Enhancement: Add ability to print Combine.Publisher flow.

Documentation/MVVMDemo/MVVMDemo.xcodeproj/project.pbxproj

@@ -461,6 +461,7 @@
 				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = 1;
 				DEVELOPMENT_ASSET_PATHS = "\"MVVMDemo/Preview Content\"";
+				DEVELOPMENT_TEAM = "";
 				ENABLE_PREVIEWS = YES;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;
@@ -489,6 +490,7 @@
 				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = 1;
 				DEVELOPMENT_ASSET_PATHS = "\"MVVMDemo/Preview Content\"";
+				DEVELOPMENT_TEAM = "";
 				ENABLE_PREVIEWS = YES;
 				GENERATE_INFOPLIST_FILE = YES;
 				INFOPLIST_KEY_UIApplicationSceneManifest_Generation = YES;

Documentation/QueryDemo/QueryDemo/Views/AppView.swift

@@ -10,7 +10,7 @@ struct AppView: View {
         var id: Int64
     }
 
-    @Query(AnyPlayerRequest())
+    @Query(AnyPlayerRequest(), printPublisherConfiguration: .init(prefix: "\(#function)"))
     private var player: Player?
 
     @State private var editedPlayer: EditedPlayer?

Sources/GRDBQuery/Query+DatabaseContext.swift

@@ -21,9 +21,12 @@ extension Query where Request.Context == DatabaseContext {
     ///
     /// - parameter request: An initial ``Queryable`` request.
     public init(
-        _ request: Request
+        _ request: Request,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil
     ) {
-        self.init(request, in: \.databaseContext)
+        self.init(request,
+                  in: \.databaseContext,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query` that feeds from the `databaseContext`
@@ -50,9 +53,12 @@ extension Query where Request.Context == DatabaseContext {
     ///
     /// - parameter request: A ``Queryable`` request.
     public init(
-        constant request: Request
+        constant request: Request,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil
     ) {
-        self.init(constant: request, in: \.databaseContext)
+        self.init(constant: request,
+                  in: \.databaseContext,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query` that feeds from the `databaseContext`
@@ -88,8 +94,11 @@ extension Query where Request.Context == DatabaseContext {
     ///
     /// - parameter request: A SwiftUI binding to a ``Queryable`` request.
     public init(
-        _ request: Binding<Request>
+        _ request: Binding<Request>,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil
     ) {
-        self.init(request, in: \.databaseContext)
+        self.init(request,
+                  in: \.databaseContext,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 }

Sources/GRDBQuery/Query+VoidContext.swift

@@ -29,8 +29,11 @@ extension Query where Request.Context == Void {
     /// ```
     ///
     /// - parameter request: An initial ``Queryable`` request.
-    public init(_ request: Request) {
-        self.init(request, in: \.void)
+    public init(_ request: Request,
+                printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil) {
+        self.init(request,
+                  in: \.void,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query`, given a SwiftUI binding to a ``Queryable``
@@ -73,8 +76,11 @@ extension Query where Request.Context == Void {
     /// ```
     ///
     /// - parameter request: A SwiftUI binding to a ``Queryable`` request.
-    public init(_ request: Binding<Request>) {
-        self.init(request, in: \.void)
+    public init(_ request: Binding<Request>,
+                printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil) {
+        self.init(request,
+                  in: \.void,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query`, given a ``Queryable`` request that uses
@@ -109,8 +115,11 @@ extension Query where Request.Context == Void {
     /// ```
     ///
     /// - parameter request: A ``Queryable`` request.
-    public init(constant request: Request) {
-        self.init(constant:request, in: \.void)
+    public init(constant request: Request,
+                printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil) {
+        self.init(constant:request,
+                  in: \.void,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 }
 

Sources/GRDBQuery/Query.swift

@@ -1,6 +1,16 @@
 import Combine
 import SwiftUI
 
+public struct QueryPublisherPrintConfiguration {
+    public let prefix: String
+    public let outputStream: (any TextOutputStream)?
+
+    public init(prefix: String = "", outputStream: (any TextOutputStream)? = nil) {
+        self.prefix = prefix
+        self.outputStream = outputStream
+    }
+}
+
 // See Documentation.docc/Extensions/Query.md
 @propertyWrapper
 @MainActor public struct Query<Request: Queryable> {
@@ -22,7 +32,7 @@ import SwiftUI
 
