Index: clang/include/clang/Frontend/ASTUnit.h
===================================================================
--- clang/include/clang/Frontend/ASTUnit.h
+++ clang/include/clang/Frontend/ASTUnit.h
@@ -876,7 +876,6 @@
                     CodeCompleteConsumer &Consumer,
                     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
                     DiagnosticsEngine &Diag, LangOptions &LangOpts,
-                    SourceManager &SourceMgr, FileManager &FileMgr,
                     SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
                     SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers);
 
Index: clang/lib/Frontend/ASTUnit.cpp
===================================================================
--- clang/lib/Frontend/ASTUnit.cpp
+++ clang/lib/Frontend/ASTUnit.cpp
@@ -2132,8 +2132,8 @@
     bool IncludeCodePatterns, bool IncludeBriefComments,
     CodeCompleteConsumer &Consumer,
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-    DiagnosticsEngine &Diag, LangOptions &LangOpts, SourceManager &SourceMgr,
-    FileManager &FileMgr, SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
+    DiagnosticsEngine &Diag, LangOptions &LangOpts,
+    SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
     SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers) {
   if (!Invocation)
     return;
@@ -2211,9 +2211,12 @@
              Language::LLVM_IR &&
          "IR inputs not support here!");
 
-  // Use the source and file managers that we were given.
-  Clang->setFileManager(&FileMgr);
-  Clang->setSourceManager(&SourceMgr);
+  // Initialize file and source managers up front so that the caller can access
+  // them after.
+  Clang->createFileManager(FS);
+  FileMgr = &Clang->getFileManager();
+  Clang->createSourceManager(*FileMgr);
+  SourceMgr = &Clang->getSourceManager();
 
   // Remap files.
   PreprocessorOpts.clearRemappedFiles();
Index: clang/tools/libclang/CIndexCodeCompletion.cpp
===================================================================
--- clang/tools/libclang/CIndexCodeCompletion.cpp
+++ clang/tools/libclang/CIndexCodeCompletion.cpp
@@ -359,8 +359,6 @@
     : CXCodeCompleteResults(), DiagOpts(new DiagnosticOptions),
       Diag(new DiagnosticsEngine(
           IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs), &*DiagOpts)),
-      FileMgr(std::move(FileMgr)),
-      SourceMgr(new SourceManager(*Diag, *this->FileMgr)),
       CodeCompletionAllocator(
           std::make_shared<clang::GlobalCodeCompletionAllocator>()),
       Contexts(CXCompletionContext_Unknown),
@@ -755,14 +753,15 @@
   LibclangInvocationReporter InvocationReporter(
       *CXXIdx, LibclangInvocationReporter::OperationKind::CompletionOperation,
       TU->ParsingOptions, CArgs, CompletionInvocation, unsaved_files);
-  AST->CodeComplete(complete_filename, complete_line, complete_column,
-                    RemappedFiles, (options & CXCodeComplete_IncludeMacros),
-                    (options & CXCodeComplete_IncludeCodePatterns),
-                    IncludeBriefComments, Capture,
-                    CXXIdx->getPCHContainerOperations(), *Results->Diag,
-                    Results->LangOpts, *Results->SourceMgr, *Results->FileMgr,
-                    Results->Diagnostics, Results->TemporaryBuffers);
-
+  AST->CodeComplete(
+      complete_filename, complete_line, complete_column, RemappedFiles,
+      (options & CXCodeComplete_IncludeMacros),
+      (options & CXCodeComplete_IncludeCodePatterns), IncludeBriefComments,
+      Capture, CXXIdx->getPCHContainerOperations(), *Results->Diag,
+      Results->LangOpts, Results->Diagnostics, Results->TemporaryBuffers);
+
+  Results->FileMgr = &AST->getFileManager();
+  Results->SourceMgr = &AST->getSourceManager();
   Results->DiagnosticsWrappers.resize(Results->Diagnostics.size());
 
   // Keep a reference to the allocator used for cached global completions, so