From 10ec0f21b0418dbffccd09504238c6816b16fa4d Mon Sep 17 00:00:00 2001
From: Benoit Blanchon <git@benoitblanchon.fr>
Date: Fri, 23 Oct 2020 10:22:14 +0200
Subject: [PATCH] Fixed `operator|(MemberProxy, JsonObject)` (fixes #1415)

---
 CHANGELOG.md                                 |  1 +
 extras/tests/JsonDocument/MemberProxy.cpp    | 11 +++++++++++
 src/ArduinoJson/Array/ElementProxy.hpp       |  5 ++++-
 src/ArduinoJson/Object/MemberProxy.hpp       |  5 ++++-
 src/ArduinoJson/Variant/VariantOperators.hpp | 14 ++++++++++++--
 src/ArduinoJson/Variant/VariantRef.hpp       |  6 ++----
 src/ArduinoJson/Variant/VariantTag.hpp       | 16 ++++++++++++++++
 7 files changed, 50 insertions(+), 8 deletions(-)
 create mode 100644 src/ArduinoJson/Variant/VariantTag.hpp

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 13224494..98254812 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Fixed error `ambiguous overload for 'operator|'` (issue #1411)
+* Fixed `operator|(MemberProxy, JsonObject)` (issue #1415)
 
 v6.17.0 (2020-10-19)
 -------
diff --git a/extras/tests/JsonDocument/MemberProxy.cpp b/extras/tests/JsonDocument/MemberProxy.cpp
index ded18157..ecb41c5c 100644
--- a/extras/tests/JsonDocument/MemberProxy.cpp
+++ b/extras/tests/JsonDocument/MemberProxy.cpp
@@ -121,6 +121,17 @@ TEST_CASE("MemberProxy::operator|()") {
 
     REQUIRE(sensor == std::string("gps"));
   }
+
+  SECTION("Issue #1415") {
+    JsonObject object = doc.to<JsonObject>();
+    object["hello"] = "world";
+
+    StaticJsonDocument<0> emptyDoc;
+    JsonObject anotherObject = object["hello"] | emptyDoc.to<JsonObject>();
+
+    REQUIRE(anotherObject.isNull() == false);
+    REQUIRE(anotherObject.size() == 0);
+  }
 }
 
 TEST_CASE("MemberProxy::remove()") {
diff --git a/src/ArduinoJson/Array/ElementProxy.hpp b/src/ArduinoJson/Array/ElementProxy.hpp
index 6d47ef37..41166b6a 100644
--- a/src/ArduinoJson/Array/ElementProxy.hpp
+++ b/src/ArduinoJson/Array/ElementProxy.hpp
@@ -19,10 +19,13 @@ namespace ARDUINOJSON_NAMESPACE {
 template <typename TArray>
 class ElementProxy : public VariantOperators<ElementProxy<TArray> >,
                      public VariantShortcuts<ElementProxy<TArray> >,
-                     public Visitable {
+                     public Visitable,
+                     public VariantTag {
   typedef ElementProxy<TArray> this_type;
 
  public:
+  typedef VariantRef variant_type;
+
   FORCE_INLINE ElementProxy(TArray array, size_t index)
       : _array(array), _index(index) {}
 
diff --git a/src/ArduinoJson/Object/MemberProxy.hpp b/src/ArduinoJson/Object/MemberProxy.hpp
index a9ee6034..1963deae 100644
--- a/src/ArduinoJson/Object/MemberProxy.hpp
+++ b/src/ArduinoJson/Object/MemberProxy.hpp
@@ -21,10 +21,13 @@ namespace ARDUINOJSON_NAMESPACE {
 template <typename TObject, typename TStringRef>
 class MemberProxy : public VariantOperators<MemberProxy<TObject, TStringRef> >,
                     public VariantShortcuts<MemberProxy<TObject, TStringRef> >,
-                    public Visitable {
+                    public Visitable,
+                    public VariantTag {
   typedef MemberProxy<TObject, TStringRef> this_type;
 
  public:
+  typedef VariantRef variant_type;
+
   FORCE_INLINE MemberProxy(TObject variant, TStringRef key)
       : _object(variant), _key(key) {}
 
diff --git a/src/ArduinoJson/Variant/VariantOperators.hpp b/src/ArduinoJson/Variant/VariantOperators.hpp
index b08d92f4..df4e9df2 100644
--- a/src/ArduinoJson/Variant/VariantOperators.hpp
+++ b/src/ArduinoJson/Variant/VariantOperators.hpp
@@ -9,6 +9,7 @@
 #include <ArduinoJson/Polyfills/attributes.hpp>
 #include <ArduinoJson/Polyfills/type_traits.hpp>
 #include <ArduinoJson/Variant/VariantAs.hpp>
+#include <ArduinoJson/Variant/VariantTag.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -17,15 +18,24 @@ CompareResult compare(const T1 &lhs, const T2 &rhs);  // VariantCompare.cpp
 
 template <typename TVariant>
 struct VariantOperators {
-  // Returns the default value if the VariantRef is undefined of incompatible
+  // Returns the default value if the VariantRef is undefined or incompatible
   template <typename T>
-  friend typename enable_if<!IsVisitable<T>::value, T>::type operator|(
+  friend typename enable_if<!IsVariant<T>::value, T>::type operator|(
       const TVariant &variant, T defaultValue) {
     if (variant.template is<T>())
       return variant.template as<T>();
     else
       return defaultValue;
   }
+  // Returns the default value if the VariantRef is undefined or incompatible
+  template <typename T>
+  friend typename enable_if<IsVariant<T>::value, typename T::variant_type>::type
+  operator|(const TVariant &variant, T defaultValue) {
+    if (variant)
+      return variant;
+    else
+      return defaultValue;
+  }
 
   // value == TVariant
   template <typename T>
diff --git a/src/ArduinoJson/Variant/VariantRef.hpp b/src/ArduinoJson/Variant/VariantRef.hpp
index c82ec1ea..a8b9067a 100644
--- a/src/ArduinoJson/Variant/VariantRef.hpp
+++ b/src/ArduinoJson/Variant/VariantRef.hpp
@@ -16,6 +16,7 @@
 #include <ArduinoJson/Variant/VariantOperators.hpp>
 #include <ArduinoJson/Variant/VariantRef.hpp>
 #include <ArduinoJson/Variant/VariantShortcuts.hpp>
+#include <ArduinoJson/Variant/VariantTag.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -23,12 +24,9 @@ namespace ARDUINOJSON_NAMESPACE {
 class ArrayRef;
 class ObjectRef;
 
-template <typename, typename>
-class MemberProxy;
-
 // Contains the methods shared by VariantRef and VariantConstRef
 template <typename TData>
-class VariantRefBase {
+class VariantRefBase : public VariantTag {
  public:
   // Tells wether the variant has the specified type.
   // Returns true if the variant has type type T, false otherwise.
diff --git a/src/ArduinoJson/Variant/VariantTag.hpp b/src/ArduinoJson/Variant/VariantTag.hpp
new file mode 100644
index 00000000..e9a08aec
--- /dev/null
+++ b/src/ArduinoJson/Variant/VariantTag.hpp
@@ -0,0 +1,16 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+struct VariantTag {};
+
+template <typename T>
+struct IsVariant : is_base_of<VariantTag, T> {};
+
+}  // namespace ARDUINOJSON_NAMESPACE