[Test] Ensure that freestanding macros in unprocessed #ifs aren't expanded.

Tracked by rdar://110083415.

Author: DougGregor

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1505,3 +1505,29 @@ public struct SingleMemberMacro: MemberMacro {
     ]
   }
 }
+
+public struct UseIdentifierMacro: DeclarationMacro {
+  public static func expansion(
+    of node: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    guard let argument = node.argumentList.first?.expression.as(StringLiteralExprSyntax.self) else {
+      fatalError("boom")
+    }
+    return [
+      """
+      func \(context.makeUniqueName("name"))() {
+        _ = \(raw: argument.segments.first!)
+      }
+      """,
+      """
+      struct Foo {
+        var \(context.makeUniqueName("name")): Int {
+          _ = \(raw: argument.segments.first!)
+          return 0
+        }
+      }
+      """
+    ]
+  }
+}

test/Macros/macro_expand_primary.swift

@@ -85,3 +85,13 @@ final class Dog: Observable {
 func test() {
   observeDog()
 }
+
+
+@freestanding(declaration, names: named(Foo)) macro useIdentifier(_ value: String) = #externalMacro(module: "MacroDefinition", type: "UseIdentifierMacro")
+
+#if false
+#useIdentifier("totallyNotDefined")
+#else
+let hello = "Hello"
+#useIdentifier("hello")
+#endif