[Macros] Pass the extended type syntax for extension macros to

`expandAttachedMacro`.

Author: hborla

Sources/SwiftCompilerPluginMessageHandling/CompilerPluginMessageHandler.swift

@@ -122,14 +122,15 @@ extension CompilerPluginMessageHandler {
         expandingSyntax: expandingSyntax
       )
 
-    case .expandAttachedMacro(let macro, let macroRole, let discriminator, let attributeSyntax, let declSyntax, let parentDeclSyntax):
+    case .expandAttachedMacro(let macro, let macroRole, let discriminator, let attributeSyntax, let declSyntax, let parentDeclSyntax, let extendedTypeSyntax):
       try expandAttachedMacro(
         macro: macro,
         macroRole: macroRole,
         discriminator: discriminator,
         attributeSyntax: attributeSyntax,
         declSyntax: declSyntax,
-        parentDeclSyntax: parentDeclSyntax
+        parentDeclSyntax: parentDeclSyntax,
+        extendedTypeSyntax: extendedTypeSyntax
       )
 
     case .loadPluginLibrary(let libraryPath, let moduleName):

Sources/SwiftCompilerPluginMessageHandling/Macros.swift

@@ -86,7 +86,8 @@ extension CompilerPluginMessageHandler {
     discriminator: String,
     attributeSyntax: PluginMessage.Syntax,
     declSyntax: PluginMessage.Syntax,
-    parentDeclSyntax: PluginMessage.Syntax?
+    parentDeclSyntax: PluginMessage.Syntax?,
+    extendedTypeSyntax: PluginMessage.Syntax?
   ) throws {
     let sourceManager = SourceManager()
     let context = PluginMacroExpansionContext(
@@ -100,6 +101,9 @@ extension CompilerPluginMessageHandler {
     ).cast(AttributeSyntax.self)
     let declarationNode = sourceManager.add(declSyntax).cast(DeclSyntax.self)
     let parentDeclNode = parentDeclSyntax.map { sourceManager.add($0).cast(DeclSyntax.self) }
+    let extendedType = extendedTypeSyntax.map {
+      sourceManager.add($0).cast(TypeSyntax.self)
+    }
 
     // TODO: Make this a 'String?' and remove non-'hasExpandMacroResult' branches.
     let expandedSources: [String]?
@@ -115,6 +119,7 @@ extension CompilerPluginMessageHandler {
         attributeNode: attributeNode,
         declarationNode: declarationNode,
         parentDeclNode: parentDeclNode,
+        extendedType: extendedType,
         in: context
       )
       if let expansions, hostCapability.hasExpandMacroResult {

Sources/SwiftCompilerPluginMessageHandling/PluginMessages.swift

@@ -34,7 +34,8 @@ internal enum HostToPluginMessage: Codable {
     discriminator: String,
     attributeSyntax: PluginMessage.Syntax,
     declSyntax: PluginMessage.Syntax,
-    parentDeclSyntax: PluginMessage.Syntax?
+    parentDeclSyntax: PluginMessage.Syntax?,
+    extendedTypeSyntax: PluginMessage.Syntax?
   )
 
   /// Optionally implemented message to load a dynamic link library.

Sources/SwiftSyntaxMacroExpansion/MacroExpansion.swift

@@ -47,6 +47,7 @@ private enum MacroExpansionError: Error, CustomStringConvertible {
   case parentDeclGroupNil
   case declarationNotDeclGroup
   case declarationNotIdentified
+  case noExtendedTypeSyntax
   case noFreestandingMacroRoles(Macro.Type)
 
   var description: String {
@@ -63,6 +64,9 @@ private enum MacroExpansionError: Error, CustomStringConvertible {
     case .declarationNotIdentified:
       return "declaration is not a 'Identified' syntax"
 
+    case .noExtendedTypeSyntax:
+      return "no extended type for extension macro"
+
     case .noFreestandingMacroRoles(let type):
       return "macro implementation type '\(type)' does not conform to any freestanding macro protocol"
 
@@ -180,6 +184,7 @@ public func expandAttachedMacroWithoutCollapsing<Context: MacroExpansionContext>
   attributeNode: AttributeSyntax,
   declarationNode: DeclSyntax,
   parentDeclNode: DeclSyntax?,
+  extendedType: TypeSyntax?,
   in context: Context
 ) -> [String]? {
   do {
@@ -302,13 +307,10 @@ public func expandAttachedMacroWithoutCollapsing<Context: MacroExpansionContext>
         // Compiler error: type mismatch.
         throw MacroExpansionError.declarationNotDeclGroup
       }
-      guard let identified = declarationNode.asProtocol(IdentifiedDeclSyntax.self)
-      else {
-        // Compiler error: type mismatch.
-        throw MacroExpansionError.declarationNotIdentified
-      }
 
-      let type: TypeSyntax = "\(identified.identifier)"
+      guard let extendedType = extendedType else {
+        throw MacroExpansionError.noExtendedTypeSyntax
+      }
 
       // Local function to expand a extension macro once we've opened up
       // the existential.
@@ -318,7 +320,7 @@ public func expandAttachedMacroWithoutCollapsing<Context: MacroExpansionContext>
         return try attachedMacro.expansion(
           of: attributeNode,
           attachedTo: node,
-          providingExtensionsOf: type,
+          providingExtensionsOf: extendedType,
           in: context
         )
       }
@@ -361,6 +363,7 @@ public func expandAttachedMacro<Context: MacroExpansionContext>(
   attributeNode: AttributeSyntax,
   declarationNode: DeclSyntax,
   parentDeclNode: DeclSyntax?,
+  extendedType: TypeSyntax?,
   in context: Context
 ) -> String? {
   let expandedSources = expandAttachedMacroWithoutCollapsing(
@@ -369,6 +372,7 @@ public func expandAttachedMacro<Context: MacroExpansionContext>(
     attributeNode: attributeNode,
     declarationNode: declarationNode,
     parentDeclNode: parentDeclNode,
+    extendedType: extendedType,
     in: context
   )
   return expandedSources.map {