From d21a535bf6201163d1cd4a14ba77a07a94535fa7 Mon Sep 17 00:00:00 2001
From: Lang Hames <lhames@gmail.com>
Date: Thu, 24 Mar 2016 02:00:10 +0000
Subject: [PATCH] [Support] Add conversions between Expected<T> and ErrorOr<T>.

More utilities to help with std::error_code -> Error transitions.

llvm-svn: 264238
---
 llvm/include/llvm/Support/Error.h    | 16 ++++++++++++++++
 llvm/unittests/Support/ErrorTest.cpp | 25 ++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Support/Error.h b/llvm/include/llvm/Support/Error.h
index f1eccf8..1432cb1 100644
--- a/llvm/include/llvm/Support/Error.h
+++ b/llvm/include/llvm/Support/Error.h
@@ -753,6 +753,22 @@ inline std::error_code errorToErrorCode(Error Err) {
   return EC;
 }
 
+/// Convert an ErrorOr<T> to an Expected<T>.
+template <typename T>
+Expected<T> errorOrToExpected(ErrorOr<T> &&EO) {
+  if (auto EC = EO.getError())
+    return errorCodeToError(EC);
+  return std::move(*EO);
+}
+
+/// Convert an Expected<T> to an ErrorOr<T>.
+template <typename T>
+ErrorOr<T> expectedToErrorOr(Expected<T> &&E) {
+  if (auto Err = E.takeError())
+    return errorToErrorCode(std::move(Err));
+  return std::move(*E);
+}
+
 /// Helper for check-and-exit error handling.
 ///
 /// For tool use only. NOT FOR USE IN LIBRARY CODE.
diff --git a/llvm/unittests/Support/ErrorTest.cpp b/llvm/unittests/Support/ErrorTest.cpp
index 1807547..fadb00c 100644
--- a/llvm/unittests/Support/ErrorTest.cpp
+++ b/llvm/unittests/Support/ErrorTest.cpp
@@ -416,7 +416,7 @@ TEST(Error, ExpectedCovariance) {
   A2 = Expected<std::unique_ptr<D>>(nullptr);
 }
 
-TEST(Error, ECError) {
+TEST(Error, ErrorCodeConversions) {
   // Round-trip a success value to check that it converts correctly.
   EXPECT_EQ(errorToErrorCode(errorCodeToError(std::error_code())),
             std::error_code())
@@ -427,6 +427,29 @@ TEST(Error, ECError) {
             errc::invalid_argument)
       << "std::error_code error value should round-trip via Error "
          "conversions";
+
+  // Round-trip a success value through ErrorOr/Expected to check that it
+  // converts correctly.
+  {
+    auto Orig = ErrorOr<int>(42);
+    auto RoundTripped =
+      expectedToErrorOr(errorOrToExpected(ErrorOr<int>(42)));
+    EXPECT_EQ(*Orig, *RoundTripped)
+      << "ErrorOr<T> success value should round-trip via Expected<T> "
+         "conversions.";
+  }
+
+  // Round-trip a failure value through ErrorOr/Expected to check that it
+  // converts correctly.
+  {
+    auto Orig = ErrorOr<int>(errc::invalid_argument);
+    auto RoundTripped =
+      expectedToErrorOr(
+          errorOrToExpected(ErrorOr<int>(errc::invalid_argument)));
+    EXPECT_EQ(Orig.getError(), RoundTripped.getError())
+      << "ErrorOr<T> failure value should round-trip via Expected<T> "
+         "conversions.";
+  }
 }
 
 } // end anon namespace
-- 
2.7.4