     /// The `Query` configuration.
     private let configuration: Configuration
-
+    private let printPublisherConfiguration: QueryPublisherPrintConfiguration?
     /// The last published database value.
     public var wrappedValue: Request.Value {
         tracker.value ?? Request.defaultValue
@@ -73,10 +83,12 @@ import SwiftUI
     /// - parameter keyPath: A key path to the database in the environment.
     public init(
         _ request: Request,
-        in keyPath: KeyPath<EnvironmentValues, Request.Context>)
+        in keyPath: KeyPath<EnvironmentValues, Request.Context>,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil)
     {
-        self._database = Environment(keyPath)
-        self.configuration = .initial(request)
+        self.init(configuration: .initial(request),
+                  in: keyPath,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query`, given a ``Queryable`` request, and a key path to
@@ -111,10 +123,12 @@ import SwiftUI
     /// - parameter keyPath: A key path to the database in the environment.
     public init(
         constant request: Request,
-        in keyPath: KeyPath<EnvironmentValues, Request.Context>)
+        in keyPath: KeyPath<EnvironmentValues, Request.Context>,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil)
     {
-        self._database = Environment(keyPath)
-        self.configuration = .constant(request)
+        self.init(configuration: .constant(request),
+                  in: keyPath,
+                  printPublisherConfiguration: printPublisherConfiguration)
     }
 
     /// Creates a `Query`, given a SwiftUI binding to its ``Queryable``
@@ -158,12 +172,25 @@ import SwiftUI
     /// - parameter keyPath: A key path to the database in the environment.
     public init(
         _ request: Binding<Request>,
-        in keyPath: KeyPath<EnvironmentValues, Request.Context>)
+        in keyPath: KeyPath<EnvironmentValues, Request.Context>,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration? = nil)
+    {
+        self.init(configuration: .binding(request),
+                  in: keyPath,
+                  printPublisherConfiguration: printPublisherConfiguration)
+    }
+
+    private init(
+        configuration: Configuration,
+        in keyPath: KeyPath<EnvironmentValues, Request.Context>,
+        printPublisherConfiguration: QueryPublisherPrintConfiguration?)
     {
         self._database = Environment(keyPath)
-        self.configuration = .binding(request)
+        self.configuration = configuration
+        self.printPublisherConfiguration = printPublisherConfiguration
     }
 
+
     /// A wrapper of the underlying `Query` that creates bindings to
     /// its ``Queryable`` request.
     ///
@@ -252,8 +279,10 @@ import SwiftUI
         func update(
             queryObservationEnabled: Bool,
             configuration queryConfiguration: Configuration,
+            printPublisherConfiguration: QueryPublisherPrintConfiguration?,
             database: Request.Context)
         {
+
             // Give up if observation is disabled
             guard queryObservationEnabled else {
                 trackedRequest = nil
@@ -291,9 +320,17 @@ import SwiftUI
                 return
             }
 
+            var finalPublisher = publisher.eraseToAnyPublisher()
+
+            if let printConfiguration = printPublisherConfiguration {
+                finalPublisher = finalPublisher.print(printConfiguration.prefix,
+                                                      to: printConfiguration.outputStream)
+                .eraseToAnyPublisher()
+            }
+
             // Start tracking the new request
             var isUpdating = true
-            cancellable = publisher.sink(
+            cancellable = finalPublisher.sink(
                 receiveCompletion: { [weak self] completion in
                     guard let self = self else { return }
                     MainActor.assumeIsolated {
@@ -335,6 +372,7 @@ extension Query: DynamicProperty {
             tracker.update(
                 queryObservationEnabled: queryObservationEnabled,
                 configuration: configuration,
+                printPublisherConfiguration: printPublisherConfiguration,
                 database: database)
         }
     }