Index: cfe/trunk/include/clang/Basic/DiagnosticError.h
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticError.h
+++ cfe/trunk/include/clang/Basic/DiagnosticError.h
@@ -0,0 +1,61 @@
+//===--- DiagnosticError.h - Diagnostic payload for llvm::Error -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_DIAGNOSTIC_ERROR_H
+#define LLVM_CLANG_BASIC_DIAGNOSTIC_ERROR_H
+
+#include "clang/Basic/PartialDiagnostic.h"
+#include "llvm/Support/Error.h"
+
+namespace clang {
+
+/// \brief Carries a Clang diagnostic in an llvm::Error.
+///
+/// Users should emit the stored diagnostic using the DiagnosticsEngine.
+class DiagnosticError : public llvm::ErrorInfo<DiagnosticError> {
+public:
+  DiagnosticError(PartialDiagnosticAt Diag) : Diag(std::move(Diag)) {}
+
+  void log(raw_ostream &OS) const override { OS << "clang diagnostic"; }
+
+  PartialDiagnosticAt &getDiagnostic() { return Diag; }
+  const PartialDiagnosticAt &getDiagnostic() const { return Diag; }
+
+  /// Creates a new \c DiagnosticError that contains the given diagnostic at
+  /// the given location.
+  static llvm::Error create(SourceLocation Loc, PartialDiagnostic Diag) {
+    return llvm::make_error<DiagnosticError>(
+        PartialDiagnosticAt(Loc, std::move(Diag)));
+  }
+
+  /// Extracts and returns the diagnostic payload from the given \c Error if
+  /// the error is a \c DiagnosticError. Returns none if the given error is not
+  /// a \c DiagnosticError.
+  static Optional<PartialDiagnosticAt> take(llvm::Error &Err) {
+    Optional<PartialDiagnosticAt> Result;
+    Err = llvm::handleErrors(std::move(Err), [&](DiagnosticError &E) {
+      Result = std::move(E.getDiagnostic());
+    });
+    return Result;
+  }
+
+  static char ID;
+
+private:
+  // Users are not expected to use error_code.
+  std::error_code convertToErrorCode() const override {
+    return llvm::inconvertibleErrorCode();
+  }
+
+  PartialDiagnosticAt Diag;
+};
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_BASIC_DIAGNOSTIC_ERROR_H
Index: cfe/trunk/lib/Basic/Diagnostic.cpp
===================================================================
--- cfe/trunk/lib/Basic/Diagnostic.cpp
+++ cfe/trunk/lib/Basic/Diagnostic.cpp
@@ -11,8 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Basic/CharInfo.h"
 #include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/CharInfo.h"
+#include "clang/Basic/DiagnosticError.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/PartialDiagnostic.h"
@@ -1050,3 +1051,5 @@
           llvm::CrashRecoveryContext::isRecoveringFromCrash()) &&
          "A partial is on the lam");
 }
+
+char DiagnosticError::ID;
Index: cfe/trunk/unittests/Basic/DiagnosticTest.cpp
===================================================================
--- cfe/trunk/unittests/Basic/DiagnosticTest.cpp
+++ cfe/trunk/unittests/Basic/DiagnosticTest.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/DiagnosticError.h"
 #include "clang/Basic/DiagnosticIDs.h"
 #include "gtest/gtest.h"
 
@@ -72,4 +73,25 @@
   }
 }
 
+TEST(DiagnosticTest, diagnosticError) {
+  DiagnosticsEngine Diags(new DiagnosticIDs(), new DiagnosticOptions,
+                          new IgnoringDiagConsumer());
+  PartialDiagnostic::StorageAllocator Alloc;
+  llvm::Expected<std::pair<int, int>> Value = DiagnosticError::create(
+      SourceLocation(), PartialDiagnostic(diag::err_cannot_open_file, Alloc)
+                            << "file"
+                            << "error");
+  ASSERT_TRUE(!Value);
+  llvm::Error Err = Value.takeError();
+  Optional<PartialDiagnosticAt> ErrDiag = DiagnosticError::take(Err);
+  llvm::cantFail(std::move(Err));
+  ASSERT_FALSE(!ErrDiag);
+  EXPECT_EQ(ErrDiag->first, SourceLocation());
+  EXPECT_EQ(ErrDiag->second.getDiagID(), diag::err_cannot_open_file);
+
+  Value = std::make_pair(20, 1);
+  ASSERT_FALSE(!Value);
+  EXPECT_EQ(*Value, std::make_pair(20, 1));
+  EXPECT_EQ(Value->first, 20);
+}
 }