Add support for Editions (#297)

As expected, there aren't any (noticeable) issues with enabling editions
in Connect Kotlin. I did take this opportunity to make the
`CodeGenerator` interface match closer to the upstream protobuf
`CodeGenerator` interface (at least from the C++ version) so that
information about editions and features support would be conveyed by the
`CodeGenerator` rather than being hardcoded in the `Plugin` code.

Signed-off-by: John Chadwick <[email protected]>

protoc-gen-connect-kotlin/proto/buf/editions/v1/editions.proto

@@ -0,0 +1,43 @@
+// Copyright 2022-2023 The Connect Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+edition = "2023";
+
+package buf.editions.v1;
+
+option features.field_presence = IMPLICIT;
+
+message EditionsRequest {
+    message NestedMessage {
+        string not_utf8 = 1 [ features.utf8_validation = NONE ];
+    }
+
+    repeated NestedMessage nested = 1 [
+        features.repeated_field_encoding = EXPANDED,
+        features.message_encoding = DELIMITED
+    ];
+}
+
+message EditionsResponse {
+    enum NestedEnum {
+        option features.enum_type = CLOSED;
+        NESTED_ENUM_VALUE_UNSPECIFIED = 0;
+    }
+
+    NestedEnum enum = 1 [ features.field_presence = EXPLICIT ];
+}
+
+service EditionsService {
+    rpc Editions(EditionsRequest) returns (EditionsResponse) {}
+}

protoc-gen-connect-kotlin/src/main/kotlin/com/connectrpc/protocgen/connect/Generator.kt

@@ -95,6 +95,21 @@ class Generator : CodeGenerator {
         }
     }
 
+    override fun getSupportedFeatures(): Array<PluginProtos.CodeGeneratorResponse.Feature> {
+        return arrayOf(
+            PluginProtos.CodeGeneratorResponse.Feature.FEATURE_PROTO3_OPTIONAL,
+            PluginProtos.CodeGeneratorResponse.Feature.FEATURE_SUPPORTS_EDITIONS,
+        )
+    }
+
+    override fun getMinimumEdition(): DescriptorProtos.Edition {
+        return DescriptorProtos.Edition.EDITION_PROTO2
+    }
+
+    override fun getMaximumEdition(): DescriptorProtos.Edition {
+        return DescriptorProtos.Edition.EDITION_2023
+    }
+
     private fun parseFile(file: Descriptors.FileDescriptor): Map<ClassName, FileSpec> {
         val baseSourceInfo = SourceInfo(protoFileMap[file.name]!!, descriptorSource, emptyList())
         val fileSpecs = mutableMapOf<ClassName, FileSpec>()

protoc-gen-connect-kotlin/src/main/kotlin/com/connectrpc/protocgen/connect/internal/CodeGenerator.kt

@@ -15,6 +15,7 @@
 package com.connectrpc.protocgen.connect.internal
 
 import com.connectrpc.protocgen.connect.internal.Plugin.DescriptorSource
+import com.google.protobuf.DescriptorProtos.Edition
 import com.google.protobuf.compiler.PluginProtos
 
 /**
@@ -30,4 +31,21 @@ interface CodeGenerator {
         descriptorSource: DescriptorSource,
         response: Plugin.Response,
     )
+
+    /**
+     * Returns an array of supported Protobuf features.
+     */
+    fun getSupportedFeatures(): Array<PluginProtos.CodeGeneratorResponse.Feature>
+
+    /**
+     * Returns the minimum edition (inclusive) supported by this generator. Any
+     * proto files with an edition before this will result in an error.
+     */
+    fun getMinimumEdition(): Edition
+
+    /**
+     * Returns the maximum edition (inclusive) supported by this generator. Any
+     * proto files with an edition after this will result in an error.
+     */
+    fun getMaximumEdition(): Edition
 }

protoc-gen-connect-kotlin/src/main/kotlin/com/connectrpc/protocgen/connect/internal/Plugin.kt

@@ -109,10 +109,12 @@ object Plugin {
         try {
             // go ahead and write response preamble
             PluginProtos.CodeGeneratorResponse
-                .newBuilder() // add more here as more features are introduced and then supported
+                .newBuilder()
                 .setSupportedFeatures(
-                    toFeatureBitmask(PluginProtos.CodeGeneratorResponse.Feature.FEATURE_PROTO3_OPTIONAL),
+                    toFeatureBitmask(*generator.getSupportedFeatures()),
                 )
+                .setMinimumEdition(generator.getMinimumEdition().number)
+                .setMaximumEdition(generator.getMaximumEdition().number)
                 .build()
                 .writeTo(output)
         } catch (e: IOException) {