Merge pull request #20 from drewmccormack/feature/salvaging

Introduce “salvaging” (2-way merge) for bootstrapping

Author: drewmccormack

Samples/Forkers/Forkers/Models/Forker.swift

@@ -30,3 +30,18 @@ struct Forker: Identifiable, Codable, Hashable {
     @Merged var notes: String = ""
     @Merged var tags: Set<String> = []
 }
+
+extension Forkers {
+    
+    func salvaging(from other: Forkers) throws -> Forkers {
+        // When two devices have unrelated histories, they can't be
+        // 3-way merged. Instead, we will start with the dominant
+        // forker values (eg from the cloud), and copy in any forkers unique
+        // to the subordinate data (eg local)
+        var new = self
+        let ids = Set(self.forkers.map(\.id))
+        new.forkers += other.forkers.filter { !ids.contains($0.id) }
+        return new
+    }
+    
+}

Sources/Forked/ForkedResource+Merging.swift

@@ -96,10 +96,13 @@ public extension ForkedResource where RepositoryType.Resource: Mergeable {
         switch (commits.dominant.content, commits.subordinate.content, ancestorCommit.content) {
         case (.none, .none, _):
             return .none
-        case (.resource, .none, _), (.resource, .resource, .none):
+        case (.resource, .none, _):
             return commits.dominant.content
         case (.none, .resource, _):
             return commits.subordinate.content
+        case (.resource(let r1), .resource(let r2), .none):
+            let resource = try r1.salvaging(from: r2)
+            return .resource(resource)
         case (.resource(let r1), .resource(let r2), .resource(let ra)):
             let resource = try r1.merged(withSubordinate: r2, commonAncestor: ra)
             return .resource(resource)