[Macros] Add a test that invokes macro expansion through the conformance

checker while type checking a freestanding macro argument in the same scope.

(cherry picked from commit f9f63e3)

Author: hborla

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1603,3 +1603,26 @@ extension SelfAlwaysEqualOperator: MemberMacro {
     ]
   }
 }
+
+public struct InitializableMacro: ConformanceMacro, MemberMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingConformancesOf decl: some DeclGroupSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)] {
+    return [("Initializable", nil)]
+  }
+
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingMembersOf decl: some DeclGroupSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    let requirement: DeclSyntax =
+      """
+      init(value: Int) {}
+      """
+
+    return [requirement]
+  }
+}

test/Macros/top_level_freestanding.swift

@@ -104,3 +104,24 @@ func testGlobalVariable() {
 }
 
 #endif
+
+
+@freestanding(declaration)
+macro Empty<T>(_ closure: () -> T) = #externalMacro(module: "MacroDefinition", type: "EmptyDeclarationMacro")
+
+#Empty {
+  S(a: 10, b: 10)
+}
+
+@attached(conformance)
+@attached(member, names: named(init))
+macro Initializable() = #externalMacro(module: "MacroDefinition", type: "InitializableMacro")
+
+protocol Initializable {
+  init(value: Int)
+}
+
+@Initializable
+struct S {
+  init(a: Int, b: Int) {}
+}