Fix assertion failure nlohmann#3032

Additionally, add the previously failing case to the test suite.
carlsmedstad · Sep 27, 2021 · 1195701 · 1195701
1 parent 0b345b2
commit 1195701
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Showing 3 changed files with 37 additions and 6 deletions.
diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp
@@ -3695,14 +3695,23 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             if (idx >= m_value.array->size())
             {
 #if JSON_DIAGNOSTICS
-                // remember array size before resizing
+                // remember array size & capacity before resizing
                 const auto previous_size = m_value.array->size();
+                const auto old_capacity = m_value.array->capacity();
 #endif
                 m_value.array->resize(idx + 1);
 
 #if JSON_DIAGNOSTICS
-                // set parent for values added above
-                set_parents(begin() + static_cast<typename iterator::difference_type>(previous_size), static_cast<typename iterator::difference_type>(idx + 1 - previous_size));
+                if (JSON_HEDLEY_UNLIKELY(m_value.array->capacity() != old_capacity))
+                {
+                    // capacity has changed: update all parents
+                    set_parents();
+                }
+                else
+                {
+                    // set parent for values added above
+                    set_parents(begin() + static_cast<typename iterator::difference_type>(previous_size), static_cast<typename iterator::difference_type>(idx + 1 - previous_size));
+                }
 #endif
             }
 

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -21101,14 +21101,23 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             if (idx >= m_value.array->size())
             {
 #if JSON_DIAGNOSTICS
-                // remember array size before resizing
+                // remember array size & capacity before resizing
                 const auto previous_size = m_value.array->size();
+                const auto old_capacity = m_value.array->capacity();
 #endif
                 m_value.array->resize(idx + 1);
 
 #if JSON_DIAGNOSTICS
-                // set parent for values added above
-                set_parents(begin() + static_cast<typename iterator::difference_type>(previous_size), static_cast<typename iterator::difference_type>(idx + 1 - previous_size));
+                if (JSON_HEDLEY_UNLIKELY(m_value.array->capacity() != old_capacity))
+                {
+                    // capacity has changed: update all parents
+                    set_parents();
+                }
+                else
+                {
+                    // set parent for values added above
+                    set_parents(begin() + static_cast<typename iterator::difference_type>(previous_size), static_cast<typename iterator::difference_type>(idx + 1 - previous_size));
+                }
 #endif
             }
 

diff --git a/test/src/unit-diagnostics.cpp b/test/src/unit-diagnostics.cpp
@@ -234,4 +234,17 @@ TEST_CASE("Better diagnostics")
             root.push_back(lower);
         }
     }
+
+    SECTION("Regression test for https://github.com/nlohmann/json/issues/3032")
+    {
+        // reference operator[](size_type idx)
+        {
+            json j_arr = json::array();
+            j_arr[0] = "STRING";
+            j_arr[1] = "STRING";
+            j_arr[2] = "STRING";
+            j_arr[4] = "STRING";
+            json j_arr_copy = j_arr;
+        }
+    }
 }