QSettings: port key processing to QAnyStringView

... in preparation for replacing the QString keys in the public API
with QAnyStringView ones.

This removes the "important optimization" that avoids a detach in the
common case where the input is the same as the output of
normalization. But that optimization is beside the point, because it
trades a memory allocation avoided in the library for O(N) allocations
inserted into user code for each call to QSettings::value(), the vast
majority of which are calls with string literals.

With the public interface ported to QAnyStringView in the follow-up
patch, we can then internally optimize memory allocations _in a central
place_ (e.g. by returning std::u16string or QVarLengthArray<QChar> from
normalizeKey() instead of QString). But first we need to get rid of all
the unwarranted allocations in user code.

Change-Id: I45fc83d972c552a220c9c29508001d3f172e1162
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

1 files changed, 12 insertions, 15 deletions

diff --git a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
index c4ede66381..e8bef28c02 100644
--- a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
+++ b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -2160,20 +2160,17 @@ void tst_QSettings::testNormalizedKey()
 
     inKey.detach();
 
-    QString result = QSettingsPrivate::normalizedKey(inKey);
-    QCOMPARE(result, outKey);
-
-    /*
-        If the key is already normalized, we verify that outKey is
-        just a shallow copy of the input string. This is an important
-        optimization that shouldn't be removed accidentally.
-    */
-    if (inKey == outKey) {
-        QVERIFY(!result.isDetached());
-    } else {
-        if (!result.isEmpty()) {
-            QVERIFY(result.isDetached());
-        }
+    {
+        auto result = QSettingsPrivate::normalizedKey(inKey);
+        QCOMPARE(result, outKey);
+    }
+    {
+        auto result = QSettingsPrivate::normalizedKey(QUtf8StringView{inKey.toUtf8()});
+        QCOMPARE(result, outKey);
+    }
+    {
+        auto result = QSettingsPrivate::normalizedKey(QLatin1String{inKey.toLatin1()});
+        QCOMPARE(result, outKey);
     }
 }
 #endif