refactor serialization and state management

motivation: stronger seperation between state managment format and data model, allowing evolution of storeage format

changes:
* refactor PinsStore, RepositoryManager, and WorkspaceState to model their state storage seperately from the data model
* use Codable instead of JSONMappable/JSONSerializable/SimplePersistence
* adjust call-sites and tests where necessary

Author: tomerd

Package.resolved.lock

@@ -11,6 +11,7 @@
 import class Foundation.DateFormatter
 import class Foundation.JSONDecoder
 import class Foundation.JSONEncoder
+import TSCBasic
 
 #if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
 extension DateFormatter {
@@ -112,3 +113,11 @@ extension JSONEncoder {
         return encoder
     }
 }
+
+extension JSONDecoder {
+    public func decode<T: Decodable>(path: AbsolutePath, fileSystem: FileSystem, `as` kind: T.Type) throws -> T {
+        try fileSystem.readFileContents(path).withData { data in
+            try self.decode(kind, from: data)
+        }
+    }
+}

Sources/Basics/JSON+Extensions.swift

@@ -71,52 +71,3 @@ extension CheckoutState: CustomStringConvertible {
         }
     }
 }
-
-// MARK: - JSON
-
-extension CheckoutState: JSONMappable, JSONSerializable {
-    public init(json: JSON) throws {
-        let revision: Revision = try json.get("revision")
-        let version: Version? = json.get("version")
-        let branch: String? = json.get("branch")
-
-        switch (version, branch) {
-        case (.none, .none):
-            self = .revision(revision)
-        case (.some(let version), .none):
-            self = .version(version, revision: revision)
-        case (.none, .some(let branch)):
-            self = .branch(name: branch, revision: revision)
-        case (.some(_), .some(_)):
-            preconditionFailure("Can't set both branch and version.")
-        }
-    }
-
-    public func toJSON() -> JSON {
-        let revision: Revision
-        let version: Version?
-        let branch: String?
-
-        switch self {
-        case .revision(let _revision):
-            revision = _revision
-            version = nil
-            branch = nil
-        case .version(let _version, let _revision):
-            revision = _revision
-            version = _version
-            branch = nil
-        case .branch(let _branch, let _revision):
-            revision = _revision
-            version = nil
-            branch = _branch
-        }
-
-        return .init([
-            "revision": revision.identifier,
-            "version": version.toJSON(),
-            "branch": branch.toJSON(),
-        ])
-    }
-}
-