Index: include/llvm/Support/Error.h
===================================================================
--- include/llvm/Support/Error.h
+++ include/llvm/Support/Error.h
@@ -952,6 +952,7 @@
 
 /// Write all error messages (if any) in E to a string. The newline character
 /// is used to separate error messages.
+/// DEPRECATED: prefer llvm::to_string(E) from ScopedPrinter.h
 inline std::string toString(Error E) {
   SmallVector<std::string, 2> Errors;
   handleAllErrors(std::move(E), [&Errors](const ErrorInfoBase &EI) {
@@ -971,6 +972,13 @@
   handleAllErrors(std::move(Err), [](const ErrorInfoBase &) {});
 }
 
+/// Sending an rvalue error to a raw_ostream prints its message and consumes it.
+inline raw_ostream &operator<<(raw_ostream &OS, Error &&E) {
+  OS << static_cast<const Error &>(E);
+  consumeError(std::move(E));
+  return OS;
+}
+
 /// Helper for converting an Error to a bool.
 ///
 /// This method returns true if Err is in an error state, or false if it is
Index: include/llvm/Support/FormatVariadicDetails.h
===================================================================
--- include/llvm/Support/FormatVariadicDetails.h
+++ include/llvm/Support/FormatVariadicDetails.h
@@ -46,7 +46,9 @@
   explicit stream_operator_format_adapter(T &&Item)
       : Item(std::forward<T>(Item)) {}
 
-  void format(llvm::raw_ostream &S, StringRef Options) override { S << Item; }
+  void format(llvm::raw_ostream &S, StringRef Options) override {
+    S << std::forward<T>(Item);
+  }
 };
 
 template <typename T> class missing_format_adapter;
Index: include/llvm/Support/ScopedPrinter.h
===================================================================
--- include/llvm/Support/ScopedPrinter.h
+++ include/llvm/Support/ScopedPrinter.h
@@ -59,10 +59,10 @@
 raw_ostream &operator<<(raw_ostream &OS, const HexNumber &Value);
 const std::string to_hexString(uint64_t Value, bool UpperCase = true);
 
-template <class T> const std::string to_string(const T &Value) {
+template <class T> const std::string to_string(T &&Value) {
   std::string number;
   llvm::raw_string_ostream stream(number);
-  stream << Value;
+  stream << std::forward<T>(Value);
   return stream.str();
 }
 
Index: unittests/Support/ErrorTest.cpp
===================================================================
--- unittests/Support/ErrorTest.cpp
+++ unittests/Support/ErrorTest.cpp
@@ -12,6 +12,7 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Testing/Support/Error.h"
 #include "gtest/gtest-spi.h"
 #include "gtest/gtest.h"
@@ -700,20 +701,28 @@
 // Test that error messages work.
 TEST(Error, ErrorMessage) {
   EXPECT_EQ(toString(Error::success()).compare(""), 0);
+  EXPECT_EQ(to_string(Error::success()), "success");
 
-  Error E1 = make_error<CustomError>(0);
-  EXPECT_EQ(toString(std::move(E1)).compare("CustomError {0}"), 0);
+  Error E1A = make_error<CustomError>(0), E1B = make_error<CustomError>(0);
+  EXPECT_EQ(to_string(E1A), "CustomError {0}");
+  EXPECT_EQ(toString(std::move(E1A)).compare("CustomError {0}"), 0);
+  EXPECT_EQ(to_string(std::move(E1B)).compare("CustomError {0}"), 0);
 
   Error E2 = make_error<CustomError>(0);
   handleAllErrors(std::move(E2), [](const CustomError &CE) {
     EXPECT_EQ(CE.message().compare("CustomError {0}"), 0);
   });
 
-  Error E3 = joinErrors(make_error<CustomError>(0), make_error<CustomError>(1));
-  EXPECT_EQ(toString(std::move(E3))
+  Error E3A =
+            joinErrors(make_error<CustomError>(0), make_error<CustomError>(1)),
+        E3B =
+            joinErrors(make_error<CustomError>(0), make_error<CustomError>(1));
+  EXPECT_EQ(toString(std::move(E3A))
                 .compare("CustomError {0}\n"
                          "CustomError {1}"),
             0);
+  EXPECT_EQ(to_string(std::move(E3B)),
+            "Multiple errors:\nCustomError {0}\nCustomError {1}\n");
 }
 
 TEST(Error, Stream) {
Index: unittests/Support/FormatVariadicTest.cpp
===================================================================
--- unittests/Support/FormatVariadicTest.cpp
+++ unittests/Support/FormatVariadicTest.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FormatAdapters.h"
 #include "gtest/gtest.h"
 
@@ -680,3 +681,11 @@
   adl::X X;
   EXPECT_EQ("X", formatv("{0}", X).str());
 }
+
+TEST(FormatVariadicTest, FormatError) {
+  auto E1 = make_error<StringError>("X", inconvertibleErrorCode());
+  EXPECT_EQ("X", formatv("{0}", E1).str());
+  EXPECT_TRUE(E1.isA<StringError>()); // not consumed
+  EXPECT_EQ("X", formatv("{0}", std::move(E1)).str());
+  EXPECT_FALSE(E1.isA<StringError>()); // consumed
+}