hpb/multi: properly split up internal.h based on backend

hpb/BUILD

@@ -187,14 +187,19 @@ cc_library(
         ":arena",
         ":multibackend",
         ":ptr",
-        "//hpb/backend/upb:extension",
-        "//hpb/backend/upb:interop",
         "//hpb/internal:message_lock",
         "//hpb/internal:template_help",
         "//upb/message",
         "//upb/mini_table",
         "@abseil-cpp//absl/base:core_headers",
-    ],
+    ] + select({
+        "//hpb:hpb_backend_cpp": [
+        ],
+        "//hpb:hpb_backend_upb": [
+            "//hpb/backend/upb:extension",
+            "//hpb/backend/upb:interop",
+        ],
+    }),
 )
 
 cc_library(

hpb/backend/BUILD

@@ -18,10 +18,12 @@ cc_library(
     ] + select({
         "//hpb:hpb_backend_cpp": [
             "//hpb/backend/cpp:error",
+            "//hpb/backend/cpp:internal",
             "//src/google/protobuf:arena",
         ],
         "//hpb:hpb_backend_upb": [
             "//hpb/backend/upb:error",
+            "//hpb/backend/upb:internal",
             "//upb/mem",
         ],
     }),

hpb/backend/cpp/BUILD

@@ -44,6 +44,12 @@ cc_library(
     visibility = ["//hpb:__subpackages__"],
 )
 
+cc_library(
+    name = "internal",
+    hdrs = ["internal.h"],
+    visibility = ["//hpb:__subpackages__"],
+)
+
 cc_test(
     name = "cpp_test",
     srcs = ["cpp_test.cc"],

hpb/backend/cpp/internal.h

@@ -0,0 +1,15 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2025 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#ifndef GOOGLE_PROTOBUF_HPB_BACKEND_CPP_INTERNAL_H__
+#define GOOGLE_PROTOBUF_HPB_BACKEND_CPP_INTERNAL_H__
+
+namespace hpb::internal {
+struct PrivateAccess {};
+}  // namespace hpb::internal
+
+#endif  // GOOGLE_PROTOBUF_HPB_BACKEND_CPP_INTERNAL_H__

hpb/backend/types.h

@@ -11,10 +11,12 @@
 #include "hpb/multibackend.h"
 #if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 #include "hpb/backend/upb/error.h"
+#include "hpb/backend/upb/internal.h"
 #include "upb/mem/arena.hpp"
 #elif HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_CPP
 #include "google/protobuf/arena.h"
 #include "hpb/backend/cpp/error.h"
+#include "hpb/backend/cpp/internal.h"
 #endif
 
 namespace hpb {

hpb/backend/upb/BUILD

@@ -43,6 +43,7 @@ cc_library(
     ],
     deps = [
         "//hpb:ptr",
+        "//hpb/backend:types",
         "//hpb/internal",
         "//upb/base",
         "//upb/mem",
@@ -53,6 +54,16 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "internal",
+    hdrs = ["internal.h"],
+    visibility = ["//hpb:__subpackages__"],
+    deps = [
+        "//upb/mem",
+        "//upb/message",
+    ],
+)
+
 cc_test(
     name = "interop_test",
     srcs = ["interop_test.cc"],

hpb/backend/upb/internal.h

@@ -0,0 +1,65 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2025 Google LLC.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#ifndef GOOGLE_PROTOBUF_HPB_BACKEND_UPB_INTERNAL_H__
+#define GOOGLE_PROTOBUF_HPB_BACKEND_UPB_INTERNAL_H__
+
+#include <cstdint>
+#include <utility>
+#include "upb/mem/arena.h"
+#include "upb/message/message.h"
+
+namespace hpb::internal {
+
+struct PrivateAccess {
+  template <typename T>
+  static auto* GetInternalMsg(T&& message) {
+    return message->msg();
+  }
+  template <typename T>
+  static auto* GetInternalArena(T&& message) {
+    return message->arena();
+  }
+  template <typename T>
+  static auto* GetInternalUPBArena(T&& arena) {
+    return arena.arena_.ptr();
+  }
+  template <typename T>
+  static auto Proxy(upb_Message* p, upb_Arena* arena) {
+    return typename T::Proxy(p, arena);
+  }
+  template <typename T>
+  static auto CProxy(const upb_Message* p, upb_Arena* arena) {
+    return typename T::CProxy(p, arena);
+  }
+  template <typename T>
+  static auto CreateMessage(upb_Arena* arena) {
+    return typename T::Proxy(upb_Message_New(T::minitable(), arena), arena);
+  }
+
+  template <typename T, typename... Args>
+  static constexpr auto InvokeConstructor(Args&&... args) {
+    return T(std::forward<Args>(args)...);
+  }
+
+  template <typename ExtensionId>
+  static constexpr uint32_t GetExtensionNumber(const ExtensionId& id) {
+    return id.number();
+  }
+
+  template <typename ExtensionId>
+  static decltype(auto) GetDefaultValue(const ExtensionId& id) {
+    return id.default_value();
+  }
+};
+
+template <typename T>
+struct AssociatedUpbTypes;
+
+}  // namespace hpb::internal
+
+#endif  // GOOGLE_PROTOBUF_HPB_BACKEND_UPB_INTERNAL_H__

