Add structured swift represntation for the generated metadata

Motivation:

The code gen as it stands tests too much in one go: a small change leads
to many tests being updated. This stems from the translator not being
very testable. To improve this, and make future code gen changes less
painful, we can refactor it such that helpers build structured swift.
These are significantly less coupled and can be tested more easily.

The strategy here is to add all the structured representations for the
metadata, client, and server and then cut over the translators to using
the new code. This first change will introduce the structured
represntation for metadata.

Modifications:

- Add metadata structured swift
- Add helpers for commonly used types

Result:

Metadata is in place

Sources/GRPCCodeGen/Internal/StructuredSwift+ServiceMetadata.swift

@@ -0,0 +1,304 @@
+/*
+ * Copyright 2024, gRPC Authors All rights reserved.
+ *
+ * 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.
+ */
+
+extension TypealiasDescription {
+  /// `typealias Input = <name>`
+  package static func methodInput(
+    accessModifier: AccessModifier? = nil,
+    name: String
+  ) -> Self {
+    return TypealiasDescription(
+      accessModifier: accessModifier,
+      name: "Input",
+      existingType: .member(name)
+    )
+  }
+
+  /// `typealias Output = <name>`
+  package static func methodOutput(
+    accessModifier: AccessModifier? = nil,
+    name: String
+  ) -> Self {
+    return TypealiasDescription(
+      accessModifier: accessModifier,
+      name: "Output",
+      existingType: .member(name)
+    )
+  }
+}
+
+extension VariableDescription {
+  /// ```
+  /// static let descriptor = GRPCCore.MethodDescriptor(
+  ///   service: <serviceNamespace>.descriptor.fullyQualifiedService,
+  ///   method: "<literalMethodName>"
+  /// ```
+  package static func methodDescriptor(
+    accessModifier: AccessModifier? = nil,
+    serviceNamespace: String,
+    literalMethodName: String
+  ) -> Self {
+    return VariableDescription(
+      accessModifier: accessModifier,
+      isStatic: true,
+      kind: .let,
+      left: .identifier(.pattern("descriptor")),
+      right: .functionCall(
+        FunctionCallDescription(
+          calledExpression: .identifierType(.methodDescriptor),
+          arguments: [
+            FunctionArgumentDescription(
+              label: "service",
+              expression: .identifierType(
+                .member([serviceNamespace, "descriptor"])
+              ).dot("fullyQualifiedService")
+            ),
+            FunctionArgumentDescription(
+              label: "method",
+              expression: .literal(literalMethodName)
+            ),
+          ]
+        )
+      )
+    )
+  }
+
+  /// ```
+  /// static let descriptor = GRPCCore.ServiceDescriptor.<namespacedProperty>
+  /// ```
+  package static func serviceDescriptor(
+    accessModifier: AccessModifier? = nil,
+    namespacedProperty: String
+  ) -> Self {
+    return VariableDescription(
+      accessModifier: accessModifier,
+      isStatic: true,
+      kind: .let,
+      left: .identifierPattern("descriptor"),
+      right: .identifier(.type(.serviceDescriptor)).dot(namespacedProperty)
+    )
+  }
+}
+
+extension ExtensionDescription {
+  /// ```
+  /// extension GRPCCore.ServiceDescriptor {
+  ///   static let <PropertyName> = Self(
+  ///     package: "<LiteralNamespaceName>",
+  ///     service: "<LiteralServiceName>"
+  ///   )
+  /// }
+  /// ```
+  package static func serviceDescriptor(
+    accessModifier: AccessModifier? = nil,
+    propertyName: String,
+    literalNamespace: String,
+    literalService: String
+  ) -> ExtensionDescription {
+    return ExtensionDescription(
+      onType: "GRPCCore.ServiceDescriptor",
+      declarations: [
+        .variable(
+          accessModifier: accessModifier,
+          isStatic: true,
+          kind: .let,
+          left: .identifier(.pattern(propertyName)),
+          right: .functionCall(
+            calledExpression: .identifierType(.member("Self")),
+            arguments: [
+              FunctionArgumentDescription(
+                label: "package",
+                expression: .literal(literalNamespace)
+              ),
+              FunctionArgumentDescription(
+                label: "service",
+                expression: .literal(literalService)
+              ),
+            ]
+          )
+        )
+      ]
+    )
+  }
+}
+
+extension VariableDescription {
+  /// ```
+  /// static let descriptors: [GRPCCore.MethodDescriptor] = [<Name1>.descriptor, ...]
+  /// ```
+  package static func methodDescriptorsArray(
+    accessModifier: AccessModifier? = nil,
+    methodNamespaceNames names: [String]
+  ) -> Self {
+    return VariableDescription(
+      accessModifier: accessModifier,
