cxx-qt-lib: use a QVariantValue trait so that custom types can be used

Closes KDAB#395

Author: ahayzen-kdab

CHANGELOG.md

@@ -19,6 +19,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Support for container types: `QSet<T>`, `QHash<K, V>`, `QMap<K, V>`, `QVector<T>`
 - Support for further types: `QModelIndex`, `QPersistentModelIndex`
 
+### Changed
+
+- `QVariant` now has a uses a `QVariantValue` trait for supported types, allowing custom types to be used with QVariant
+
 ### Fixed
 
 - Support for generating correct C++ code for `Pin<T>` Rust types

crates/cxx-qt-lib-headers/include/qvariant.h

@@ -7,6 +7,8 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 #pragma once
 
+#include <cstdint>
+
 #include <QVariant>
 
 #include <QColor>
@@ -31,54 +33,51 @@ struct rust::IsRelocatable<QVariant> : std::true_type
 
 namespace rust {
 namespace cxxqtlib1 {
-
-namespace types {
-
-enum class QVariantType : uint8_t
-{
-  Unsupported = 0,
-  Bool = 1,
-  F32 = 2,
-  F64 = 3,
-  I8 = 4,
-  I16 = 5,
-  I32 = 6,
-  QColor = 7,
-  QDate = 8,
-  QDateTime = 9,
-  QPoint = 10,
-  QPointF = 11,
-  QRect = 12,
-  QRectF = 13,
-  QSize = 14,
-  QSizeF = 15,
-  QString = 16,
-  QTime = 17,
-  QUrl = 18,
-  U8 = 19,
-  U16 = 20,
-  U32 = 21,
-};
-
-} // namespace types
+namespace qvariant {
 
 template<typename T>
 QVariant
-qvariantInitFromT(T value)
+qvariantConstruct(const T& value) noexcept
 {
-  return QVariant::fromValue(value);
+  return QVariant::fromValue<T>(value);
 }
 
-types::QVariantType
-qvariantType(const QVariant& variant);
-
 template<typename T>
 T
-qvariantToT(const QVariant& variant)
+qvariantValue(const QVariant& variant) noexcept
 {
-  Q_ASSERT(variant.canConvert<T>());
   return variant.value<T>();
 }
 
+// Need to use a macro here as we can't template because the types
+// are always QVariant and bool. So then CXX can't decide which to use.
+#define CXX_QT_QVARIANT_CAN_CONVERT(name)                                      \
+  bool qvariantCanConvert##name(const QVariant& variant);
+
+CXX_QT_QVARIANT_CAN_CONVERT(Bool)
+CXX_QT_QVARIANT_CAN_CONVERT(F32)
+CXX_QT_QVARIANT_CAN_CONVERT(F64)
+CXX_QT_QVARIANT_CAN_CONVERT(I8)
+CXX_QT_QVARIANT_CAN_CONVERT(I16)
+CXX_QT_QVARIANT_CAN_CONVERT(I32)
+CXX_QT_QVARIANT_CAN_CONVERT(I64)
+CXX_QT_QVARIANT_CAN_CONVERT(QColor)
+CXX_QT_QVARIANT_CAN_CONVERT(QDate)
+CXX_QT_QVARIANT_CAN_CONVERT(QDateTime)
+CXX_QT_QVARIANT_CAN_CONVERT(QPoint)
+CXX_QT_QVARIANT_CAN_CONVERT(QPointF)
+CXX_QT_QVARIANT_CAN_CONVERT(QRect)
+CXX_QT_QVARIANT_CAN_CONVERT(QRectF)
+CXX_QT_QVARIANT_CAN_CONVERT(QSize)
+CXX_QT_QVARIANT_CAN_CONVERT(QSizeF)
+CXX_QT_QVARIANT_CAN_CONVERT(QString)
+CXX_QT_QVARIANT_CAN_CONVERT(QTime)
+CXX_QT_QVARIANT_CAN_CONVERT(QUrl)
+CXX_QT_QVARIANT_CAN_CONVERT(U8)
+CXX_QT_QVARIANT_CAN_CONVERT(U16)
+CXX_QT_QVARIANT_CAN_CONVERT(U32)
+CXX_QT_QVARIANT_CAN_CONVERT(U64)
+
+}
 }
 }

crates/cxx-qt-lib/build.rs

@@ -51,7 +51,30 @@ fn main() {
         "qstring",
         "qtime",
         "qurl",
-        "qvariant",
+        "qvariant/mod",
+        "qvariant/qvariant_bool",
+        "qvariant/qvariant_f32",
+        "qvariant/qvariant_f64",
+        "qvariant/qvariant_i8",
+        "qvariant/qvariant_i16",
+        "qvariant/qvariant_i32",
+        "qvariant/qvariant_i64",
+        "qvariant/qvariant_qcolor",
+        "qvariant/qvariant_qdate",
+        "qvariant/qvariant_qdatetime",
+        "qvariant/qvariant_qpoint",
+        "qvariant/qvariant_qpointf",
+        "qvariant/qvariant_qrect",
+        "qvariant/qvariant_qrectf",
+        "qvariant/qvariant_qsize",
+        "qvariant/qvariant_qsizef",
+        "qvariant/qvariant_qstring",
+        "qvariant/qvariant_qtime",
+        "qvariant/qvariant_qurl",
+        "qvariant/qvariant_u8",
+        "qvariant/qvariant_u16",
+        "qvariant/qvariant_u32",
+        "qvariant/qvariant_u64",
         "qvector/qvector_bool",
         "qvector/qvector_f32",
         "qvector/qvector_f64",
@@ -111,7 +134,7 @@ fn main() {
         "qstring",
         "qtime",
         "qurl",
-        "qvariant",
+        "qvariant/qvariant",
         "qvector/qvector",
     ];
     for cpp_file in cpp_files {