Set parent pointers for values inserted via update() (fixes #3007). (#3008)

* Set parent pointers for values inserted via update() (fixes #3007).

* Moved test for #3007 to proper file.

* Enable access to private members in diagnostics unit tests.

* Make style consistent with rest of code.

* Forced amalgamate rerun.

* Refactor test for #3007 so it doesn't use private members. Also extend to test both update() functions.

* Added fix for #3007 to update(const_iterator, const_iterator) as well.

* Added failing example code from #3007 as extra test.

include/nlohmann/json.hpp

@@ -6009,6 +6009,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         for (auto it = j.cbegin(); it != j.cend(); ++it)
         {
             m_value.object->operator[](it.key()) = it.value();
+#if JSON_DIAGNOSTICS
+            m_value.object->operator[](it.key()).m_parent = this;
+#endif
         }
     }
 
@@ -6069,6 +6072,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         for (auto it = first; it != last; ++it)
         {
             m_value.object->operator[](it.key()) = it.value();
+#if JSON_DIAGNOSTICS
+            m_value.object->operator[](it.key()).m_parent = this;
+#endif
         }
     }
 

single_include/nlohmann/json.hpp

@@ -23414,6 +23414,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         for (auto it = j.cbegin(); it != j.cend(); ++it)
         {
             m_value.object->operator[](it.key()) = it.value();
+#if JSON_DIAGNOSTICS
+            m_value.object->operator[](it.key()).m_parent = this;
+#endif
         }
     }
 
@@ -23474,6 +23477,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         for (auto it = first; it != last; ++it)
         {
             m_value.object->operator[](it.key()) = it.value();
+#if JSON_DIAGNOSTICS
+            m_value.object->operator[](it.key()).m_parent = this;
+#endif
         }
     }
 

test/src/unit-diagnostics.cpp

@@ -184,4 +184,54 @@ TEST_CASE("Better diagnostics")
         j["second"] = value;
         j2["something"] = j;
     }
+
+    SECTION("Regression test for issue #3007 - Parent pointers properly set when using update()")
+    {
+        // void update(const_reference j)
+        {
+            json j = json::object();
+
+            {
+                json j2 = json::object();
+                j2["one"] = 1;
+
+                j.update(j2);
+            }
+
+            // Must call operator[] on const element, otherwise m_parent gets updated.
+            auto const& constJ = j;
+            CHECK_THROWS_WITH_AS(constJ["one"].at(0), "[json.exception.type_error.304] (/one) cannot use at() with number", json::type_error);
+        }
+
+        // void update(const_iterator first, const_iterator last)
+        {
+            json j = json::object();
+
+            {
+                json j2 = json::object();
+                j2["one"] = 1;
+
+                j.update(j2.begin(), j2.end());
+            }
+
+            // Must call operator[] on const element, otherwise m_parent gets updated.
+            auto const& constJ = j;
+            CHECK_THROWS_WITH_AS(constJ["one"].at(0), "[json.exception.type_error.304] (/one) cannot use at() with number", json::type_error);
+        }
+
+        // Code from #3007 triggering unwanted assertion without fix to update().
+        {
+            json root = json::array();
+            json lower = json::object();
+
+            {
+                json lowest = json::object();
+                lowest["one"] = 1;
+
+                lower.update(lowest);
+            }
+
+            root.push_back(lower);
+        }
+    }
 }