Fixed Selector.ValidateNestingSelector not calling overrides

Changed ValidateNestingSelector to call recursively walking up
the hierarchy of parent selectors. This means function overrides
are taken into account when walking up the tree. Now if a leaf
selector has an OrSelector as its parent, the OrSelector doesn't
throw an exception.

Author: zacfromaustinpowder

src/Avalonia.Base/Styling/OrSelector.cs

@@ -97,13 +97,13 @@ private protected override SelectorMatch Evaluate(StyledElement control, IStyle?
         private protected override Selector? MovePrevious() => null;
         private protected override Selector? MovePreviousOrParent() => null;
 
-        internal override void ValidateNestingSelector(bool inControlTheme)
+        internal override void ValidateNestingSelector(bool inControlTheme, int templateCount = 0)
         {
             var count = _selectors.Count;
 
             for (var i = 0; i < count; i++)
             {
-                _selectors[i].ValidateNestingSelector(inControlTheme);
+                _selectors[i].ValidateNestingSelector(inControlTheme, templateCount);
             }
         }
 

src/Avalonia.Base/Styling/Selector.cs

@@ -100,30 +100,31 @@ internal SelectorMatch Match(StyledElement control, IStyle? parent = null, bool
         /// </summary>
         private protected abstract Selector? MovePreviousOrParent();
 
-        internal virtual void ValidateNestingSelector(bool inControlTheme)
+        internal virtual void ValidateNestingSelector(bool inControlTheme, int templateCount = 0)
         {
             var s = this;
-            var templateCount = 0;
 
-            do
+            if (inControlTheme)
             {
-                if (inControlTheme)
-                {
-                    if (!s.InTemplate && s.IsCombinator)
-                        throw new InvalidOperationException(
-                            "ControlTheme style may not directly contain a child or descendent selector.");
-                    if (s is TemplateSelector && templateCount++ > 0)
-                        throw new InvalidOperationException(
-                            "ControlTemplate styles cannot contain multiple template selectors.");
-                }
-
-                var previous = s.MovePreviousOrParent();
+                if (!s.InTemplate && s.IsCombinator)
+                    throw new InvalidOperationException(
+                        "ControlTheme style may not directly contain a child or descendent selector.");
+                if (s is TemplateSelector && templateCount++ > 0)
+                    throw new InvalidOperationException(
+                        "ControlTemplate styles cannot contain multiple template selectors.");
+            }
+            
+            var previous = s.MovePreviousOrParent();
 
-                if (previous is null && s is not NestingSelector)
+            if (previous is null)
+            {
+                if (s is not NestingSelector)
                     throw new InvalidOperationException("Child styles must have a nesting selector.");
-
-                s = previous;
-            } while (s is not null);
+            }
+            else
+            {
+                previous.ValidateNestingSelector(inControlTheme, templateCount);
+            }
         }
 
         private static SelectorMatch MatchUntilCombinator(

tests/Avalonia.Base.UnitTests/Styling/SelectorTests_Or.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Controls;
 using Avalonia.Styling;
 using Xunit;
@@ -89,6 +90,24 @@ public void Returns_Null_TargetType_When_A_Selector_Has_No_TargetType()
 
             Assert.Equal(null, target.TargetType);
         }
+        
+        [Fact]
+        public void ValidateNestingSelector_Checks_Children_When_Parent_Is_An_OrSelector()
+        {
+            var target = Selectors.Or(
+                default(Selector).Class("foo"),
+                default(Selector).Class("bar")
+            ).Name("baz");
+
+            Assert.Throws<InvalidOperationException>(() => target.ValidateNestingSelector(false));
+            
+            target = Selectors.Or(
+                default(Selector).Nesting().Class("foo"),
+                default(Selector).Nesting().Class("bar")
+            ).Name("baz");
+            
+            target.ValidateNestingSelector(false);
+        }
 
         public class Control1 : Control
         {