[ADT] Add SmallVector::assign overload for ArrayRef (llvm#164680)

We already have a matching constructor from ArrayRef, so add support for
assigning from ArrayRef as well.

Author: kuhar

llvm/include/llvm/ADT/SmallVector.h

@@ -734,6 +734,12 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> {
 
   void assign(const SmallVectorImpl &RHS) { assign(RHS.begin(), RHS.end()); }
 
+  template <typename U,
+            typename = std::enable_if_t<std::is_convertible_v<U, T>>>
+  void assign(ArrayRef<U> AR) {
+    assign(AR.begin(), AR.end());
+  }
+
   iterator erase(const_iterator CI) {
     // Just cast away constness because this is a non-const member function.
     iterator I = const_cast<iterator>(CI);
@@ -1228,7 +1234,7 @@ class LLVM_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
   }
 
   template <typename U,
-            typename = std::enable_if_t<std::is_convertible<U, T>::value>>
+            typename = std::enable_if_t<std::is_convertible_v<U, T>>>
   explicit SmallVector(ArrayRef<U> A) : SmallVectorImpl<T>(N) {
     this->append(A.begin(), A.end());
   }

llvm/unittests/ADT/SmallVectorTest.cpp

@@ -599,6 +599,15 @@ TYPED_TEST(SmallVectorTest, AssignSmallVector) {
   assertValuesInOrder(V, 2u, 7, 7);
 }
 
+TYPED_TEST(SmallVectorTest, AssignArrayRef) {
+  SCOPED_TRACE("AssignArrayRef");
+  auto &V = this->theVector;
+  Constructable Other[] = {7, 8, 9};
+  V.push_back(Constructable(1));
+  V.assign(ArrayRef(Other));
+  assertValuesInOrder(V, 3u, 7, 8, 9);
+}
+
 // Move-assign test
 TYPED_TEST(SmallVectorTest, MoveAssignTest) {
   SCOPED_TRACE("MoveAssignTest");