[Workspace] Introduce a new package state - usesLibrary

All non-edited packages are eligible to use a provided library
based on the dependency resolution information.

`.usesLibrary` state would result in a new `.providedLibrary`
managed dependency injected into workspace state instead of
a regular local/remote package.

Author: xedin

Sources/Commands/PackageCommands/Update.swift

@@ -73,7 +73,7 @@ extension SwiftPackageCommand {
                 case .removed:
                     report += "\n"
                     report += "- \(package.identity) \(currentVersion)"
-                case .unchanged:
+                case .unchanged, .usesLibrary:
                     continue
                 }
             }

Sources/Workspace/ManagedDependency.swift

@@ -153,15 +153,11 @@ extension Workspace {
 
         public static func providedLibrary(
             packageRef: PackageReference,
-            version: Version
+            library: ProvidedLibrary
         ) throws -> ManagedDependency {
-            guard case .providedLibrary(_, let path) = packageRef.kind else {
-                throw InternalError("invalid package type: \(packageRef.kind)")
-            }
-
-            return ManagedDependency(
+            ManagedDependency(
                 packageRef: packageRef,
-                state: .providedLibrary(at: path, version: version),
+                state: .providedLibrary(at: library.location, version: library.version),
                 subpath: try RelativePath(validating: packageRef.identity.description)
             )
         }

Sources/Workspace/Workspace+Dependencies.swift

@@ -672,7 +672,7 @@ extension Workspace {
                 metadata: packageRef.diagnosticsMetadata
             ).trap {
                 switch state {
-                case .added, .updated, .unchanged:
+                case .added, .updated, .unchanged, .usesLibrary:
                     break
                 case .removed:
                     try self.remove(package: packageRef)
@@ -701,12 +701,27 @@ extension Workspace {
                         productFilter: state.products,
                         observabilityScope: observabilityScope
                     )
-                case .removed, .unchanged:
+                case .removed, .unchanged, .usesLibrary:
                     break
                 }
             }
         }
 
+        // Handle provided libraries
+        for (packageRef, state) in packageStateChanges {
+            observabilityScope.makeChildScope(
+                description: "adding provided libraries",
+                metadata: packageRef.diagnosticsMetadata
+            ).trap {
+                if case .usesLibrary(let library) = state {
+                    try self.state.dependencies.add(
+                        .providedLibrary(packageRef: packageRef, library: library)
+                    )
+                    try self.state.save()
+                }
+            }
+        }
+
         // Inform the delegate if nothing was updated.
         if packageStateChanges.filter({ $0.1 == .unchanged }).count == packageStateChanges.count {
             delegate?.dependenciesUpToDate()
@@ -763,19 +778,6 @@ extension Workspace {
                     state: .custom(version: version, path: path),
                     subpath: RelativePath(validating: "")
                 )
-                self.state.dependencies.add(dependency)
-                try self.state.save()
-                return path
-            } else if let libraryContainer = container as? ProvidedLibraryPackageContainer {
-                guard case .providedLibrary(_, let path) = libraryContainer.package.kind else {
-                    throw InternalError("invalid container for \(package.identity) of type \(package.kind)")
-                }
-
-                let dependency: ManagedDependency = try .providedLibrary(
-                    packageRef: libraryContainer.package,
-                    version: version
-                )
-
                 self.state.dependencies.add(dependency)
                 try self.state.save()
                 return path
@@ -960,6 +962,9 @@ extension Workspace {
         /// The package is updated.
         case updated(State)
 
+        /// The package is replaced with a prebuilt library
+        case usesLibrary(ProvidedLibrary)
+
         public var description: String {
             switch self {
             case .added(let requirement):
@@ -970,15 +975,17 @@ extension Workspace {
                 return "unchanged"
             case .updated(let requirement):
                 return "updated(\(requirement))"
+            case .usesLibrary(let library):
+                return "usesLibrary(\(library.metadata.productName))"
             }
         }
 
         public var isAddedOrUpdated: Bool {
             switch self {
             case .added, .updated:
-                return true
-            case .unchanged, .removed:
-                return false
+                true
+            case .unchanged, .removed, .usesLibrary:
+                false
             }
         }
     }
@@ -1096,18 +1103,20 @@ extension Workspace {
                     packageStateChanges[binding.package.identity] = (binding.package, .added(newState))
                 }
 
-            case .version(let version, _):
-                let stateChange: PackageStateChange
-                switch currentDependency?.state {
+            case .version(let version, let library):
+                let stateChange: PackageStateChange = switch currentDependency?.state {
                 case .sourceControlCheckout(.version(version, _)),
-                        .registryDownload(version),
-                        .providedLibrary(_, version: version),
-                        .custom(version, _):
-                    stateChange = .unchanged
+                     .registryDownload(version),
+                     .providedLibrary(_, version: version),
+                     .custom(version, _):
+                    library.flatMap { .usesLibrary($0) } ?? .unchanged
                 case .edited, .fileSystem, .sourceControlCheckout, .registryDownload, .providedLibrary, .custom:
-                    stateChange = .updated(.init(requirement: .version(version), products: binding.products))
+                    .updated(.init(requirement: .version(version), products: binding.products))
                 case nil:
-                    stateChange = .added(.init(requirement: .version(version), products: binding.products))
+                    library.flatMap { .usesLibrary($0) } ?? .added(.init(
+                        requirement: .version(version),
+                        products: binding.products
+                    ))
                 }
                 packageStateChanges[binding.package.identity] = (binding.package, stateChange)
             }