Fix 'nan'='nan' evaluates to false in expressions

Also fix 'nan' and 'inf' being treated as doubles rather than
strings.

src/core/qgsexpression.cpp

@@ -176,7 +176,13 @@ inline bool isDoubleSafe( const QVariant& v )
   if ( v.type() == QVariant::UInt ) return true;
   if ( v.type() == QVariant::LongLong ) return true;
   if ( v.type() == QVariant::ULongLong ) return true;
-  if ( v.type() == QVariant::String ) { bool ok; v.toString().toDouble( &ok ); return ok; }
+  if ( v.type() == QVariant::String )
+  {
+    bool ok;
+    double val = v.toString().toDouble( &ok );
+    ok = ok && qIsFinite( val ) && !qIsNaN( val );
+    return ok;
+  }
   return false;
 }
 
@@ -239,7 +245,7 @@ static double getDoubleValue( const QVariant& value, QgsExpression* parent )
 {
   bool ok;
   double x = value.toDouble( &ok );
-  if ( !ok )
+  if ( !ok || qIsNaN( x ) || !qIsFinite( x ) )
   {
     parent->setEvalErrorString( QObject::tr( "Cannot convert '%1' to double" ).arg( value.toString() ) );
     return 0;

tests/src/core/testqgsexpression.cpp

@@ -202,7 +202,10 @@ class TestQgsExpression: public QObject
       QTest::newRow( "plus double" ) << "1+1.3" << false << QVariant( 2.3 );
       QTest::newRow( "plus with null" ) << "null+3" << false << QVariant();
       QTest::newRow( "plus invalid" ) << "1+'foo'" << true << QVariant();
+
       QTest::newRow( "minus int" ) << "1-3" << false << QVariant( -2 );
+      QTest::newRow( "minus nan" ) << "1-'nan'" << true << QVariant();
+      QTest::newRow( "minus inf" ) << "1-'inf'" << true << QVariant();
       QTest::newRow( "mul int" ) << "8*7" << false << QVariant( 56 );
       QTest::newRow( "div int" ) << "5/2" << false << QVariant( 2.5 );
       QTest::newRow( "mod int" ) << "20%6" << false << QVariant( 2 );
@@ -238,6 +241,10 @@ class TestQgsExpression: public QObject
       QTest::newRow( "ge int 2" ) << "3 >= 3" << false << QVariant( 1 );
       QTest::newRow( "lt text 1" ) << "'bar' < 'foo'" << false << QVariant( 1 );
       QTest::newRow( "lt text 2" ) << "'foo' < 'bar'" << false << QVariant( 0 );
+      QTest::newRow( "'nan'='nan'" ) << "'nan'='nan'" << false << QVariant( 1 );
+      QTest::newRow( "'nan'='x'" ) << "'nan'='x'" << false << QVariant( 0 );
+      QTest::newRow( "'inf'='inf'" ) << "'inf'='inf'" << false << QVariant( 1 );
+      QTest::newRow( "'inf'='x'" ) << "'inf'='x'" << false << QVariant( 0 );
 
       // is, is not
       QTest::newRow( "is null,null" ) << "null is null" << false << QVariant( 1 );