New function for detecting mixed RTL-LTR texts

Qt's isRightToLeft() returns true only for all left-to-right characters
in the string. That prevents the automatic switch to LTR Text mode, when
the text contains one or more left-to-right characters.

See #1793 and #1929

src/Data.cpp

@@ -43,6 +43,21 @@ bool isTextOnly(QByteArray data, const QString& encoding, bool quickTest)
     }
 }
 
+bool containsRightToLeft(const QString& text) {
+
+    for(QChar ch : text) {
+        switch(ch.direction()) {
+        case QChar::DirR:
+        case QChar::DirAL:
+        case QChar::DirRLE:
+        case QChar::DirRLO:
+        case QChar::DirRLI:
+            return true;
+        }
+    }
+    return false;
+}
+
 bool startsWithBom(const QByteArray& data)
 {
     if(data.startsWith(bom3) ||

src/Data.h

@@ -10,6 +10,9 @@
 // text but makes it less reliable
 bool isTextOnly(QByteArray data, const QString& encoding = QString(), bool quickTest = false);
 
+// This returns true if text contains some character whose direction is right-to-left.
+bool containsRightToLeft(const QString& text);
+
 // This function returns true if the data in the data parameter starts with a Unicode BOM. Otherwise it returns false.
 bool startsWithBom(const QByteArray& data);
 

src/EditDialog.cpp

@@ -816,7 +816,7 @@ void EditDialog::editTextChanged()
 
             // Switch to the Qt Editor if we detect right-to-left text,
             // since the QScintilla editor does not support it.
-            if (sciEdit->text().isRightToLeft())
+            if (containsRightToLeft(sciEdit->text()))
                 ui->comboMode->setCurrentIndex(RtlTextEditor);
         }
 
@@ -871,7 +871,7 @@ int EditDialog::checkDataType(const QByteArray& bArrdata)
         if(!json::parse(cellData, nullptr, false).is_discarded())
             return JSON;
         else {
-            if (QString::fromUtf8(cellData).isRightToLeft())
+            if (containsRightToLeft(QString::fromUtf8(cellData)))
                 return RtlText;
             else
                 return Text;