QUrl: restore empty-but-not-null for components that are present

This got lost during the QStringView port that happend in Qt 6.0
(commit 548dcef08976649c820054f3db1ad108c72439cd) because
QString::operator+=(QStringView) does not copy the nullness of the right
side, whereas QString::operator+=(const QString &) does.

Pick-to: 6.2 6.4 6.5
Fixes: QTBUG-84315
Change-Id: Ide4dbd0777a44ed0870efffd17399b772d34fd55
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 8 insertions, 6 deletions

diff --git a/src/corelib/io/qurl.cpp b/src/corelib/io/qurl.cpp
index f925b2c901..0d42a78422 100644
--- a/src/corelib/io/qurl.cpp
+++ b/src/corelib/io/qurl.cpp
@@ -818,14 +818,16 @@ recodeFromUser(const QString &input, const ushort *actions, qsizetype from, qsiz
 static inline void appendToUser(QString &appendTo, QStringView value, QUrl::FormattingOptions options,
                                 const ushort *actions)
 {
-    // Test ComponentFormattingOptions, ignore FormattingOptions.
-    if ((options & 0xFFFF0000) == QUrl::PrettyDecoded) {
+    // The stored value is already QUrl::PrettyDecoded, so there's nothing to
+    // do if that's what the user asked for (test only
+    // ComponentFormattingOptions, ignore FormattingOptions).
+    if ((options & 0xFFFF0000) == QUrl::PrettyDecoded ||
+            !qt_urlRecode(appendTo, value, options, actions))
         appendTo += value;
-        return;
-    }
 
-    if (!qt_urlRecode(appendTo, value, options, actions))
-        appendTo += value;
+    // copy nullness, if necessary, because QString::operator+=(QStringView) doesn't
+    if (appendTo.isNull() && !value.isNull())
+        appendTo.detach();
 }
 
 inline void QUrlPrivate::appendAuthority(QString &appendTo, QUrl::FormattingOptions options, Section appendingTo) const