[Spreadsheet] add visible alias check

as discussed in https://forum.freecadweb.org/viewtopic.php?p=408992#p408981
visible feedback is missing for the Alias field. This PR add it and also adapts the UI label style.

src/Mod/Spreadsheet/Gui/Sheet.ui

@@ -19,7 +19,7 @@
      <item row="0" column="0">
       <widget class="QLabel" name="label">
        <property name="text">
-        <string>&amp;Contents</string>
+        <string>&amp;Content:</string>
        </property>
        <property name="buddy">
         <cstring>cellContent</cstring>
@@ -36,7 +36,7 @@
      <item row="0" column="2">
       <widget class="QLabel" name="alias_label">
        <property name="text">
-        <string>&amp;Alias</string>
+        <string>&amp;Alias:</string>
        </property>
        <property name="buddy">
         <cstring>cellAlias</cstring>
@@ -49,9 +49,8 @@
         <bool>false</bool>
        </property>
        <property name="toolTip">
-       <string>Refer to cell by alias, for example
-Spreadsheet.my_alias_name instead of Spreadsheet.B1
-       </string>
+        <string>Refer to cell by alias, for example
+Spreadsheet.my_alias_name instead of Spreadsheet.B1</string>
        </property>
       </widget>
      </item>

src/Mod/Spreadsheet/Gui/SpreadsheetView.cpp

@@ -35,24 +35,24 @@
 # include <cmath>
 #endif
 
-#include "SpreadsheetView.h"
-#include "SpreadsheetDelegate.h"
-#include <Mod/Spreadsheet/App/Sheet.h>
+#include <App/DocumentObject.h>
+#include <App/PropertyStandard.h>
 #include <App/Range.h>
+#include <Base/Tools.h>
+#include <boost_bind_bind.hpp>
 #include <Gui/MainWindow.h>
 #include <Gui/Application.h>
+#include <Gui/Command.h>
 #include <Gui/CommandT.h>
 #include <Gui/Document.h>
 #include <Gui/ExpressionCompleter.h>
-#include <App/DocumentObject.h>
-#include <App/PropertyStandard.h>
-#include <Gui/Command.h>
-#include <boost_bind_bind.hpp>
+#include <LineEdit.h>
+#include <Mod/Spreadsheet/App/Sheet.h>
 #include <Mod/Spreadsheet/App/Utils.h>
 #include "qtcolorpicker.h"
-#include <LineEdit.h>
-#include <Base/Tools.h>
 
+#include "SpreadsheetView.h"
+#include "SpreadsheetDelegate.h"
 #include "ui_Sheet.h"
 
 using namespace SpreadsheetGui;
@@ -99,6 +99,7 @@ SheetView::SheetView(Gui::Document *pcDocument, App::DocumentObject *docObj, QWi
 
     connect(ui->cellContent, SIGNAL(returnPressed()), this, SLOT( editingFinished() ));
     connect(ui->cellAlias, SIGNAL(returnPressed()), this, SLOT( editingFinished() ));
+    connect(ui->cellAlias, SIGNAL(textEdited(QString)), this, SLOT(aliasChanged(QString)));
 
     columnWidthChangedConnection = sheet->columnWidthChanged.connect(bind(&SheetView::resizeColumn, this, bp::_1, bp::_2));
     rowHeightChangedConnection = sheet->rowHeightChanged.connect(bind(&SheetView::resizeRow, this, bp::_1, bp::_2));
@@ -370,6 +371,31 @@ void SheetView::editingFinished()
     }
 }
 
+void SheetView::aliasChanged(const QString& text)
+{
+    // check live the input and highlight if the user input invalid characters
+
+    bool aliasOk = true;
+    QPalette palette = ui->cellAlias->palette();
+
+    if (!text.isEmpty() && !sheet->isValidAlias(Base::Tools::toStdString(text)))
+        aliasOk = false;
+
+    if (!aliasOk) {
+        // change tooltip and make text color red
+        ui->cellAlias->setToolTip(QObject::tr("Alias contains invalid characters!"));
+        palette.setColor(QPalette::Text, Qt::red);
+    }
+    else {
+        // go back to normal
+        ui->cellAlias->setToolTip(
+            QObject::tr("Refer to cell by alias, for example\nSpreadsheet.my_alias_name instead of Spreadsheet.B1"));
+        palette.setColor(QPalette::Text, Qt::black);
+    }
+    // apply the text color via the palette
+    ui->cellAlias->setPalette(palette);
+}
+
 void SheetView::currentChanged ( const QModelIndex & current, const QModelIndex & previous  )
 {
     Q_UNUSED(current);

src/Mod/Spreadsheet/Gui/SpreadsheetView.h

@@ -83,6 +83,7 @@ public:
 
 protected Q_SLOTS:
     void editingFinished();
+    void aliasChanged(const QString& text);
     void currentChanged( const QModelIndex & current, const QModelIndex & previous );
     void columnResized(int col, int oldSize, int newSize);
     void rowResized(int row, int oldSize, int newSize);