Merge pull request #74413 from DougGregor/preconcurrency-import-underlying-6.0

[6.0] Teach "find imports" to equate overlay modules with their underlying modules

Author: DougGregor

lib/AST/Module.cpp

@@ -2667,9 +2667,11 @@ ImportDeclRequest::evaluate(Evaluator &evaluator, const SourceFile *sf,
   auto &ctx = sf->getASTContext();
   auto imports = sf->getImports();
 
+  auto mutModule = const_cast<ModuleDecl *>(module);
   // Look to see if the owning module was directly imported.
   for (const auto &import : imports) {
-    if (import.module.importedModule == module)
+    if (import.module.importedModule
+            ->isSameModuleLookingThroughOverlays(mutModule))
       return import;
   }
 
@@ -2678,7 +2680,8 @@ ImportDeclRequest::evaluate(Evaluator &evaluator, const SourceFile *sf,
   for (const auto &import : imports) {
     auto &importSet = importCache.getImportSet(import.module.importedModule);
     for (const auto &transitive : importSet.getTransitiveImports()) {
-      if (transitive.importedModule == module) {
+      if (transitive.importedModule
+              ->isSameModuleLookingThroughOverlays(mutModule)) {
         return import;
       }
     }

test/Concurrency/predates_concurrency_import_foundation_darwin.swift

@@ -0,0 +1,12 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -swift-version 6 -I %t %s -emit-sil -o /dev/null -verify -parse-as-library
+
+// REQUIRES: OS=macosx
+
+import Foundation
+@preconcurrency import Darwin
+
+func mach_task_self() -> mach_port_t {
+    return mach_task_self_
+}