Long live QML inline components

[ChangeLog][QtQml] It is now possible to declare new QML components in
a QML file via the component keyword. They can be used just as if they
were declared in another file, with the only difference that the type
name needs to be prefixed with the name of the containing type outside
of the file were the inline component has been declared.

Notably, inline components are not closures: In the following
example, the output would be 42

// MyItem.qml
Item {
    property int i: 33
    component IC: Item {
        Component.onCompleted: console.log(i)
    }
}
// user.qml
Item {
    property int i: 42
    MyItem.IC {}
}

Fixes: QTBUG-79382
Change-Id: I6a5ffc43f093a76323f435cfee9bab217781b8f5
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 161 insertions, 0 deletions

diff --git a/src/qml/inlinecomponentutils_p.h b/src/qml/inlinecomponentutils_p.h
new file mode 100644
index 0000000000..99b28349cd
--- /dev/null
+++ b/src/qml/inlinecomponentutils_p.h
@@ -0,0 +1,161 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef INLINECOMPONENTUTILS_P_H
+#define INLINECOMPONENTUTILS_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <private/qv4compileddata_p.h>
+#include <private/qv4executablecompilationunit_p.h>
+
+namespace icutils {
+struct Node {
+    Node() = default;
+    Node(const Node &) = default;
+    Node(Node &&) = default;
+    Node& operator=(Node const &) = default;
+    Node& operator=(Node &&) = default;
+    bool operator==(Node const &other) const {return index == other.index;}
+
+    Node(std::vector<QV4::CompiledData::InlineComponent>::size_type s) {
+        index = quint32(s);
+        temporaryMark = 0;
+        permanentMark = 0;
+    }
+
+    union {
+        quint32_le_bitfield<0, 30> index;
+        quint32_le_bitfield<30, 1> temporaryMark;
+        quint32_le_bitfield<31, 1> permanentMark;
+    };
+};
+
+using AdjacencyList = std::vector<std::vector<Node*>>;
+
+template<typename ObjectContainer, typename InlineComponent>
+void fillAdjacencyListForInlineComponents(ObjectContainer *objectContainer, AdjacencyList &adjacencyList, std::vector<Node> &nodes, const std::vector<InlineComponent> &allICs) {
+    using CompiledObject = typename ObjectContainer::CompiledObject;
+    // add an edge from A to B if A and B are inline components with the same containing type
+    // and A inherits from B (ignore indirect chains through external types for now)
+    // or if A instantiates B
+    for (typename std::vector<InlineComponent>::size_type i = 0; i < allICs.size(); ++i) {
+        const auto& ic = allICs[i];
+        const CompiledObject *obj = objectContainer->objectAt(ic.objectIndex);
+        QV4::ResolvedTypeReference *currentICTypeRef = objectContainer->resolvedType(ic.nameIndex);
+        auto createEdgeFromTypeRef = [&](QV4::ResolvedTypeReference *targetTypeRef) {
+            if (targetTypeRef && targetTypeRef->type.isInlineComponentType()) {
+                if (targetTypeRef->type.containingType() == currentICTypeRef->type.containingType()) {
+                    auto icIt = std::find_if(allICs.cbegin(), allICs.cend(), [&](const QV4::CompiledData::InlineComponent &icSearched){
+                        return int(icSearched.objectIndex) == targetTypeRef->type.inlineComponentObjectId();
+                    });
+                    Q_ASSERT(icIt != allICs.cend());
+                    Node& target = nodes[i];
+                    adjacencyList[std::distance(allICs.cbegin(), icIt)].push_back(&target);
+                }
+            }
+        };
+        if (obj->inheritedTypeNameIndex != 0) {
+            QV4::ResolvedTypeReference *parentTypeRef = objectContainer->resolvedType(obj->inheritedTypeNameIndex);
+            createEdgeFromTypeRef(parentTypeRef);
+
+        }
+        auto referencedInICObjectIndex = ic.objectIndex + 1;
+        while (int(referencedInICObjectIndex) < objectContainer->objectCount()) {
+            auto potentiallyReferencedInICObject = objectContainer->objectAt(referencedInICObjectIndex);
+            bool stillInIC = !(potentiallyReferencedInICObject-> flags & QV4::CompiledData::Object::IsInlineComponentRoot)
+                    && (potentiallyReferencedInICObject-> flags & QV4::CompiledData::Object::InPartOfInlineComponent);
+            if (!stillInIC)
+                break;
+            createEdgeFromTypeRef(objectContainer->resolvedType(potentiallyReferencedInICObject->inheritedTypeNameIndex));
+            ++referencedInICObjectIndex;
+        }
+    }
+};
+
+inline void topoVisit(Node *node, AdjacencyList &adjacencyList, bool &hasCycle, std::vector<Node> &nodesSorted) {
+    if (node->permanentMark)
+        return;
+    if (node->temporaryMark) {
+        hasCycle = true;
+        return;
+    }
+    node->temporaryMark = 1;
+
+    auto const &edges = adjacencyList[node->index];
+    for (auto edgeTarget =edges.begin(); edgeTarget != edges.end(); ++edgeTarget) {
+        topoVisit(*edgeTarget, adjacencyList, hasCycle, nodesSorted);
+    }
+
+    node->temporaryMark = 0;
+    node->permanentMark = 1;
+    nodesSorted.push_back(*node);
+};
+
+// Use DFS based topological sorting (https://en.wikipedia.org/wiki/Topological_sorting)
+inline std::vector<Node> topoSort(std::vector<Node> &nodes, AdjacencyList &adjacencyList, bool &hasCycle) {
+    std::vector<Node> nodesSorted;
+    nodesSorted.reserve(nodes.size());
+
+    hasCycle = false;
+    auto currentNodeIt = std::find_if(nodes.begin(), nodes.end(), [](const Node& node) {
+        return node.permanentMark == 0;
+    });
+    // Do a topological sort of all inline components
+    // afterwards, nodesSorted contains the nodes for the inline components in reverse topological order
+    while (currentNodeIt != nodes.end() && !hasCycle) {
+        Node& currentNode = *currentNodeIt;
+        topoVisit(&currentNode, adjacencyList, hasCycle, nodesSorted);
+        currentNodeIt = std::find_if(nodes.begin(), nodes.end(), [](const Node& node) {
+            return node.permanentMark == 0;
+        });
+    }
+    return nodesSorted;
+}
+}
+
+#endif // INLINECOMPONENTUTILS_P_H