Deserialization: ignore search paths pointing into the SDK. rdar://84125071

Author: nkcsgexi

lib/Serialization/ModuleFile.cpp

@@ -165,10 +165,15 @@ Status ModuleFile::associateWithFileContext(FileUnit *file, SourceLoc diagLoc,
     return error(status);
   }
 
-  for (const auto &searchPath : Core->SearchPaths) {
-    ctx.addSearchPath(
+  StringRef SDKPath = ctx.SearchPathOpts.SDKPath;
+  if (SDKPath.empty() ||
+      !Core->ModuleInputBuffer->getBufferIdentifier().startswith(SDKPath)) {
+    for (const auto &searchPath : Core->SearchPaths) {
+      ctx.addSearchPath(
         ctx.SearchPathOpts.SearchPathRemapper.remapPath(searchPath.Path),
-        searchPath.IsFramework, searchPath.IsSystem);
+        searchPath.IsFramework,
+        searchPath.IsSystem);
+    }
   }
 
   auto clangImporter = static_cast<ClangImporter *>(ctx.getClangModuleLoader());

test/Serialization/search-paths-sdk.swift

@@ -0,0 +1,16 @@
+// REQUIRES: VENDOR=apple
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/mock-sdk/usr/lib/swift/SystemLibrary.swiftmodule)
+// RUN: %empty-directory(%t/secret)
+
+// RUN: %target-swift-frontend -emit-module %S/../Inputs/empty.swift -o %t/secret/SecretLibrary.swiftmodule
+// RUN: %target-swift-frontend -emit-module %S/../Inputs/empty.swift -o %t/mock-sdk/usr/lib/swift/SystemLibrary.swiftmodule/%target-swiftmodule-name -module-name SystemLibrary -I %t/secret -serialize-debugging-options
+
+// We pick up search paths from normal imports...
+// RUN: %target-swift-frontend -typecheck %s -I %t/mock-sdk/usr/lib/swift/
+
+// ...but not from content in the SDK.
+// RUN: %target-swift-frontend -typecheck %s -sdk %t/mock-sdk -verify -show-diagnostics-after-fatal
+
+import SystemLibrary
+import SecretLibrary // expected-error {{no such module 'SecretLibrary'}}