From b7f40416692c357b440c885fe18fa70e2a829820 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Tue, 16 Nov 2021 14:59:30 +0100
Subject: [PATCH] QAnyStringView: fix broken implicit conversion from
 QStringBuilder

Need to use QConcatenable<>::ConvertTo for SFINAE, the forwarded type
alias in QStringBuilder itself doesn't work.

[ChangeLog][QtCore][QAnyStringView/QStringBuilder] Implicit conversion
from QStringBuilder to QAnyStringView now works as advertised.

Pick-to: 6.2
Fixes: QTBUG-98138
Change-Id: I1c300675cf43b13017bc56398ae5d8c1c51e64fe
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/corelib/text/qanystringview.h              |  3 ++-
 src/corelib/text/qstringbuilder.h              |  2 +-
 .../text/qanystringview/tst_qanystringview.cpp | 18 ++++++++++++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/corelib/text/qanystringview.h b/src/corelib/text/qanystringview.h
index 68754931e9..774651cb6a 100644
--- a/src/corelib/text/qanystringview.h
+++ b/src/corelib/text/qanystringview.h
@@ -50,6 +50,7 @@
 QT_BEGIN_NAMESPACE
 
 template <typename, typename> class QStringBuilder;
+template <typename> struct QConcatenable;
 
 class QAnyStringView
 {
@@ -163,7 +164,7 @@ public:
     // defined in qstringbuilder.h
     template <typename A, typename B>
     inline QAnyStringView(const QStringBuilder<A, B> &expr,
-                          typename QStringBuilder<A, B>::ConvertTo &&capacity = {});
+                          typename QConcatenable<QStringBuilder<A, B>>::ConvertTo &&capacity = {});
 
     template <typename Container, if_compatible_container<Container> = true>
     constexpr QAnyStringView(const Container &c) noexcept
diff --git a/src/corelib/text/qstringbuilder.h b/src/corelib/text/qstringbuilder.h
index 5a6a531e74..8494459d63 100644
--- a/src/corelib/text/qstringbuilder.h
+++ b/src/corelib/text/qstringbuilder.h
@@ -468,7 +468,7 @@ QString &operator+=(QString &a, const QStringBuilder<A, B> &b)
 
 template <typename A, typename B>
 QAnyStringView::QAnyStringView(const QStringBuilder<A, B> &expr,
-                               typename QStringBuilder<A, B>::ConvertTo &&capacity)
+                               typename QConcatenable<QStringBuilder<A, B>>::ConvertTo &&capacity)
     : QAnyStringView(capacity = expr) {}
 
 QT_END_NAMESPACE
diff --git a/tests/auto/corelib/text/qanystringview/tst_qanystringview.cpp b/tests/auto/corelib/text/qanystringview/tst_qanystringview.cpp
index bbc0bdacfd..e5e3ac9f84 100644
--- a/tests/auto/corelib/text/qanystringview/tst_qanystringview.cpp
+++ b/tests/auto/corelib/text/qanystringview/tst_qanystringview.cpp
@@ -30,6 +30,7 @@
 #include <QChar>
 #include <QList>
 #include <QString>
+#include <QStringBuilder>
 #include <QVarLengthArray>
 
 #include <QTest>
@@ -230,6 +231,12 @@ static_assert(CanConvert<std::array<wchar_t, 123>> == CanConvertFromWCharT);
 static_assert(!CanConvert<std::deque<wchar_t>>);
 static_assert(!CanConvert<std::list<wchar_t>>);
 
+//
+// QStringBuilder
+//
+
+static_assert(CanConvert<QStringBuilder<QString, QString>>);
+
 
 class tst_QAnyStringView : public QObject
 {
@@ -303,9 +310,13 @@ private Q_SLOTS:
     void fromChar16TContainers() const { fromContainers<char16_t>(); }
     void fromWCharTContainers() const { ONLY_WIN(fromContainers<wchar_t>()); }
 
+    void fromQStringBuilder_QString_QString() const { fromQStringBuilder(u"1"_qs % u"2"_qs, u"12"); }
+
     void comparison();
 
 private:
+    template <typename StringBuilder>
+    void fromQStringBuilder(StringBuilder &&sb, QStringView expected) const;
     template <typename Char>
     void fromArray() const;
     template <typename String>
@@ -419,6 +430,13 @@ void tst_QAnyStringView::basics() const
     QVERIFY(!(sv2 != sv1));
 }
 
+template <typename StringBuilder>
+void tst_QAnyStringView::fromQStringBuilder(StringBuilder &&sb, QStringView expected) const
+{
+    auto toAnyStringView = [](QAnyStringView sv) { return sv; };
+    QCOMPARE(toAnyStringView(std::forward<StringBuilder>(sb)), expected);
+}
+
 template <typename Char>
 void tst_QAnyStringView::fromArray() const
 {