From 6c9fb2428f651666cb96e3cd276637855432516e Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Tue, 9 Feb 2016 04:47:58 +0000
Subject: [PATCH] Use std::forward to make ErrorOr<T> constructible from a
 value that has a user-defined conversion to T. No functionality change
 intended.

llvm-svn: 260196
---
 include/llvm/Support/ErrorOr.h    | 22 +++++-----------
 unittests/Support/ErrorOrTest.cpp | 42 ++++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/include/llvm/Support/ErrorOr.h b/include/llvm/Support/ErrorOr.h
index 7fe1d5a16e8..877f4063cd2 100644
--- a/include/llvm/Support/ErrorOr.h
+++ b/include/llvm/Support/ErrorOr.h
@@ -23,20 +23,6 @@
 #include <type_traits>
 
 namespace llvm {
-template<class T, class V>
-typename std::enable_if< std::is_constructible<T, V>::value
-                       , typename std::remove_reference<V>::type>::type &&
- moveIfMoveConstructible(V &Val) {
-  return std::move(Val);
-}
-
-template<class T, class V>
-typename std::enable_if< !std::is_constructible<T, V>::value
-                       , typename std::remove_reference<V>::type>::type &
-moveIfMoveConstructible(V &Val) {
-  return Val;
-}
-
 /// \brief Stores a reference that can be changed.
 template <typename T>
 class ReferenceStorage {
@@ -107,8 +93,12 @@ public:
     new (getErrorStorage()) std::error_code(EC);
   }
 
-  ErrorOr(T Val) : HasError(false) {
-    new (getStorage()) storage_type(moveIfMoveConstructible<storage_type>(Val));
+  template <class OtherT>
+  ErrorOr(OtherT &&Val,
+          typename std::enable_if<std::is_convertible<OtherT, T>::value>::type
+              * = nullptr)
+      : HasError(false) {
+    new (getStorage()) storage_type(std::forward<OtherT>(Val));
   }
 
   ErrorOr(const ErrorOr &Other) {
diff --git a/unittests/Support/ErrorOrTest.cpp b/unittests/Support/ErrorOrTest.cpp
index 73d0e3f2bb7..87dcab7b181 100644
--- a/unittests/Support/ErrorOrTest.cpp
+++ b/unittests/Support/ErrorOrTest.cpp
@@ -16,7 +16,7 @@ using namespace llvm;
 
 namespace {
 
-ErrorOr<int> t1() {return 1;}
+ErrorOr<int> t1() { return 1; }
 ErrorOr<int> t2() { return errc::invalid_argument; }
 
 TEST(ErrorOr, SimpleValue) {
@@ -71,6 +71,46 @@ TEST(ErrorOr, Comparison) {
   EXPECT_EQ(x, errc::no_such_file_or_directory);
 }
 
+TEST(ErrorOr, ImplicitConversion) {
+  ErrorOr<std::string> x("string literal");
+  EXPECT_TRUE(!!x);
+}
+
+TEST(ErrorOr, ImplicitConversionCausesMove) {
+  struct Source {};
+  struct Destination {
+    Destination(const Source&) {}
+    Destination(Source&&) = delete;
+  };
+  Source s;
+  ErrorOr<Destination> x = s;
+  EXPECT_TRUE(!!x);
+}
+
+TEST(ErrorOr, ImplicitConversionNoAmbiguity) {
+  struct CastsToErrorCode {
+    CastsToErrorCode() = default;
+    CastsToErrorCode(std::error_code) {}
+    operator std::error_code() { return errc::invalid_argument; }
+  } casts_to_error_code;
+  ErrorOr<CastsToErrorCode> x1(casts_to_error_code);
+  ErrorOr<CastsToErrorCode> x2 = casts_to_error_code;
+  ErrorOr<CastsToErrorCode> x3 = {casts_to_error_code};
+  ErrorOr<CastsToErrorCode> x4{casts_to_error_code};
+  ErrorOr<CastsToErrorCode> x5(errc::no_such_file_or_directory);
+  ErrorOr<CastsToErrorCode> x6 = errc::no_such_file_or_directory;
+  ErrorOr<CastsToErrorCode> x7 = {errc::no_such_file_or_directory};
+  ErrorOr<CastsToErrorCode> x8{errc::no_such_file_or_directory};
+  EXPECT_TRUE(!!x1);
+  EXPECT_TRUE(!!x2);
+  EXPECT_TRUE(!!x3);
+  EXPECT_TRUE(!!x4);
+  EXPECT_FALSE(x5);
+  EXPECT_FALSE(x6);
+  EXPECT_FALSE(x7);
+  EXPECT_FALSE(x8);
+}
+
 // ErrorOr<int*> x(nullptr);
 // ErrorOr<std::unique_ptr<int>> y = x; // invalid conversion
 static_assert(