Refactor manifest serialization (#6145)

This is a fairly large change to refactor the manifest serialization to achieve two goals: get rid of the custom deserialization in `ManifestJSONParser` to use `Codable` throughout and decouple the user-facing `PackageDescription` model from its serialization.

- Use `Codable` for `ManifestJSONParser`
- Remove `Codable` conformances from public facing PD types and create a private serialization model in `PackageDescriptionSerialization` that can be used for reading and writing

Both of these have to happen in a single PR because of a few glaring issues with making the PD model fully codable.

There is further work here which can happen in subsequent PRs:

- Relocate business logic from `ManifestJSONParser` into `PackageModel` as much as possible
- Evaluate the existence of `TargetDescription` etc - it feels like we should be able to get rid of one layer of model objects here, potentially
- Evaluate other serialization code in SwiftPM, e.g. for `package describe`, the `ManifestSourceGeneration` stuff etc

Author: neonichu

Sources/Basics/Observability.swift

@@ -289,6 +289,8 @@ public struct Diagnostic: CustomStringConvertible {
             message = "\(diagnosticData)"
         } else if let convertible = error as? DiagnosticDataConvertible {
             message = "\(convertible.diagnosticData)"
+        } else if let decodingError = error as? DecodingError { // special case because `LocalizedError` conversion will hide the underlying error
+            message = "\(error)"
         } else if let localizedError = error as? LocalizedError {
             message = localizedError.errorDescription ?? localizedError.localizedDescription
         } else {

Sources/PackageDescription/BuildSettings.swift

@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 /// The build configuration such as debug or release.
-public struct BuildConfiguration: Encodable {
-    private let config: String
+public struct BuildConfiguration {
+    let config: String
 
     private init(_ config: String) {
         self.config = config
@@ -53,10 +53,9 @@ public struct BuildConfiguration: Encodable {
 ///     ]
 /// ),
 /// ```
-public struct BuildSettingCondition: Encodable {
-
-    private let platforms: [Platform]?
-    private let config: BuildConfiguration?
+public struct BuildSettingCondition {
+    let platforms: [Platform]?
+    let config: BuildConfiguration?
 
     private init(platforms: [Platform]?, config: BuildConfiguration?) {
         self.platforms = platforms
@@ -100,7 +99,7 @@ public struct BuildSettingCondition: Encodable {
 }
 
 /// The underlying build setting data.
-fileprivate struct BuildSettingData: Encodable {
+struct BuildSettingData {
 
     /// The name of the build setting.
     let name: String
@@ -113,8 +112,8 @@ fileprivate struct BuildSettingData: Encodable {
 }
 
 /// A C-language build setting.
-public struct CSetting: Encodable {
-    private let data: BuildSettingData
+public struct CSetting {
+    let data: BuildSettingData
 
     private init(name: String, value: [String], condition: BuildSettingCondition?) {
         self.data = BuildSettingData(name: name, value: value, condition: condition)
@@ -179,8 +178,8 @@ public struct CSetting: Encodable {
 }
 
 /// A CXX-language build setting.
-public struct CXXSetting: Encodable {
-    private let data: BuildSettingData
+public struct CXXSetting {
+    let data: BuildSettingData
 
     private init(name: String, value: [String], condition: BuildSettingCondition?) {
         self.data = BuildSettingData(name: name, value: value, condition: condition)
@@ -244,8 +243,8 @@ public struct CXXSetting: Encodable {
 }
 
 /// A Swift language build setting.
-public struct SwiftSetting: Encodable {
-    private let data: BuildSettingData
+public struct SwiftSetting {
+    let data: BuildSettingData
 
     private init(name: String, value: [String], condition: BuildSettingCondition?) {
         self.data = BuildSettingData(name: name, value: value, condition: condition)
@@ -348,8 +347,8 @@ public struct SwiftSetting: Encodable {
 }
 
 /// A linker build setting.
-public struct LinkerSetting: Encodable {
-    private let data: BuildSettingData
+public struct LinkerSetting {
+    let data: BuildSettingData
 
     private init(name: String, value: [String], condition: BuildSettingCondition?) {
         self.data = BuildSettingData(name: name, value: value, condition: condition)

Sources/PackageDescription/CMakeLists.txt

@@ -13,6 +13,7 @@ add_library(PackageDescription
   LanguageStandardSettings.swift
   PackageDescription.swift
   PackageDescriptionSerialization.swift
+  PackageDescriptionSerializationConversion.swift
   PackageDependency.swift
   PackageRequirement.swift
   Product.swift

Sources/PackageDescription/LanguageStandardSettings.swift

@@ -12,7 +12,7 @@
 
 /// The supported C language standard you use to compile C sources in the
 /// package.
-public enum CLanguageStandard: String, Encodable {
+public enum CLanguageStandard: String {
 
     /// The identifier for the ISO C 1990 language standard.
     case c89
@@ -89,7 +89,7 @@ public enum CLanguageStandard: String, Encodable {
 /// Aliases are available for some C++ language standards. For example,
 /// use `cxx98` or `cxx03` for the "ISO C++ 1998 with amendments" standard.
 /// To learn more, see [C++ Support in Clang](https://clang.llvm.org/cxx_status.html).
-public enum CXXLanguageStandard: String, Encodable {
+public enum CXXLanguageStandard: String {
 
     /// The identifier for the ISO C++ 1998 language standard with amendments.
     case cxx98 = "c++98"

Sources/PackageDescription/PackageDependency.swift

@@ -10,9 +10,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-@_implementationOnly import Foundation
-
-// MARK: - file system
 
 extension Package {
     /// A package dependency of a Swift package.
@@ -27,7 +24,7 @@ extension Package {
     /// package. If you add the Swift package as a package dependency to an app
     /// for an Apple platform, you can find the `Package.resolved` file inside
     /// your `.xcodeproj` or `.xcworkspace`.
-    public class Dependency: Encodable {
+    public class Dependency {
         /// The kind of dependency.
         @available(_PackageDescription, introduced: 5.6)
         public enum Kind {

Sources/PackageDescription/PackageDescription.swift

@@ -438,14 +438,15 @@ public enum SystemPackageProvider {
 // MARK: - Package Dumping
 
 func manifestToJSON(_ package: Package) -> String {
-    struct Output: Encodable {
-        let package: Package
+    struct Output: Codable {
+        let package: Serialization.Package
         let errors: [String]
+        let version: Int
     }
 
     let encoder = JSONEncoder()
     encoder.outputFormatting = [.sortedKeys, .withoutEscapingSlashes]
-    let data = try! encoder.encode(Output(package: package, errors: errors))
+    let data = try! encoder.encode(Output(package: .init(package), errors: errors, version: 2))
     return String(data: data, encoding: .utf8)!
 }