Add #LiveView macro for registering add-on libraries (#1004)

* Add `#LiveView` macro for registering add-on libraries

* Suggest using placeholder types

Author: carson-katri

Sources/LiveViewNative/LiveView.swift

@@ -9,6 +9,26 @@ import Foundation
 import SwiftUI
 import Combine
 
+#if swift(>=5.9)
+/// Create a ``LiveView`` with a list of addons.
+///
+/// Use this macro to automatically register any addons.
+/// Use a placeholder type (`_`) as the root for each registry.
+///
+/// ```swift
+/// #LiveView(.localhost, addons: [ChartsRegistry<_>.self, AVKitRegistry<_>.self])
+/// ```
+///
+/// - Note: This macro erases the underlying ``LiveView`` to `AnyView`.
+/// This may incur a minor performance hit when updating the `View` containing the ``LiveView``.
+@freestanding(expression)
+public macro LiveView<Host: LiveViewHost>(
+    _ host: Host,
+    configuration: LiveSessionConfiguration = .init(),
+    addons: [any CustomRegistry<EmptyRegistry>.Type]
+) -> AnyView = #externalMacro(module: "LiveViewNativeMacros", type: "LiveViewMacro")
+#endif
+
 /// The SwiftUI root view for a Phoenix LiveView.
 ///
 /// The `LiveView` attempts to connect immediately when it appears.

Sources/LiveViewNativeMacros/LiveViewMacro.swift

@@ -0,0 +1,98 @@
+//
+//  LiveViewMacro.swift
+//
+//
+//  Created by Carson Katri on 7/6/23.
+//
+
+import SwiftCompilerPlugin
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public enum LiveViewMacro {}
+
+extension LiveViewMacro: ExpressionMacro {
+    public static func expansion<Node, Context>(
+        of node: Node,
+        in context: Context
+    ) throws -> ExprSyntax where Node : FreestandingMacroExpansionSyntax, Context : MacroExpansionContext {
+        let registryName = context.makeUniqueName("Registry")
+        
+        guard let addons = try node.argumentList.last?
+            .expression.as(ArrayExprSyntax.self)?
+            .elements.map(transformAddon(_:))
+        else { throw LiveViewMacroError.invalidAddonsSyntax }
+        
+        let registries: DeclSyntax
+        switch addons.count {
+        case 0:
+            throw LiveViewMacroError.missingAddons
+        case 1:
+            registries = "typealias Registries = \(addons.first!)"
+        default:
+            func multiRegistry(_ addons: some RandomAccessCollection<SimpleTypeIdentifierSyntax>) -> SimpleTypeIdentifierSyntax {
+                switch addons.count {
+                case 2:
+                    return SimpleTypeIdentifierSyntax(
+                        name: "_MultiRegistry",
+                        genericArgumentClause: .init(arguments: .init([
+                            .init(argumentType: addons.first!, trailingComma: .commaToken()),
+                            .init(argumentType: addons.last!)
+                        ]))
+                    )
+                default:
+                    return SimpleTypeIdentifierSyntax(
+                        name: "_MultiRegistry",
+                        genericArgumentClause: .init(arguments: .init([
+                            .init(argumentType: addons.first!, trailingComma: .commaToken()),
+                            .init(argumentType: multiRegistry(addons.dropFirst()))
+                        ]))
+                    )
+                }
+            }
+            registries = "typealias Registries = \(multiRegistry(addons))"
+        }
+        
+        let liveViewArguments = node.argumentList
+            .removingLast()
+            .replacing(childAt: node.argumentList.count - 2, with: node.argumentList.removingLast().last!.with(\.trailingComma, nil))
+        
+        return """
+        { () -> AnyView in
+            enum \(registryName): AggregateRegistry {
+                \(registries)
+            }
+        
+            return AnyView(LiveView<\(registryName)>(\(liveViewArguments)))
+        }()
+        """
+    }
+    
+    private static func transformAddon(_ element: ArrayElementSyntax) throws -> SimpleTypeIdentifierSyntax {
+        guard let registry = element.expression.as(MemberAccessExprSyntax.self)?.base?.as(SpecializeExprSyntax.self),
+              let name = registry.expression.as(IdentifierExprSyntax.self)
+        else { throw LiveViewMacroError.invalidAddonElement }
+        return SimpleTypeIdentifierSyntax(
+            name: name.identifier,
+            genericArgumentClause: .init(.init(arguments: .init([.init(argumentType: SimpleTypeIdentifierSyntax(name: .identifier("Self")))])))
+        )
+    }
+}
+
+enum LiveViewMacroError: Error, CustomStringConvertible {
+    case invalidAddonsSyntax
+    case invalidAddonElement
+    case missingAddons
+    
+    var description: String {
+        switch self {
+        case .invalidAddonsSyntax:
+            return "Invalid value specified for 'addons'. Expected a static array literal."
+        case .invalidAddonElement:
+            return "Invalid addon provided. Expected a specialized registry type, such as 'AddonRegistry<Self>.self'"
+        case .missingAddons:
+            return "'addons' must not be empty."
+        }
+    }
+}

