[X] GetValueSource

first pass on a GetSourceValue API

Author: StephaneDelcroix

src/Controls/src/Core/Xaml/Diagnostics/BindablePropertyDiagnostics.cs

@@ -0,0 +1,82 @@
+using System;
+
+namespace Microsoft.Maui.Controls.Xaml.Diagnostics;
+
+internal static class BindablePropertyDiagnostics
+{
+    public static ValueSource GetValueSource(BindableObject bindable, BindableProperty property)
+    {
+        if (bindable == null)
+            throw new ArgumentNullException(nameof(bindable));
+        if (property == null)
+            throw new ArgumentNullException(nameof(property));
+
+        var context = bindable.GetContext(property);
+        if (context == null)
+            return new ValueSource(BaseValueSource.Unknown);  
+
+        var specificity = context.Values.GetSpecificityAndValue().Key;
+        if (specificity == SetterSpecificity.DefaultValue)
+            return new ValueSource(BaseValueSource.Default);
+        if (specificity == SetterSpecificity.FromBinding)
+            return new ValueSource(BaseValueSource.Unknown, isExpression:true);
+        if (specificity == SetterSpecificity.ManualValueSetter)
+            return new ValueSource(BaseValueSource.Local);
+        if (specificity == SetterSpecificity.DynamicResourceSetter)
+            return new ValueSource(BaseValueSource.Unknown, isExpression:true);
+        if (specificity == SetterSpecificity.VisualStateSetter)
+            return new ValueSource(BaseValueSource.Style);
+        if (specificity == SetterSpecificity.Trigger)
+            return new ValueSource(BaseValueSource.StyleTrigger);
+        if (specificity == SetterSpecificity.FromHandler)
+            return new ValueSource(BaseValueSource.Unknown, isCurrent:true);
+        
+        if (specificity.Vsm > 0)
+            return new ValueSource(BaseValueSource.Local);
+        if (specificity.Style > 0)
+            return new ValueSource(BaseValueSource.Style);
+        if (specificity.Id > 0 || specificity.Class > 0 || specificity.Type > 0)    
+            return new ValueSource(BaseValueSource.Style);
+        if (specificity.Manual > 0) 
+            return new ValueSource(BaseValueSource.Local);
+        if (specificity.DynamicResource > 0)
+            return new ValueSource(BaseValueSource.Unknown, isExpression:true);
+        if (specificity.Binding > 0)    
+            return new ValueSource(BaseValueSource.Unknown, isExpression:true);
+        
+        return new ValueSource(BaseValueSource.Unknown);
+    }
+}
+
+internal struct ValueSource {
+	public ValueSource(BaseValueSource baseValueSource, bool isCoerced =false, bool isCurrent=false, bool isExpression=false) 
+	{
+		BaseValueSource = baseValueSource;
+        IsCoerced = isCoerced;
+        IsCurrent = isCurrent;
+        IsExpression = isExpression;
+	}
+
+	public BaseValueSource BaseValueSource { get; }
+    public bool IsCoerced { get; }  
+    public bool IsCurrent { get; } //FromHandler
+    public bool IsExpression { get; }   //Binding, DynamicResource, etc
+	public BaseValueSource Unknown { get; }
+}
+
+internal enum BaseValueSource
+{
+    Unknown = 0, //source is not known
+    Default = 1, //source is default value, as defined by BindableProperty.DefaultValue or created by BindableProperty.DefaultValueCreator
+    Inherited = 2, //source is a value through property value inheritance (not really supported in Maui)
+    DefaultStyle = 3,
+    DefaultStyleTrigger = 4,
+    Style = 5,
+    TemplateTrigger = 6,
+    StyleTrigger = 7,
+    ImplicitStyleReference = 8,
+    ParentTemplate = 9,
+    ParentTemplateTrigger = 10,
+    Local = 11,
+    
+}