hpb/extension.h

@@ -13,14 +13,17 @@
 
 #include "absl/base/attributes.h"
 #include "hpb/arena.h"
-#include "hpb/backend/upb/extension.h"
-#include "hpb/backend/upb/interop.h"
 #include "hpb/internal/message_lock.h"
 #include "hpb/internal/template_help.h"
 #include "hpb/multibackend.h"
 #include "hpb/ptr.h"
+
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
+#include "hpb/backend/upb/extension.h"
+#include "hpb/backend/upb/interop.h"
 #include "upb/message/accessors.h"
 #include "upb/mini_table/extension_registry.h"
+#endif
 
 namespace hpb {
 // upb has a notion of an ExtensionRegistry. We expect most callers to use
@@ -87,6 +90,7 @@ class ExtensionRegistry {
   explicit ExtensionRegistry() = default;
 };
 
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
 template <typename T, typename Extendee, typename Extension,
           typename = hpb::internal::EnableIfHpbClassThatHasExtensions<T>>
 ABSL_MUST_USE_RESULT bool HasExtension(
@@ -186,6 +190,7 @@ constexpr uint32_t ExtensionNumber(
     const internal::ExtensionIdentifier<T, Extension>& id) {
   return internal::PrivateAccess::GetExtensionNumber(id);
 }
+#endif
 
 }  // namespace hpb
 

hpb/internal/BUILD

@@ -49,9 +49,15 @@ cc_library(
         "//hpb:__subpackages__",
     ],
     deps = [
-        "//upb/mem",
-        "//upb/message",
-    ],
+        "//hpb:multibackend",
+    ] + select({
+        "//hpb:hpb_backend_upb": [
+            "//hpb/backend/upb:internal",
+        ],
+        "//hpb:hpb_backend_cpp": [
+            "//hpb/backend/cpp:internal",
+        ],
+    }),
 )
 
 cc_library(

hpb/internal/internal.h

@@ -8,59 +8,13 @@
 #ifndef GOOGLE_PROTOBUF_HPB_INTERNAL_INTERNAL_H__
 #define GOOGLE_PROTOBUF_HPB_INTERNAL_INTERNAL_H__
 
-#include <cstdint>
-#include <utility>
-
-#include "upb/mem/arena.h"
-#include "upb/message/message.h"
-
-namespace hpb::internal {
-
-struct PrivateAccess {
-  template <typename T>
-  static auto* GetInternalMsg(T&& message) {
-    return message->msg();
-  }
-  template <typename T>
-  static auto* GetInternalArena(T&& message) {
-    return message->arena();
-  }
-  template <typename T>
-  static auto* GetInternalUPBArena(T&& arena) {
-    return arena.arena_.ptr();
-  }
-  template <typename T>
-  static auto Proxy(upb_Message* p, upb_Arena* arena) {
-    return typename T::Proxy(p, arena);
-  }
-  template <typename T>
-  static auto CProxy(const upb_Message* p, upb_Arena* arena) {
-    return typename T::CProxy(p, arena);
-  }
-  template <typename T>
-  static auto CreateMessage(upb_Arena* arena) {
-    return typename T::Proxy(upb_Message_New(T::minitable(), arena), arena);
-  }
-
-  template <typename T, typename... Args>
-  static constexpr auto InvokeConstructor(Args&&... args) {
-    return T(std::forward<Args>(args)...);
-  }
-
-  template <typename ExtensionId>
-  static constexpr uint32_t GetExtensionNumber(const ExtensionId& id) {
-    return id.number();
-  }
-
-  template <typename ExtensionId>
-  static decltype(auto) GetDefaultValue(const ExtensionId& id) {
-    return id.default_value();
-  }
-};
-
-template <typename T>
-struct AssociatedUpbTypes;
-
-}  // namespace hpb::internal
+#include "hpb/multibackend.h"
+#if HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_UPB
+#include "hpb/backend/upb/internal.h"
+#elif HPB_INTERNAL_BACKEND == HPB_INTERNAL_BACKEND_CPP
+#include "hpb/backend/cpp/internal.h"
+#else
+#error "Unsupported hpb backend"
+#endif
 
 #endif  // GOOGLE_PROTOBUF_HPB_INTERNAL_INTERNAL_H__