+      isStatic: true,
+      kind: .let,
+      left: .identifier(.pattern("descriptors")),
+      type: .array(.methodDescriptor),
+      right: .literal(.array(names.map { name in .identifierPattern(name).dot("descriptor") }))
+    )
+  }
+}
+
+extension EnumDescription {
+  /// ```
+  /// enum <Method> {
+  ///   typealias Input = <InputType>
+  ///   typealias Output = <OutputType>
+  ///   static let descriptor = GRPCCore.MethodDescriptor(
+  ///     service: <ServiceNamespace>.descriptor.fullyQualifiedService,
+  ///     method: "<LiteralMethod>"
+  ///   )
+  /// }
+  /// ```
+  package static func methodNamespace(
+    accessModifier: AccessModifier? = nil,
+    name: String,
+    literalMethod: String,
+    serviceNamespace: String,
+    inputType: String,
+    outputType: String
+  ) -> Self {
+    return EnumDescription(
+      accessModifier: accessModifier,
+      name: name,
+      members: [
+        .typealias(.methodInput(accessModifier: accessModifier, name: inputType)),
+        .typealias(.methodOutput(accessModifier: accessModifier, name: outputType)),
+        .variable(
+          .methodDescriptor(
+            accessModifier: accessModifier,
+            serviceNamespace: serviceNamespace,
+            literalMethodName: literalMethod
+          )
+        ),
+      ]
+    )
+  }
+
+  /// ```
+  /// enum Method {
+  ///   enum <Method> {
+  ///     typealias Input = <MethodInput>
+  ///     typealias Output = <MethodOutput>
+  ///     static let descriptor = GRPCCore.MethodDescriptor(
+  ///       service: <serviceNamespaceName>.descriptor.fullyQualifiedService,
+  ///       method: "<Method>"
+  ///     )
+  ///   }
+  ///   ...
+  ///   static let descriptors: [GRPCCore.MethodDescriptor] = [
+  ///     <Method>.descriptor,
+  ///     ...
+  ///   ]
+  /// }
+  /// ```
+  package static func methodsNamespace(
+    accessModifier: AccessModifier? = nil,
+    serviceNamespace: String,
+    methods: [MethodDescriptor]
+  ) -> EnumDescription {
+    var description = EnumDescription(accessModifier: accessModifier, name: "Method")
+
+    // Add a namespace for each method.
+    let methodNamespaces: [Declaration] = methods.map { method in
+      return .enum(
+        .methodNamespace(
+          accessModifier: accessModifier,
+          name: method.name.base,
+          literalMethod: method.name.base,
+          serviceNamespace: serviceNamespace,
+          inputType: method.inputType,
+          outputType: method.outputType
+        )
+      )
+    }
+    description.members.append(contentsOf: methodNamespaces)
+
+    // Add an array of method descriptors
+    let methodDescriptorsArray: VariableDescription = .methodDescriptorsArray(
+      accessModifier: accessModifier,
+      methodNamespaceNames: methods.map { $0.name.base }
+    )
+    description.members.append(.variable(methodDescriptorsArray))
+
+    return description
+  }
+
+  /// ```
+  /// enum <Name> {
+  ///   static let descriptor = GRPCCore.ServiceDescriptor.<namespacedServicePropertyName>
+  ///   enum Method {
+  ///     ...
+  ///   }
+  ///   @available(...)
+  ///   typealias StreamingServiceProtocol = ...
+  ///   @available(...)
+  ///   typealias ServiceProtocol = ...
+  ///   ...
+  /// }
+  /// ```
+  package static func serviceNamespace(
+    accessModifier: AccessModifier? = nil,
+    name: String,
+    serviceDescriptorProperty: String,
+    client: Bool,
+    server: Bool,
+    methods: [MethodDescriptor]
+  ) -> EnumDescription {
+    var description = EnumDescription(accessModifier: accessModifier, name: name)
+
+    // static let descriptor = GRPCCore.ServiceDescriptor.<namespacedServicePropertyName>
+    let descriptor = VariableDescription.serviceDescriptor(
+      accessModifier: accessModifier,
+      namespacedProperty: serviceDescriptorProperty
+    )
+    description.members.append(.variable(descriptor))
+
+    // enum Method { ... }
+    let methodsNamespace: EnumDescription = .methodsNamespace(
+      accessModifier: accessModifier,
+      serviceNamespace: name,
+      methods: methods
+    )
+    description.members.append(.enum(methodsNamespace))
+
+    // Typealiases for the various protocols.
+    var typealiasNames: [String] = []
+    if server {
+      typealiasNames.append("StreamingServiceProtocol")
+      typealiasNames.append("ServiceProtocol")
+    }
+    if client {
+      typealiasNames.append("ClientProtocol")
+      typealiasNames.append("Client")
+    }
+    let typealiases: [Declaration] = typealiasNames.map { alias in
+      .guarded(
+        .grpc,
+        .typealias(
+          accessModifier: accessModifier,
+          name: alias,
+          existingType: .member(name + "_" + alias)
+        )
+      )
+    }
+    description.members.append(contentsOf: typealiases)
+
+    return description
+  }
+}

