptr;
+    if (ptr != nullptr) GOOGLE_DCHECK_EQ(old_depth, depth_);
     depth_++;
     if (!PopLimit(old)) return nullptr;
     return ptr;
@@ -456,7 +458,13 @@ class PROTOBUF_EXPORT ParseContext : public EpsCopyInputStream {
       T* msg, const char* ptr, uint32_t tag) {
     if (--depth_ < 0) return nullptr;
     group_depth_++;
+    auto old_depth = depth_;
+    auto old_group_depth = group_depth_;
     ptr = msg->_InternalParse(ptr, this);
+    if (ptr != nullptr) {
+      GOOGLE_DCHECK_EQ(old_depth, depth_);
+      GOOGLE_DCHECK_EQ(old_group_depth, group_depth_);
+    }
     group_depth_--;
     depth_++;
     if (PROTOBUF_PREDICT_FALSE(!ConsumeEndGroup(tag))) return nullptr;
@@ -468,7 +476,13 @@ class PROTOBUF_EXPORT ParseContext : public EpsCopyInputStream {
       MessageLite* msg, const char* ptr, uint32_t tag, const Table* table) {
     if (--depth_ < 0) return nullptr;
     group_depth_++;
+    auto old_depth = depth_;
+    auto old_group_depth = group_depth_;
     ptr = TcParser::ParseLoop(msg, ptr, this, table);
+    if (ptr != nullptr) {
+      GOOGLE_DCHECK_EQ(old_depth, depth_);
+      GOOGLE_DCHECK_EQ(old_group_depth, group_depth_);
+    }
     group_depth_--;
     depth_++;
     if (PROTOBUF_PREDICT_FALSE(!ConsumeEndGroup(tag))) return nullptr;
@@ -835,7 +849,9 @@ PROTOBUF_NODISCARD const char* ParseContext::ParseMessage(T* msg,
   int old;
   ptr = ReadSizeAndPushLimitAndDepth(ptr, &old);
   if (ptr == nullptr) return ptr;
+  auto old_depth = depth_;
   ptr = msg->_InternalParse(ptr, this);
+  if (ptr != nullptr) GOOGLE_DCHECK_EQ(old_depth, depth_);
   depth_++;
   if (!PopLimit(old)) return nullptr;
   return ptr;