[test] Fix extension macros in test suite

Make sure we're using `providingExtensionsOf` as the extended type,
previously we were just using the unqualified name of the decl.

Author: hamishknight

test/ConstExtraction/Inputs/Macros.swift

@@ -41,10 +41,9 @@ public struct AddExtensionMacro: ExtensionMacro {
     conformingTo protocols: [TypeSyntax],
     in context: some MacroExpansionContext
   ) throws -> [ExtensionDeclSyntax] {
-    let typeName = declaration.declGroupName
     return protocols.map {
       ("""
-      extension \(typeName): \($0) {
+      extension \(type.trimmed): \($0) {
         struct _Extension_\($0): \($0) {
           var nested = 8
         }
@@ -53,8 +52,8 @@ public struct AddExtensionMacro: ExtensionMacro {
       .cast(ExtensionDeclSyntax.self)
     } + [
     ("""
-    extension \(typeName) {
-      static let _extension_\(typeName) = 3
+    extension \(type.trimmed) {
+      static let _extension_\(declaration.declGroupName) = 3
     }
     """ as DeclSyntax).cast(ExtensionDeclSyntax.self)
     ]

test/Reflection/Inputs/Macros.swift

@@ -40,10 +40,9 @@ public struct AddExtensionMacro: ExtensionMacro {
     conformingTo protocols: [TypeSyntax],
     in context: some MacroExpansionContext
   ) throws -> [ExtensionDeclSyntax] {
-    let typeName = declaration.declGroupName
     return protocols.map {
       ("""
-      extension \(typeName): \($0) {
+      extension \(type.trimmed): \($0) {
         struct _Extension_\($0): \($0) {}
       }
       """ as DeclSyntax)
@@ -66,12 +65,3 @@ extension DeclSyntaxProtocol {
         fatalError("Not implemented")
     }
 }
-
-extension DeclGroupSyntax {
-    var declGroupName: TokenSyntax {
-        if let structDecl = self.as(StructDeclSyntax.self) {
-            return structDecl.name.trimmed
-        }
-        fatalError("Not implemented")
-    }
-}