[expression] fix format_number() not adding group separators regression

Author: nirvn

src/core/expression/qgsexpressionfunction.cpp

@@ -3072,7 +3072,9 @@ static QVariant fcnFormatNumber( const QVariantList &values, const QgsExpression
     parent->setEvalErrorString( QObject::tr( "Number of places must be positive" ) );
     return QVariant();
   }
-  return QStringLiteral( "%L1" ).arg( value, 0, 'f', places );
+  QLocale locale = QLocale();
+  locale.setNumberOptions( locale.numberOptions() &= ~QLocale::NumberOption::OmitGroupSeparator );
+  return locale.toString( value, 'f', places );
 }
 
 static QVariant fcnFormatDate( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )

tests/src/core/testqgsexpression.cpp

@@ -1011,6 +1011,10 @@ class TestQgsExpression: public QObject
       QTest::newRow( "flip_coordinates point" ) << "geom_to_wkt(flip_coordinates(geom_from_wkt('POINT(1 2)')))" << false << QVariant( "Point (2 1)" );
 
       // string functions
+      QTest::newRow( "format_number" ) << "format_number(1999.567,2)" << false << QVariant( "1,999.57" );
+      QTest::newRow( "format_number large" ) << "format_number(9000000.0,0)" << false << QVariant( "9,000,000" );
+      QTest::newRow( "format_number many decimals" ) << "format_number(123.45600,4)" << false << QVariant( "123.4560" );
+      QTest::newRow( "format_number no decimals" ) << "format_number(1999.567,0)" << false << QVariant( "2,000" );
       QTest::newRow( "lower" ) << "lower('HeLLo')" << false << QVariant( "hello" );
       QTest::newRow( "upper" ) << "upper('HeLLo')" << false << QVariant( "HELLO" );
       QTest::newRow( "length" ) << "length('HeLLo')" << false << QVariant( 5 );