Introduce a legacy wrapper around descriptor to begin hiding APIs for editions.

For now, we'll just be hiding syntax getters on FileDescriptor.  Later on this will likely grow to include other APIs that distinguish between proto2/proto3.

PiperOrigin-RevId: 516334230

src/google/protobuf/BUILD.bazel

@@ -480,6 +480,17 @@ cc_library(
     ]),
 )
 
+cc_library(
+    name = "descriptor_legacy",
+    hdrs = ["descriptor_legacy.h"],
+    deps = [
+        ":protobuf_nowkt",
+        ":port_def",
+        "@com_google_absl//absl/strings",
+    ],
+    visibility = ["//:__subpackages__"]
+)
+
 filegroup(
     name = "well_known_type_protos",
     srcs = [

src/google/protobuf/descriptor_legacy.h

@@ -0,0 +1,92 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: kenton@google.com (Kenton Varda)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+//
+// This file contains classes which describe a type of protocol message.
+// You can use a message's descriptor to learn at runtime what fields
+// it contains and what the types of those fields are.  The Message
+// interface also allows you to dynamically access and modify individual
+// fields by passing the FieldDescriptor of the field you are interested
+// in.
+//
+// Most users will not care about descriptors, because they will write
+// code specific to certain protocol types and will simply use the classes
+// generated by the protocol compiler directly.  Advanced users who want
+// to operate on arbitrary types (not known at compile time) may want to
+// read descriptors in order to learn about the contents of a message.
+// A very small number of users will want to construct their own
+// Descriptors, either because they are implementing Message manually or
+// because they are writing something like the protocol compiler.
+//
+// For an example of how you might use descriptors, see the code example
+// at the top of message.h.
+
+#ifndef GOOGLE_PROTOBUF_DESCRIPTOR_LEGACY_H__
+#define GOOGLE_PROTOBUF_DESCRIPTOR_LEGACY_H__
+
+#include "absl/strings/string_view.h"
+#include "google/protobuf/descriptor.h"
+
+// Must be included last.
+#include "google/protobuf/port_def.inc"
+
+// This file is meant to be a temporary housing for legacy descriptor APIs we
+// want to deprecate and remove.  This will help prevent backslide by allowing
+// us to control visibility.
+
+namespace google {
+namespace protobuf {
+
+// Wraps FileDescriptor.
+class PROTOBUF_EXPORT FileDescriptorLegacy {
+ public:
+  explicit FileDescriptorLegacy(const FileDescriptor* desc) : desc_(desc) {}
+
+  // Any dependencies on file-level syntax keyword should be replaced by
+  // feature-level switches to support go/protobuf-editions.
+  using Syntax = FileDescriptor::Syntax;
+  Syntax syntax() const { return desc_->syntax(); }
+  static absl::string_view SyntaxName(Syntax syntax) {
+    return FileDescriptor::SyntaxName(syntax);
+  }
+
+ private:
+  const FileDescriptor* desc_;
+};
+
+}  // namespace protobuf
+}  // namespace google
+
+#include "google/protobuf/port_undef.inc"
+
+#endif  // GOOGLE_PROTOBUF_DESCRIPTOR_LEGACY_H__