Generize MemberMacro protocol

Author: DougGregor

Sources/_SwiftSyntaxMacros/MacroProtocols/MemberMacro.swift

@@ -23,10 +23,13 @@ public protocol MemberMacro: AttachedMacro {
   ///
   /// - Returns: the set of member declarations introduced by this macro, which
   /// are nested inside the `attachedTo` declaration.
-  static func expansion(
+  static func expansion<
+    Declaration: DeclGroupSyntax,
+    Context: MacroExpansionContext
+  >(
     of node: AttributeSyntax,
-    attachedTo declaration: DeclSyntax,
-    in context: any MacroExpansionContext
+    attachedTo declaration: Declaration,
+    in context: Context
   ) throws -> [DeclSyntax]
 }
 

Sources/_SwiftSyntaxMacros/MacroSystem.swift

@@ -401,7 +401,7 @@ extension MacroApplication {
         try newMembers.append(
           contentsOf: memberMacro.expansion(
             of: attribute,
-            attachedTo: DeclSyntax(decl),
+            attachedTo: decl,
             in: context
           )
         )
@@ -495,9 +495,9 @@ extension MacroApplication {
 extension SyntaxProtocol {
   /// Expand all uses of the given set of macros within this syntax
   /// node.
-  public func expand(
+  public func expand<Context: MacroExpansionContext>(
     macros: [String: Macro.Type],
-    in context: any MacroExpansionContext
+    in context: Context
   ) -> Syntax {
     // Build the macro system.
     var system = MacroSystem()

Tests/SwiftSyntaxMacrosTest/MacroSystemTests.swift

@@ -440,10 +440,13 @@ public struct AddCompletionHandler: PeerMacro {
 }
 
 public struct AddBackingStorage: MemberMacro {
-  public static func expansion(
+  public static func expansion<
+    Declaration: DeclGroupSyntax,
+    Context: MacroExpansionContext
+  >(
     of node: AttributeSyntax,
-    attachedTo decl: DeclSyntax,
-    in context: any MacroExpansionContext
+    attachedTo decl: Declaration,
+    in context: Context
   )
     throws -> [DeclSyntax]
   {
@@ -527,10 +530,13 @@ public struct WrapStoredProperties: MemberAttributeMacro {
 struct CustomTypeWrapperMacro {}
 
 extension CustomTypeWrapperMacro: MemberMacro {
-  static func expansion(
+  static func expansion<
+    Declaration: DeclGroupSyntax,
+    Context: MacroExpansionContext
+  >(
     of node: AttributeSyntax,
-    attachedTo declaration: DeclSyntax,
-    in context: any MacroExpansionContext
+    attachedTo declaration: Declaration,
+    in context: Context
   ) throws -> [DeclSyntax] {
     return [
       """