layout: fix dimensions of empty list

When the Min constraints are set but the list
has no item to display, use those as the list
returned dimensions.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

layout/list.go

@@ -293,6 +293,11 @@ func (l *List) layout(ops *op.Ops, macro op.MacroOp) Dimensions {
 	if pos > mainMax {
 		pos = mainMax
 	}
+	if crossMin, crossMax := l.Axis.crossConstraint(l.cs); maxCross < crossMin {
+		maxCross = crossMin
+	} else if maxCross > crossMax {
+		maxCross = crossMax
+	}
 	dims := l.Axis.Convert(image.Pt(pos, maxCross))
 	call := macro.Stop()
 	defer clip.Rect(image.Rectangle{Max: dims}).Push(ops).Pop()

layout/list_test.go

@@ -13,6 +13,18 @@ import (
 	"gioui.org/op"
 )
 
+func TestEmptyList(t *testing.T) {
+	var l List
+	gtx := Context{
+		Ops:         new(op.Ops),
+		Constraints: Exact(image.Pt(20, 10)),
+	}
+	dims := l.Layout(gtx, 0, nil)
+	if got, want := dims.Size, gtx.Constraints.Min; got != want {
+		t.Errorf("got %v; want %v", got, want)
+	}
+}
+
 func TestListPosition(t *testing.T) {
 	_s := func(e ...event.Event) []event.Event { return e }
 	r := new(router.Router)