Fix OnPlatform + Setter when no match for current platform (#17061)

* Fix OnPlatform + Setter when no match for current platform

When OnPlatforfm is used for a Setter value, and there's no match for the
current platform, fix so that the property isn't set (same behavior as Xamarin.Forms).
Previously, XamlC would report a "Missing Value For Setter" error when this happens
and non-compiled XAML would crash with an NRE. This PR contains fixes for both,
ensuring the XAML compiler doesn't show an error, then ensuring it doesn't crash
at runtime.

Fixes #12064

* Swtich to device tests for OnPlatform

* Remove test screenshot, no longer used

src/Controls/src/Build.Tasks/CompiledValueProviders/SetterValueProvider.cs

@@ -23,8 +23,9 @@ public IEnumerable<Instruction> ProvideValue(VariableDefinitionReference vardefr
 			if (SetterValueIsCollection(bpRef, module, node, context))
 				yield break;
 
+			// valueNode is null, for example, when OnPlatform doesn't have a match for the current platform, so the property should not be set
 			if (valueNode == null)
-				throw new XamlParseException("Missing Value for Setter", (IXmlLineInfo)node);
+				yield break;
 
 			//if it's an elementNode, there's probably no need to convert it
 			if (valueNode is IElementNode)

src/Controls/src/Xaml/MarkupExtensions/OnPlatformExtension.cs

@@ -65,7 +65,13 @@ public object ProvideValue(IServiceProvider serviceProvider)
 			if (!TryGetValueForPlatform(out var value))
 			{
 				if (bp != null)
-					return bp.GetDefaultValue(valueProvider.TargetObject as BindableObject);
+				{
+					object targetObject = valueProvider.TargetObject;
+
+					if (targetObject is Setter)
+						return null;
+					else return bp.GetDefaultValue(targetObject as BindableObject);
+				}
 				if (propertyType.IsValueType)
 					return Activator.CreateInstance(propertyType);
 				return null;

src/Controls/tests/Xaml.UnitTests/OnPlatform.xaml

@@ -21,7 +21,16 @@
 			<OnIdiom x:Key="fontSize" x:TypeArguments="x:Double"
 				Phone="{StaticResource phone}"
 				Tablet="{StaticResource tablet}"/>
-
+            <Style x:Key="ButtonStyle0" TargetType="Button">
+                <Setter Property="FontSize" Value="{OnPlatform iOS=36}" />
+            </Style>
+            <Style x:Key="ButtonStyle1" TargetType="Button">
+                <Setter Property="FontSize">
+                    <OnPlatform x:TypeArguments="x:Double">
+                        <On Platform="iOS">36</On>
+                    </OnPlatform>
+                </Setter>
+            </Style>
 		</ResourceDictionary>
 	</ContentPage.Resources>
 	<StackLayout>
@@ -51,5 +60,8 @@
 				</OnPlatform>
 			</Label.HeightRequest>
 		</Label>
+        <Button x:Name="button0" Style="{StaticResource ButtonStyle0}" Text="Button label" />
+        <Button x:Name="button1" Style="{StaticResource ButtonStyle1}" Text="Button label" />
+        <Button x:Name="button2" FontSize="{OnPlatform iOS=36}" Text="Button label" />
 	</StackLayout>
 </ContentPage>

src/Controls/tests/Xaml.UnitTests/OnPlatform.xaml.cs

@@ -61,6 +61,10 @@ public void DoubleToWidth(bool useCompiledXaml)
 				mockDeviceInfo.Platform = DevicePlatform.Android;
 				layout = new OnPlatform(useCompiledXaml);
 				Assert.AreEqual(30, layout.label0.WidthRequest);
+
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(0.0, layout.label0.WidthRequest);
 			}
 
 			[TestCase(false)]
@@ -74,6 +78,10 @@ public void StringToText(bool useCompiledXaml)
 				mockDeviceInfo.Platform = DevicePlatform.Android;
 				layout = new OnPlatform(useCompiledXaml);
 				Assert.AreEqual("Bar", layout.label0.Text);
+
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(null, layout.label0.Text);
 			}
 
 			[TestCase(false)]
@@ -87,7 +95,8 @@ public void OnPlatformAsResource(bool useCompiledXaml)
 				Assert.AreEqual(FontAttributes.Bold, (FontAttributes)onplat);
 				mockDeviceInfo.Platform = DevicePlatform.Android;
 				Assert.AreEqual(FontAttributes.Italic, (FontAttributes)onplat);
-
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				Assert.AreEqual(FontAttributes.None, (FontAttributes)onplat);
 			}
 
 			[TestCase(false)]
@@ -119,6 +128,9 @@ public void OnPlatform2Syntax(bool useCompiledXaml)
 				layout = new OnPlatform(useCompiledXaml);
 				Assert.AreEqual(21, layout.label0.HeightRequest);
 
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(63.0, layout.label0.HeightRequest);
 
 				mockDeviceInfo.Platform = DevicePlatform.Create("FooBar");
 				layout = new OnPlatform(useCompiledXaml);
@@ -133,6 +145,45 @@ public void OnPlatformDefault(bool useCompiledXaml)
 				var layout = new OnPlatform(useCompiledXaml);
 				Assert.AreEqual(63, layout.label0.HeightRequest);
 			}
+
+			[TestCase(false)]
+			[TestCase(true)]
+			public void OnPlatformInStyle0(bool useCompiledXaml)
+			{
+				mockDeviceInfo.Platform = DevicePlatform.iOS;
+				var layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(36, layout.button0.FontSize);
+
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(0.0, layout.button0.FontSize);
+			}
+
+			[TestCase(false)]
+			[TestCase(true)]
+			public void OnPlatformInStyle1(bool useCompiledXaml)
+			{
+				mockDeviceInfo.Platform = DevicePlatform.iOS;
+				var layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(36, layout.button1.FontSize);
+
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(0.0, layout.button1.FontSize);
+			}
+
+			[TestCase(false)]
+			[TestCase(true)]
+			public void OnPlatformInline(bool useCompiledXaml)
+			{
+				mockDeviceInfo.Platform = DevicePlatform.iOS;
+				var layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(36, layout.button2.FontSize);
+
+				mockDeviceInfo.Platform = DevicePlatform.MacCatalyst;
+				layout = new OnPlatform(useCompiledXaml);
+				Assert.AreEqual(0.0, layout.button2.FontSize);
+			}
 		}
 	}
 }