Add JSValue constructor for std::optional<T> (#6873)

* Add JSValue constructor for std::optional<T>

* Change files

Author: vmoroz

change/react-native-windows-4c6173d5-34ac-4bd7-b040-a5412e7e16fd.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Add JSValue constructor for std::optional<T>",
+  "packageName": "react-native-windows",
+  "email": "vmorozov@microsoft.com",
+  "dependentChangeType": "patch"
+}

vnext/Microsoft.ReactNative.Cxx.UnitTests/JSValueTest.cpp

@@ -304,6 +304,76 @@ TEST_CLASS (JSValueTest) {
     TestCheckEqual(4.2, *value11.TryGetDouble());
   }
 
+  TEST_METHOD(TestJSValueStdOptionalConstructor) {
+    auto value001 = JSValue{std::optional{nullptr}};
+    auto value002 = JSValue{std::optional{JSValueObject{{"prop1", 3}}}};
+    auto value003 = JSValue{std::optional{JSValueObject{}}};
+    auto value004 = JSValue{std::optional{JSValueArray{1, 2}}};
+    auto value005 = JSValue{std::optional{JSValueArray{}}};
+    auto value006 = JSValue{std::optional{"Hello"}};
+    auto value007 = JSValue{std::optional{true}};
+    auto value008 = JSValue{std::optional{false}};
+    auto value009 = JSValue{std::optional{0}};
+    auto value010 = JSValue{std::optional{42}};
+    auto value011 = JSValue{std::optional{4.2}};
+
+    TestCheckEqual(JSValueType::Null, value001.Type());
+    TestCheckEqual(JSValueType::Object, value002.Type());
+    TestCheckEqual(JSValueType::Object, value003.Type());
+    TestCheckEqual(JSValueType::Array, value004.Type());
+    TestCheckEqual(JSValueType::Array, value005.Type());
+    TestCheckEqual(JSValueType::String, value006.Type());
+    TestCheckEqual(JSValueType::Boolean, value007.Type());
+    TestCheckEqual(JSValueType::Boolean, value008.Type());
+    TestCheckEqual(JSValueType::Int64, value009.Type());
+    TestCheckEqual(JSValueType::Int64, value010.Type());
+    TestCheckEqual(JSValueType::Double, value011.Type());
+
+    TestCheck(value001.IsNull());
+    TestCheckEqual(1u, value002.TryGetObject()->size());
+    TestCheckEqual(0u, value003.TryGetObject()->size());
+    TestCheckEqual(2u, value004.TryGetArray()->size());
+    TestCheckEqual(0u, value005.TryGetArray()->size());
+    TestCheckEqual("Hello", *value006.TryGetString());
+    TestCheckEqual(true, *value007.TryGetBoolean());
+    TestCheckEqual(false, *value008.TryGetBoolean());
+    TestCheckEqual(0, *value009.TryGetInt64());
+    TestCheckEqual(42, *value010.TryGetInt64());
+    TestCheckEqual(4.2, *value011.TryGetDouble());
+
+    auto value101 = JSValue{std::nullopt};
+    TestCheckEqual(JSValueType::Null, value101.Type());
+    TestCheck(value101.IsNull());
+
+    auto value201 = JSValue{std::optional<std::nullptr_t>{std::nullopt}};
+    auto value202 = JSValue{std::optional<JSValueObject>{std::nullopt}};
+    auto value203 = JSValue{std::optional<JSValueArray>{std::nullopt}};
+    auto value204 = JSValue{std::optional<const char *>{std::nullopt}};
+    auto value205 = JSValue{std::optional<std::string>{std::nullopt}};
+    auto value206 = JSValue{std::optional<std::string_view>{std::nullopt}};
+    auto value207 = JSValue{std::optional<bool>{std::nullopt}};
+    auto value208 = JSValue{std::optional<int32_t>{std::nullopt}};
+    auto value209 = JSValue{std::optional<int64_t>{std::nullopt}};
+    auto value210 = JSValue{std::optional<uint32_t>{std::nullopt}};
+    auto value211 = JSValue{std::optional<uint64_t>{std::nullopt}};
+    auto value212 = JSValue{std::optional<double>{std::nullopt}};
+    auto value213 = JSValue{std::optional<float>{std::nullopt}};
+
+    TestCheckEqual(JSValueType::Null, value201.Type());
+    TestCheckEqual(JSValueType::Null, value202.Type());
+    TestCheckEqual(JSValueType::Null, value203.Type());
+    TestCheckEqual(JSValueType::Null, value204.Type());
+    TestCheckEqual(JSValueType::Null, value205.Type());
+    TestCheckEqual(JSValueType::Null, value206.Type());
+    TestCheckEqual(JSValueType::Null, value207.Type());
+    TestCheckEqual(JSValueType::Null, value208.Type());
+    TestCheckEqual(JSValueType::Null, value209.Type());
+    TestCheckEqual(JSValueType::Null, value210.Type());
+    TestCheckEqual(JSValueType::Null, value211.Type());
+    TestCheckEqual(JSValueType::Null, value212.Type());
+    TestCheckEqual(JSValueType::Null, value213.Type());
+  }
+
   TEST_METHOD(TestJSValueImplicitCast) {
     // We do not assign values directly here sbecause it would be an explicit constructor call.
     JSValue value01, value02, value03, value04, value05, value06, value07, value08, value09, value10, value11, value12,

vnext/Microsoft.ReactNative.Cxx/JSValue.h

@@ -223,6 +223,14 @@ struct JSValue {
   //! Create a Double JSValue.
   JSValue(double value) noexcept;
 
+  //! Creates JSValue from std::optional<T>. The result type is defined by T.
+  //! If std::optional does not have value, then the result is JSValue::Null.
+  template <class T>
+  explicit JSValue(std::optional<T> &&value) noexcept;
+
+  //! Creates a Null JSValue.
+  explicit JSValue(std::nullopt_t) noexcept;
+
   //! Delete the copy constructor to avoid unexpected copies. Use the Copy method instead.
   JSValue(const JSValue &other) = delete;
 
@@ -607,6 +615,10 @@ inline JSValue::JSValue(TBool value) noexcept : m_type{JSValueType::Boolean}, m_
 template <class TInt, std::enable_if_t<std::is_integral_v<TInt> && !std::is_same_v<TInt, bool>, int>>
 inline JSValue::JSValue(TInt value) noexcept : m_type{JSValueType::Int64}, m_int64{static_cast<int64_t>(value)} {}
 inline JSValue::JSValue(double value) noexcept : m_type{JSValueType::Double}, m_double{value} {}
+template <class T>
+inline JSValue::JSValue(std::optional<T> &&value) noexcept
+    : JSValue(value.has_value() ? JSValue(std::move(value).value()) : JSValue()) {}
+inline JSValue::JSValue(std::nullopt_t) noexcept : JSValue{} {}
 #pragma warning(pop)
 
 inline JSValueType JSValue::Type() const noexcept {