SQL/SQLite: add case folding for non-ascii characters

SQLite does not provide a proper case folding for non-ascii characters
due to a lack of a proper ICU library. Therefore add an option so Qt can
do it for SQLite.
[ChangeLog][SQL][SQLite] Add new option
QSQLITE_ENABLE_NON_ASCII_CASE_FOLDING for correct case folding of
non-ascii characters.

Fixes: QTBUG-18871
Change-Id: Ib62fedf750f05e50a581604253cf30d81e367b42
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/sqldrivers/sqlite/qsql_sqlite.cpp

@@ -625,6 +625,30 @@ static void _q_regexp_cleanup(void *cache)
 }
 #endif
 
+static void _q_lower(sqlite3_context* context, int argc, sqlite3_value** argv)
+{
+    if (Q_UNLIKELY(argc != 1)) {
+        sqlite3_result_text(context, nullptr, 0, nullptr);
+        return;
+    }
+    const QString lower = QString::fromUtf8(
+        reinterpret_cast<const char*>(sqlite3_value_text(argv[0]))).toLower();
+    const QByteArray ba = lower.toUtf8();
+    sqlite3_result_text(context, ba.data(), ba.size(), SQLITE_TRANSIENT);
+}
+
+static void _q_upper(sqlite3_context* context, int argc, sqlite3_value** argv)
+{
+    if (Q_UNLIKELY(argc != 1)) {
+        sqlite3_result_text(context, nullptr, 0, nullptr);
+        return;
+    }
+    const QString upper = QString::fromUtf8(
+        reinterpret_cast<const char*>(sqlite3_value_text(argv[0]))).toUpper();
+    const QByteArray ba = upper.toUtf8();
+    sqlite3_result_text(context, ba.data(), ba.size(), SQLITE_TRANSIENT);
+}
+
 QSQLiteDriver::QSQLiteDriver(QObject * parent)
     : QSqlDriver(*new QSQLiteDriverPrivate, parent)
 {
@@ -692,6 +716,7 @@ bool QSQLiteDriver::open(const QString & db, const QString &, const QString &, c
     bool openUriOption = false;
     bool useExtendedResultCodes = true;
     bool useQtVfs = false;
+    bool useQtCaseFolding = false;
 #if QT_CONFIG(regularexpression)
     static const auto regexpConnectOption = "QSQLITE_ENABLE_REGEXP"_L1;
     bool defineRegexp = false;
@@ -719,6 +744,8 @@ bool QSQLiteDriver::open(const QString & db, const QString &, const QString &, c
             sharedCache = true;
         } else if (option == "QSQLITE_NO_USE_EXTENDED_RESULT_CODES"_L1) {
             useExtendedResultCodes = false;
+        } else if (option == "QSQLITE_ENABLE_NON_ASCII_CASE_FOLDING"_L1) {
+            useQtCaseFolding = true;
         }
 #if QT_CONFIG(regularexpression)
         else if (option.startsWith(regexpConnectOption)) {
@@ -760,6 +787,12 @@ bool QSQLiteDriver::open(const QString & db, const QString &, const QString &, c
                                        nullptr, &_q_regexp_cleanup);
         }
 #endif
+        if (useQtCaseFolding) {
+            sqlite3_create_function_v2(d->access, "lower", 1, SQLITE_UTF8, nullptr,
+                                       &_q_lower, nullptr, nullptr, nullptr);
+            sqlite3_create_function_v2(d->access, "upper", 1, SQLITE_UTF8, nullptr,
+                                       &_q_upper, nullptr, nullptr, nullptr);
+        }
         return true;
     } else {
         setLastError(qMakeError(d->access, tr("Error opening database"),

src/sql/doc/src/sql-driver.qdoc

@@ -757,6 +757,10 @@
       \li QSQLITE_NO_USE_EXTENDED_RESULT_CODES
       \li Disables the usage of the \l {https://www.sqlite.org/c3ref/extended_result_codes.html}
           {extended result code} feature in SQLite (for backwards compatibility)
+    \row
+      \li QSQLITE_ENABLE_NON_ASCII_CASE_FOLDING
+      \li If set, the plugin replaces the functions 'lower' and 'upper' with
+          QString functions for correct case folding of non-ascii characters
     \endtable
 
     \section3 How to Build the QSQLITE Plugin

tests/auto/sql/kernel/qsqldatabase/tst_databases.h

@@ -118,12 +118,14 @@ public:
         if (port > 0)
             cName += QLatin1Char(':') + QString::number(port);
 
+        QString opts = params;
         if (driver == "QSQLITE") {
             // Since the database for sqlite is generated at runtime it's always
             // available, but we use QTempDir so it's always in a different
             // location. Thus, let's ignore the path completely.
             cName = "SQLite";
             qInfo("SQLite will use the database located at %ls", qUtf16Printable(dbName));
+            opts += QStringLiteral(";QSQLITE_ENABLE_NON_ASCII_CASE_FOLDING");
         }
 
         auto db = QSqlDatabase::addDatabase(driver, cName);
@@ -137,7 +139,7 @@ public:
         db.setPassword(passwd);
         db.setHostName(host);
         db.setPort(port);
-        db.setConnectOptions(params);
+        db.setConnectOptions(opts);
         dbNames.append(cName);
     }
 

tests/auto/sql/kernel/qsqlquery/tst_qsqlquery.cpp

@@ -4454,7 +4454,7 @@ void tst_QSqlQuery::aggregateFunctionTypes()
                             .arg(tableName)));
 
         QVERIFY_SQL(q, exec("SELECT MAX(txt) FROM " + tableName));
-        QVERIFY(q.next());
+        QVERIFY_SQL(q, next());
         if (dbType == QSqlDriver::SQLite)
             QCOMPARE(q.record().field(0).metaType().id(), QMetaType::UnknownType);
         else
@@ -4469,6 +4469,19 @@ void tst_QSqlQuery::aggregateFunctionTypes()
         QVERIFY(q.next());
         QCOMPARE(q.value(0).toString(), QLatin1String("upper"));
         QCOMPARE(q.record().field(0).metaType().id(), QMetaType::QString);
+
+        QVERIFY_SQL(q, exec(QLatin1String("DELETE FROM %1").arg(tableName)));
+        QVERIFY_SQL(q, exec(QString::fromUtf8("INSERT INTO %1 (id, txt) VALUES (1, 'löW€RÄ')")
+                            .arg(tableName)));
+        QVERIFY_SQL(q, exec("SELECT LOWER(txt) FROM " + tableName));
+        QVERIFY(q.next());
+        QCOMPARE(q.value(0).toString(), QString::fromUtf8("löw€rä"));
+        QCOMPARE(q.record().field(0).metaType().id(), QMetaType::QString);
+
+        QVERIFY_SQL(q, exec("SELECT UPPER(txt) FROM " + tableName));
+        QVERIFY(q.next());
+        QCOMPARE(q.value(0).toString(), QString::fromUtf8("LÖW€RÄ"));
+        QCOMPARE(q.record().field(0).metaType().id(), QMetaType::QString);
     }
 }