Fix handling of public imports in upb `protos` generator

I recently ran into an issue with public imports and the `protos` generator.
The includes of fwd.h files are currently generated based on where the message
or extension is defined, but when public imports are involved, this fwd.h
header might not be in the direct dependencies. When the `#include` points to a
transitive dependency then this can result in a layering violation.

This CL fixes the problem by generating fwd.h includes for all direct
dependencies, and making sure the fwd.h files themselves contain `#include`
lines to export their public dependencies.

PiperOrigin-RevId: 540102455

protos_generator/protoc-gen-upb-protos.cc

@@ -57,8 +57,6 @@ void WriteTypedefForwardingHeader(
     Output& output);
 void WriteHeaderMessageForwardDecls(
     const protobuf::FileDescriptor* file,
-    const std::vector<const protobuf::Descriptor*>& file_messages,
-    const std::vector<const protobuf::FieldDescriptor*>& file_exts,
     Output& output);
 
 class Generator : public protoc::CodeGenerator {
@@ -115,6 +113,13 @@ void WriteForwardingHeader(const protobuf::FileDescriptor* file,
       )cc",
       ToPreproc(file->name()));
   output("\n");
+  for (int i = 0; i < file->public_dependency_count(); ++i) {
+    output("#include \"$0\"\n",
+           ForwardingHeaderFilename(file->public_dependency(i)));
+  }
+  if (file->public_dependency_count() > 0) {
+    output("\n");
+  }
   const std::vector<const protobuf::Descriptor*> this_file_messages =
       SortedMessages(file);
   WriteTypedefForwardingHeader(file, this_file_messages, output);
@@ -162,8 +167,7 @@ void WriteHeader(const protobuf::FileDescriptor* file, Output& output) {
     output("\n");
   }
 
-  WriteHeaderMessageForwardDecls(file, this_file_messages, this_file_exts,
-                                 output);
+  WriteHeaderMessageForwardDecls(file, output);
   WriteStartNamespace(file, output);
 
   std::vector<const protobuf::EnumDescriptor*> this_file_enums =
@@ -258,43 +262,13 @@ void WriteTypedefForwardingHeader(
 /// Writes includes for upb C minitables and fwd.h for transitive typedefs.
 void WriteHeaderMessageForwardDecls(
     const protobuf::FileDescriptor* file,
-    const std::vector<const protobuf::Descriptor*>& file_messages,
-    const std::vector<const protobuf::FieldDescriptor*>& file_exts,
     Output& output) {
   // Import forward-declaration of types defined in this file.
   output("#include \"$0\"\n", UpbCFilename(file));
   output("#include \"$0\"\n", ForwardingHeaderFilename(file));
-  // Forward-declare types not in this file, but used as submessages.
-  // Order by full name for consistent ordering.
-  std::map<std::string, const protobuf::Descriptor*> forward_messages;
-
-  for (auto* message : file_messages) {
-    for (int i = 0; i < message->field_count(); i++) {
-      const protobuf::FieldDescriptor* field = message->field(i);
-      if (field->cpp_type() == protobuf::FieldDescriptor::CPPTYPE_MESSAGE &&
-          field->file() != field->message_type()->file()) {
-        forward_messages[field->message_type()->full_name()] =
-            field->message_type();
-      }
-    }
-  }
-  for (auto* ext : file_exts) {
-    if (ext->file() != ext->containing_type()->file()) {
-      forward_messages[ext->containing_type()->full_name()] =
-          ext->containing_type();
-      if (ext->cpp_type() == protobuf::FieldDescriptor::CPPTYPE_MESSAGE) {
-        forward_messages[ext->message_type()->full_name()] =
-            ext->message_type();
-      }
-    }
-  }
-  std::map<std::string, const protobuf::FileDescriptor*> files_to_import;
-  for (const auto& pair : forward_messages) {
-    files_to_import[ForwardingHeaderFilename(pair.second->file())] = file;
-  }
-  for (const auto& pair : files_to_import) {
-    output("#include \"$0\"\n", UpbCFilename(pair.second));
-    output("#include \"$0\"\n", pair.first);
+  // Import forward-declaration of types in dependencies.
+  for (int i = 0; i < file->dependency_count(); ++i) {
+    output("#include \"$0\"\n", ForwardingHeaderFilename(file->dependency(i)));
   }
   output("\n");
 }