Fix folly::Range compile error when using non-POD value type, c++17, and libc++

Summary:
When using clang, libc++, and c++17, merely mentioning a Range with a non-pod
value-type will give a compile error due to a static assert while attemption to
instantiate a basic_string_view. Using a StrictConjunction seems to fix this
issue.

Reviewed By: yfeldblum

Differential Revision: D10472408

fbshipit-source-id: 28d50d0a99994049bfcd9ac29168fb2f1d1c5867

folly/Range.h

@@ -543,9 +543,10 @@ class Range {
   template <
       typename Tgt,
       std::enable_if_t<
-          std::is_same<Tgt, StringViewType>::value &&
-              std::is_constructible<StringViewType, Iter const&, size_type>::
-                  value,
+          StrictConjunction<
+              std::is_same<Tgt, StringViewType>,
+              std::is_constructible<StringViewType, Iter const&, size_type>>::
+              value,
           int> = 0>
   constexpr operator Tgt() const noexcept(
       std::is_nothrow_constructible<Tgt, Iter const&, size_type>::value) {

folly/test/RangeTest.cpp

@@ -1620,4 +1620,16 @@ TEST(StringPiece, StringViewConversion) {
   TrickierTarget tt3(deqRange);
   EXPECT_EQ(tt3.which, 1);
 }
+
+namespace {
+
+// Range with non-pod value type should not cause compile errors.
+class NonPOD {
+ public:
+  NonPOD() {}
+};
+void test_func(Range<const NonPOD*>) {}
+
+} // anonymous namespace
+
 #endif