Fix broken $x_at, $y_at functions (fix #14462), add tests

(cherry-picked from 3b40e2b)

Author: nyalldawson

src/core/qgsexpression.cpp

@@ -1597,17 +1597,22 @@ static QVariant pointAt( const QVariantList& values, const QgsExpressionContext*
 {
   FEAT_FROM_CONTEXT( context, f );
   int idx = getIntValue( values.at( 0 ), parent );
-  ENSURE_GEOM_TYPE( f, g, QGis::Line );
-  QgsPolyline polyline = g->asPolyline();
-  if ( idx < 0 )
-    idx += polyline.count();
+  const QgsGeometry* g = f.constGeometry();
+  if ( !g || g->isEmpty() )
+    return QVariant();
 
-  if ( idx < 0 || idx >= polyline.count() )
+  if ( idx < 0 )
+  {
+    idx += g->geometry()->nCoordinates();
+  }
+  if ( idx < 0 || idx >= g->geometry()->nCoordinates() )
   {
     parent->setEvalErrorString( QObject::tr( "Index is out of range" ) );
     return QVariant();
   }
-  return QVariant( QPointF( polyline[idx].x(), polyline[idx].y() ) );
+
+  QgsPoint p = g->vertexAt( idx );
+  return QVariant( QPointF( p.x(), p.y() ) );
 }
 
 static QVariant fcnXat( const QVariantList& values, const QgsExpressionContext* f, QgsExpression* parent )

src/core/qgsexpressionlexer.ll

@@ -106,6 +106,7 @@ col_first    [A-Za-z_]|{non_ascii}
 col_next     [A-Za-z0-9_]|{non_ascii}
 column_ref  {col_first}{col_next}*
 
+deprecated_function "$"[xXyY]_?[aA][tT]
 special_col "$"{column_ref}
 variable "@"{column_ref}
 
@@ -193,6 +194,8 @@ string      "'"{str_char}*"'"
 
 {string}  { TEXT_FILTER(stripText); return STRING; }
 
+{deprecated_function} { TEXT; return FUNCTION; }
+
 {special_col}        { TEXT; return SPECIAL_COL; }
 
 {variable}        { TEXT; return VARIABLE; }

tests/src/core/testqgsexpression.cpp

@@ -1243,10 +1243,65 @@ class TestQgsExpression: public QObject
       vPerimeter = exp3.evaluate( &context );
       QCOMPARE( vPerimeter.toDouble(), 26. );
 
+      QgsExpression deprecatedExpXAt( "$x_at(1)" );
+      context.setFeature( fPolygon );
+      QVariant xAt = deprecatedExpXAt.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 10.0 );
+      context.setFeature( fPolyline );
+      xAt = deprecatedExpXAt.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 10.0 );
+
+      QgsExpression deprecatedExpXAtNeg( "$x_at(-2)" );
+      context.setFeature( fPolygon );
+      xAt = deprecatedExpXAtNeg.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 2.0 );
+
+      QgsExpression deprecatedExpYAt( "$y_at(2)" );
+      context.setFeature( fPolygon );
+      QVariant yAt = deprecatedExpYAt.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 6.0 );
+      QgsExpression deprecatedExpYAt2( "$y_at(1)" );
+      context.setFeature( fPolyline );
+      yAt = deprecatedExpYAt2.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 0.0 );
+
+      QgsExpression deprecatedExpYAtNeg( "$y_at(-2)" );
+      context.setFeature( fPolygon );
+      yAt = deprecatedExpYAtNeg.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 6.0 );
+
+      QgsExpression expXAt( "x_at(1)" );
+      context.setFeature( fPolygon );
+      xAt = expXAt.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 10.0 );
+      context.setFeature( fPolyline );
+      xAt = expXAt.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 10.0 );
+
+      QgsExpression expXAtNeg( "x_at(-2)" );
+      context.setFeature( fPolygon );
+      xAt = expXAtNeg.evaluate( &context );
+      QCOMPARE( xAt.toDouble(), 2.0 );
+
+      QgsExpression expYAt( "y_at(2)" );
+      context.setFeature( fPolygon );
+      yAt = expYAt.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 6.0 );
+      QgsExpression expYAt2( "$y_at(1)" );
+      context.setFeature( fPolyline );
+      yAt = expYAt2.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 0.0 );
+
+      QgsExpression expYAtNeg( "y_at(-2)" );
+      context.setFeature( fPolygon );
+      yAt = expYAtNeg.evaluate( &context );
+      QCOMPARE( yAt.toDouble(), 6.0 );
+
       QgsExpression exp4( "bounds_width($geometry)" );
       QVariant vBoundsWidth = exp4.evaluate( &fPolygon );
       QCOMPARE( vBoundsWidth.toDouble(), 8.0 );
 
+      context.setFeature( fPolygon );
       vBoundsWidth = exp4.evaluate( &context );
       QCOMPARE( vBoundsWidth.toDouble(), 8.0 );