Sources/GRPCCodeGen/Internal/StructuredSwift+Types.swift

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2024, gRPC Authors All rights reserved.
+ *
+ * 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.
+ */
+
+extension AvailabilityDescription {
+  package static let grpc = AvailabilityDescription(
+    osVersions: [
+      OSVersion(os: .macOS, version: "15.0"),
+      OSVersion(os: .iOS, version: "18.0"),
+      OSVersion(os: .watchOS, version: "11.0"),
+      OSVersion(os: .tvOS, version: "18.0"),
+      OSVersion(os: .visionOS, version: "2.0"),
+    ]
+  )
+}
+
+extension ExistingTypeDescription {
+  fileprivate static func grpcCore(_ typeName: String) -> Self {
+    return .member(["GRPCCore", typeName])
+  }
+
+  fileprivate static func requestResponse(
+    for type: String?,
+    isRequest: Bool,
+    isStreaming: Bool,
+    isClient: Bool
+  ) -> Self {
+    let prefix = isStreaming ? "Streaming" : ""
+    let peer = isClient ? "Client" : "Server"
+    let kind = isRequest ? "Request" : "Response"
+    let baseType: Self = .grpcCore(prefix + peer + kind)
+
+    if let type = type {
+      return .generic(wrapper: baseType, wrapped: .member(type))
+    } else {
+      return baseType
+    }
+  }
+
+  package static func serverRequest(forType type: String?, streaming: Bool) -> Self {
+    return .requestResponse(for: type, isRequest: true, isStreaming: streaming, isClient: false)
+  }
+
+  package static func serverResponse(forType type: String?, streaming: Bool) -> Self {
+    return .requestResponse(for: type, isRequest: false, isStreaming: streaming, isClient: false)
+  }
+
+  package static func clientRequest(forType type: String?, streaming: Bool) -> Self {
+    return .requestResponse(for: type, isRequest: true, isStreaming: streaming, isClient: true)
+  }
+
+  package static func clientResponse(forType type: String?, streaming: Bool) -> Self {
+    return .requestResponse(for: type, isRequest: false, isStreaming: streaming, isClient: true)
+  }
+
+  package static let serverContext: Self = .grpcCore("ServerContext")
+  package static let rpcRouter: Self = .grpcCore("RPCRouter")
+  package static let serviceDescriptor: Self = .grpcCore("ServiceDescriptor")
+  package static let methodDescriptor: Self = .grpcCore("MethodDescriptor")
+
+  package static func serializer(forType type: String) -> Self {
+    .generic(wrapper: .grpcCore("MessageSerializer"), wrapped: .member(type))
+  }
+
+  package static func deserializer(forType type: String) -> Self {
+    .generic(wrapper: .grpcCore("MessageDeserializer"), wrapped: .member(type))
+  }
+
+  package static func rpcWriter(forType type: String) -> Self {
+    .generic(wrapper: .grpcCore("RPCWriter"), wrapped: .member(type))
+  }
+
+  package static let callOptions: Self = .grpcCore("CallOptions")
+  package static let metadata: Self = .grpcCore("Metadata")
+  package static let grpcClient: Self = .grpcCore("GRPCClient")
+}