Sources/LiveViewNativeMacros/LiveViewNativeMacros.swift

@@ -11,6 +11,7 @@ import SwiftSyntaxMacros
 @main
 struct LiveViewNativeMacrosPlugin: CompilerPlugin {
     let providingMacros: [Macro.Type] = [
-        RegistriesMacro.self
+        RegistriesMacro.self,
+        LiveViewMacro.self
     ]
 }

Tests/LiveViewNativeMacrosTests/LiveViewNativeMacrosTests.swift

@@ -12,6 +12,7 @@ import LiveViewNativeMacros
 
 let testMacros: [String: Macro.Type] = [
     "Registries": RegistriesMacro.self,
+    "LiveView": LiveViewMacro.self
 ]
 
 final class LiveViewNativeMacrosTests: XCTestCase {
@@ -37,4 +38,61 @@ final class LiveViewNativeMacrosTests: XCTestCase {
             macros: testMacros
         )
     }
+    
+    func testLiveViewMacro() {
+        assertMacroExpansion(
+            """
+            #LiveView(.localhost, configuration: .init(), addons: [AVKitRegistry<EmptyRegistry>.self])
+            """,
+            expandedSource: """
+            { () -> AnyView in
+                enum __macro_local_8RegistryfMu_: AggregateRegistry {
+                    typealias Registries = AVKitRegistry<Self>
+                }
+            
+                return AnyView(LiveView<__macro_local_8RegistryfMu_>(.localhost, configuration: .init()))
+            }()
+            """,
+            macros: testMacros
+        )
+        assertMacroExpansion(
+            """
+            #LiveView(
+                .automatic(development: .localhost(port: 5000), production: .custom(URL(string: "example.com")!)),
+                addons: [
+                    AVKitRegistry<EmptyRegistry>.self,
+                    ChartsRegistry<EmptyRegistry>.self
+                ]
+            )
+            """,
+            expandedSource: """
+            { () -> AnyView in
+                enum __macro_local_8RegistryfMu_: AggregateRegistry {
+                    typealias Registries = _MultiRegistry<
+                            AVKitRegistry<Self>,
+                            ChartsRegistry<Self>>
+                }
+            
+                return AnyView(LiveView<__macro_local_8RegistryfMu_>(
+                .automatic(development: .localhost(port: 5000), production: .custom(URL(string: "example.com")!))))
+            }()
+            """,
+            macros: testMacros
+        )
+        assertMacroExpansion(
+            """
+            #LiveView(.localhost, configuration: .init(), addons: [AVKitRegistry<_>.self, ChartsRegistry<Self>.self, PhotoKitRegistry<_>.self])
+            """,
+            expandedSource: """
+            { () -> AnyView in
+                enum __macro_local_8RegistryfMu_: AggregateRegistry {
+                    typealias Registries = _MultiRegistry<AVKitRegistry<Self>, _MultiRegistry<ChartsRegistry<Self>, PhotoKitRegistry<Self>>>
+                }
+            
+                return AnyView(LiveView<__macro_local_8RegistryfMu_>(.localhost, configuration: .init()))
+            }()
+            """,
+            macros: testMacros
+        )
+    }
 }