Let the Grid skip * measurements during the first pass if they'll be …

…overwritten later (#13523)

Co-authored-by: E.Z. Hart <hartez@gmail.com>

src/Core/src/Layouts/GridLayoutManager.cs

@@ -336,7 +336,7 @@ static double SumDefinitions(Definition[] definitions, double spacing)
 
 			void MeasureCells()
 			{
-				AutoMeasurePass();
+                KnownMeasurePass();
 
 				if (!_isStarWidthPrecomputable)
 				{
@@ -367,49 +367,59 @@ Size MeasureCell(Cell cell, double width, double height)
 				return result;
 			}
 
-			void AutoMeasurePass()
-			{
-				for (int n = 0; n < _cells.Length; n++)
-				{
-					var cell = _cells[n];
-
-					if (double.IsNaN(cell.MeasureHeight) || double.IsNaN(cell.MeasureWidth))
-					{
-						cell.NeedsSecondPass = true;
-					}
-
-					var measureWidth = double.IsNaN(cell.MeasureWidth) ? double.PositiveInfinity : cell.MeasureWidth;
-					var measureHeight = double.IsNaN(cell.MeasureHeight) ? double.PositiveInfinity : cell.MeasureHeight;
-
-					var measure = MeasureCell(cell, measureWidth, measureHeight);
-
-					if (cell.IsColumnSpanAuto)
-					{
-						if (cell.ColumnSpan == 1)
-						{
-							_columns[cell.Column].Update(measure.Width);
-						}
-						else
-						{
-							TrackSpan(new Span(cell.Column, cell.ColumnSpan, true, measure.Width));
-						}
-					}
-
-					if (cell.IsRowSpanAuto)
-					{
-						if (cell.RowSpan == 1)
-						{
-							_rows[cell.Row].Update(measure.Height);
-						}
-						else
-						{
-							TrackSpan(new Span(cell.Row, cell.RowSpan, false, measure.Height));
-						}
-					}
-				}
-			}
-
-			void SecondMeasurePass()
+            void KnownMeasurePass()
+            {
+                for (int n = 0; n < _cells.Length; n++)
+                {
+                    var cell = _cells[n];
+
+                    if (double.IsNaN(cell.MeasureHeight) || double.IsNaN(cell.MeasureWidth))
+                    {
+                        // We still have some unknown measure constraints (* rows/columns that need to have
+                        // the Auto measurements settled before we can measure them). So mark this cell for the 
+                        // second pass, once we know the constraints.
+                        cell.NeedsSecondPass = true;
+
+                        if (!cell.IsColumnSpanAuto && !cell.IsRowSpanAuto)
+                        {
+                            // If neither span of this cell includes _any_ Auto values, then there's no reason
+                            // to measure it at all during this pass; we can skip it for now
+                            continue;
+                        }
+                    }
+
+                    var measureWidth = double.IsNaN(cell.MeasureWidth) ? double.PositiveInfinity : cell.MeasureWidth;
+                    var measureHeight = double.IsNaN(cell.MeasureHeight) ? double.PositiveInfinity : cell.MeasureHeight;
+
+                    var measure = MeasureCell(cell, measureWidth, measureHeight);
+
+                    if (cell.IsColumnSpanAuto)
+                    {
+                        if (cell.ColumnSpan == 1)
+                        {
+                            _columns[cell.Column].Update(measure.Width);
+                        }
+                        else
+                        {
+                            TrackSpan(new Span(cell.Column, cell.ColumnSpan, true, measure.Width));
+                        }
+                    }
+
+                    if (cell.IsRowSpanAuto)
+                    {
+                        if (cell.RowSpan == 1)
+                        {
+                            _rows[cell.Row].Update(measure.Height);
+                        }
+                        else
+                        {
+                            TrackSpan(new Span(cell.Row, cell.RowSpan, false, measure.Height));
+                        }
+                    }
+                }
+            }
+
+            void SecondMeasurePass()
 			{
 				foreach (var cell in _cells)
 				{