[Concurrency] Check the outermost parent source file when diagnosing

Sendable conformances outside the defining source file.

This allows macros to add a Sendable conformance when the macro is applied
in the same source file as the primary declaration.

Author: hborla

lib/Sema/TypeCheckConcurrency.cpp

@@ -5104,8 +5104,9 @@ bool swift::checkSendableConformance(
   auto conformanceDecl = conformanceDC->getAsDecl();
   auto behavior = SendableCheckContext(conformanceDC, check)
       .defaultDiagnosticBehavior();
-  if (conformanceDC->getParentSourceFile() &&
-      conformanceDC->getParentSourceFile() != nominal->getParentSourceFile()) {
+  if (conformanceDC->getOutermostParentSourceFile() &&
+      conformanceDC->getOutermostParentSourceFile() !=
+      nominal->getOutermostParentSourceFile()) {
     conformanceDecl->diagnose(diag::concurrent_value_outside_source_file,
                               nominal)
       .limitBehavior(behavior);

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -2057,6 +2057,31 @@ extension RequiredDefaultInitMacro: MemberMacro {
   }
 }
 
+public struct SendableMacro: ExtensionMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    attachedTo decl: some DeclGroupSyntax,
+    providingExtensionsOf type: some TypeSyntaxProtocol,
+    conformingTo protocols: [TypeSyntax],
+    in context: some MacroExpansionContext
+  ) throws -> [ExtensionDeclSyntax] {
+    if protocols.isEmpty {
+      return []
+    }
+
+    let decl: DeclSyntax =
+      """
+      extension \(type.trimmed): Sendable {
+      }
+
+      """
+
+    return [
+      decl.cast(ExtensionDeclSyntax.self)
+    ]
+  }
+}
+
 public struct FakeCodeItemMacro: DeclarationMacro, PeerMacro {
   public static func expansion(
     of node: some FreestandingMacroExpansionSyntax,

test/Macros/macro_expand_extensions.swift

@@ -244,3 +244,15 @@ func testStringFoo(s: String) {
   "Test".printFoo()
   s.printFoo()
 }
+
+@attached(extension, conformances: Sendable)
+macro AddSendable() = #externalMacro(module: "MacroDefinition", type: "SendableMacro")
+
+@AddSendable
+final class SendableClass {
+}
+
+// expected-warning@+2 {{non-final class 'InvalidSendableClass' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+@AddSendable
+class InvalidSendableClass {
+}