Add support for package visibility modifier

Documentation/PLUGIN.md

@@ -119,6 +119,8 @@ The possible values for `Visibility` are:
 
 * `Internal` (default): No visibility is set for the types, so they get the
   default internal visibility.
+* `Package` (Swift 5.9 or later required): The visibility on the types is set to
+ `package` so the types will be exposed across the whole Swift package they belong to.
 * `Public`: The visibility on the types is set to `public` so the types will
   be exposed outside the module they are compiled into.
 

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.8
+// swift-tools-version:5.9
 
 // Package.swift
 //

Package@swift-5.7.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.6
+// swift-tools-version:5.7
 
 // Package.swift
 //

Package@swift-5.8.swift

@@ -0,0 +1,91 @@
+// swift-tools-version:5.8
+
+// Package.swift
+//
+// Copyright (c) 2014 - 2018 Apple Inc. and the project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See LICENSE.txt for license information:
+// https://github.com/apple/swift-protobuf/blob/main/LICENSE.txt
+//
+
+import PackageDescription
+
+let package = Package(
+  name: "SwiftProtobuf",
+  products: [
+    .executable(
+        name: "protoc-gen-swift",
+        targets: ["protoc-gen-swift"]
+    ),
+    .library(
+        name: "SwiftProtobuf",
+        targets: ["SwiftProtobuf"]
+    ),
+    .library(
+        name: "SwiftProtobufPluginLibrary",
+        targets: ["SwiftProtobufPluginLibrary"]
+    ),
+    .plugin(
+        name: "SwiftProtobufPlugin",
+        targets: ["SwiftProtobufPlugin"]
+    ),
+  ],
+  dependencies: [
+    .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
+  ],
+  targets: [
+    .target(
+        name: "SwiftProtobuf",
+        exclude: ["CMakeLists.txt"],
+        swiftSettings: [
+          .enableExperimentalFeature("StrictConcurrency=complete"),
+        ]
+    ),
+    .target(
+        name: "SwiftProtobufPluginLibrary",
+        dependencies: ["SwiftProtobuf"],
+        exclude: ["CMakeLists.txt"]
+    ),
+    .target(
+        name: "SwiftProtobufTestHelpers",
+        dependencies: ["SwiftProtobuf"],
+        swiftSettings: [
+          .enableExperimentalFeature("StrictConcurrency=complete"),
+        ]
+    ),
+    .executableTarget(
+        name: "protoc-gen-swift",
+        dependencies: ["SwiftProtobufPluginLibrary", "SwiftProtobuf"],
+        exclude: ["CMakeLists.txt"]
+    ),
+    .executableTarget(
+        name: "Conformance",
+        dependencies: ["SwiftProtobuf"],
+        exclude: ["failure_list_swift.txt", "text_format_failure_list_swift.txt"]
+    ),
+    .plugin(
+        name: "SwiftProtobufPlugin",
+        capability: .buildTool(),
+        dependencies: [
+            "protoc-gen-swift"
+        ]
+    ),
+    .testTarget(
+        name: "SwiftProtobufTests",
+        dependencies: ["SwiftProtobuf"],
+        swiftSettings: [
+          .enableExperimentalFeature("StrictConcurrency=complete"),
+        ]
+    ),
+    .testTarget(
+        name: "SwiftProtobufPluginLibraryTests",
+        dependencies: ["SwiftProtobufPluginLibrary", "SwiftProtobufTestHelpers"]
+    ),
+    .testTarget(
+        name: "protoc-gen-swiftTests",
+        dependencies: ["protoc-gen-swift", "SwiftProtobufTestHelpers"]
+    ),
+  ],
+  swiftLanguageVersions: [.v5]
+)

Plugins/SwiftProtobufPlugin/plugin.swift

@@ -37,13 +37,18 @@ struct SwiftProtobufPlugin {
                 case `internal` = "Internal"
                 /// The generated files should have `public` access level.
                 case `public` = "Public"
+                /// The generated files should have `package` access level.
+                /// - Note: Swift 5.9 or later is needed to use this option.
+                case `package` = "Package"
 
                 init?(rawValue: String) {
                     switch rawValue.lowercased() {
                     case "internal":
                         self = .internal
                     case "public":
                         self = .public
+                    case "package":
+                        self = .package
                     default:
                         return nil
                     }

Sources/protoc-gen-swift/GeneratorOptions.swift

@@ -33,13 +33,16 @@ class GeneratorOptions {
   enum Visibility {
     case `internal`
     case `public`
+    case `package`
 
     init?(flag: String) {
       switch flag.lowercased() {
       case "internal":
         self = .internal
       case "public":
         self = .public
+      case "package":
+        self = .package
       default:
         return nil
       }
@@ -119,6 +122,8 @@ class GeneratorOptions {
       visibilitySourceSnippet = ""
     case .public:
       visibilitySourceSnippet = "public "
+    case .package:
+      visibilitySourceSnippet = "package "
     }
 
     self.implementationOnlyImports = implementationOnlyImports