From dc6b70d7363dfd4e0ef7f5b3949605b92760ec0d Mon Sep 17 00:00:00 2001
From: Jordan Rose <jordan_rose@apple.com>
Date: Fri, 7 Oct 2016 21:07:22 -0700
Subject: [PATCH] Disallow ArrayRef assignment from temporaries.

Without this, the following statements will create ArrayRefs that refer to
temporary storage that goes out of scope by the end of the line:

  someArrayRef = getSingleElement();
  someArrayRef = {elem1, elem2};

Note that the constructor still has this problem:

  ArrayRef<Element> someArrayRef = getSingleElement();
  ArrayRef<Element> someArrayRef = {elem1, elem2};

but that's a little harder to get rid of because we want to be able to use
this in calls:

  takesArrayRef(getSingleElement());
  takesArrayRef({elem1, elem2});

Part of rdar://problem/16375365
---
 include/llvm/ADT/ArrayRef.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/llvm/ADT/ArrayRef.h b/include/llvm/ADT/ArrayRef.h
index bfe851485f3..41a54c390bc 100644
--- a/include/llvm/ADT/ArrayRef.h
+++ b/include/llvm/ADT/ArrayRef.h
@@ -203,6 +203,22 @@ namespace llvm {
       return Data[Index];
     }
 
+    /// Disallow accidental assignment from a temporary.
+    ///
+    /// The declaration here is extra complicated so that "arrayRef = {}"
+    /// continues to select the move assignment operator.
+    template <typename U>
+    typename std::enable_if<std::is_same<U, T>::value, ArrayRef<T>>::type &
+    operator=(U &&Temporary) = delete;
+
+    /// Disallow accidental assignment from a temporary.
+    ///
+    /// The declaration here is extra complicated so that "arrayRef = {}"
+    /// continues to select the move assignment operator.
+    template <typename U>
+    typename std::enable_if<std::is_same<U, T>::value, ArrayRef<T>>::type &
+    operator=(std::initializer_list<U>) = delete;
+
     /// @}
     /// @name Expensive Operations
     /// @{