From 9f63577dddfb01a9b78d6222b15489ee2320d82a Mon Sep 17 00:00:00 2001
From: Volker Hilsheimer <volker.hilsheimer@qt.io>
Date: Sun, 23 Mar 2025 09:58:29 +0100
Subject: [PATCH] QGIM: test if a tuple row is valid before dereferencing

Row types that are convertible to bool, such as pointers, but also
unique_ptr and similar wrappers, should not be dereferenced when
accessing values for reading or writing. This is already done implicitly
when operating on single-value types, but for tuples we have to do so
explicitly, before accessing the element.

For example, inserting a row where the row type is a pointer will leave
that row be nullptr in the range, and both data and setData should fail
until a row has been constructed. For rows that are pointers to tuples,
we must never call get<>, as get cannot test if the item received is a
nullptr and still return a valid value (reference).

Since e.g. unique_ptr is explicitly convertible to bool we have to use
std::is_constructible rather than is_convertible, as the latter only
works for types that are implicitly convertible.

Change-Id: I9dbdf6e5cac0146ed5d1b88c523e182590b0c8ab
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
---
 src/corelib/itemmodels/qgenericitemmodel.h      | 6 +++---
 src/corelib/itemmodels/qgenericitemmodel_impl.h | 9 +++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/corelib/itemmodels/qgenericitemmodel.h b/src/corelib/itemmodels/qgenericitemmodel.h
index 0f62bd966cd..90c5eadcb39 100644
--- a/src/corelib/itemmodels/qgenericitemmodel.h
+++ b/src/corelib/itemmodels/qgenericitemmodel.h
@@ -277,7 +277,7 @@ public:
                 readData(*std::next(std::cbegin(row), index.column()));
             else if constexpr (static_column_count == 0)
                 readData(row);
-            else
+            else if (QGenericItemModelDetails::isValid(row))
                 for_element_at(row, index.column(), readData);
         }
         return result;
@@ -328,7 +328,7 @@ public:
                 success = writeData(*std::next(std::begin(row), index.column()));
             } else if constexpr (static_column_count == 0) {
                 success = writeData(row);
-            } else {
+            } else if (QGenericItemModelDetails::isValid(row)) {
                 for_element_at(row, index.column(), [&writeData, &success](auto &&target){
                     using target_type = decltype(target);
                     // we can only assign to an lvalue reference
@@ -361,7 +361,7 @@ public:
             } else if constexpr (static_column_count == 0) {
                 row = row_type{};
                 success = true;
-            } else {
+            } else if (QGenericItemModelDetails::isValid(row)) {
                 for_element_at(row, index.column(), [&success](auto &&target){
                     using target_type = decltype(target);
                     if constexpr (std::is_lvalue_reference_v<target_type>
diff --git a/src/corelib/itemmodels/qgenericitemmodel_impl.h b/src/corelib/itemmodels/qgenericitemmodel_impl.h
index a017f5c94e6..a3397957d29 100644
--- a/src/corelib/itemmodels/qgenericitemmodel_impl.h
+++ b/src/corelib/itemmodels/qgenericitemmodel_impl.h
@@ -178,6 +178,15 @@ namespace QGenericItemModelDetails
     template <typename T> static auto pointerTo(T &t) { return std::addressof(t); }
     template <typename T> static auto pointerTo(const T &&t) = delete;
 
+    template <typename T>
+    static bool isValid(T &&t)
+    {
+        if constexpr (std::is_constructible_v<bool, T>)
+            return bool(t);
+        else
+            return true;
+    }
+
     template <typename It>
     auto key(It&& it) -> decltype(it.key()) { return it.key(); }