From 180410e076632dcc63579c8b9a4bad38e7e6aa12 Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Fri, 23 Feb 2024 20:13:52 -0800
Subject: [PATCH] TemplatePart XAML diagnostics (#14180)

* Add TemplatePart.IsRequired property and make attribute inherited

* Implement TemplatePart XAML diagnostics + tests

* Fix new errors in our XAML files

* Ignore nested metadata scopes in TemplatePart validator

* Update docs comment
---
 .editorconfig                                 |   6 +
 .../TransitioningContentControlPage.axaml     |   6 +-
 .../Metadata/TemplatePartAttribute.cs         |   9 +-
 .../Themes/Fluent.xaml                        |   3 +-
 .../Themes/Simple.xaml                        |   3 +-
 .../Chrome/CaptionButtons.cs                  |  33 +++--
 src/Avalonia.Controls/Chrome/TitleBar.cs      |   2 +-
 src/Avalonia.Controls/ComboBox.cs             |   2 +-
 .../DateTimePickers/DatePickerPresenter.cs    |  16 +--
 .../DateTimePickers/TimePickerPresenter.cs    |  14 +-
 .../NumericUpDown/NumericUpDown.cs            |   2 +-
 .../Primitives/HeaderedItemsControl.cs        |   2 +
 src/Avalonia.Controls/ProgressBar.cs          |   2 +-
 src/Avalonia.Controls/Slider.cs               |   9 +-
 src/Avalonia.Controls/TabControl.cs           |   1 +
 src/Avalonia.Controls/TextBox.cs              |   2 +-
 src/Avalonia.Controls/ToggleSwitch.cs         |   2 +-
 src/Avalonia.Dialogs/ManagedFileChooser.cs    |   4 +-
 .../Controls/CalendarButton.xaml              |   2 +-
 .../Controls/CalendarDayButton.xaml           |  12 +-
 .../Controls/CalendarItem.xaml                |   2 +-
 .../Controls/CheckBox.xaml                    |   2 +-
 .../Controls/DateTimePickerShared.xaml        |   2 +-
 .../Controls/FlyoutPresenter.xaml             |   3 +-
 .../Controls/NotificationCard.xaml            |   2 +-
 .../Controls/ScrollBar.xaml                   |   3 +-
 .../Controls/CalendarButton.xaml              |   2 +-
 .../Controls/CalendarDayButton.xaml           |  18 +--
 .../Controls/DateTimePickerShared.xaml        |   2 +-
 .../Controls/FlyoutPresenter.xaml             |   3 +-
 .../Controls/NotificationCard.xaml            |  13 +-
 .../AvaloniaXamlIlRuntimeCompiler.cs          |  19 ++-
 .../AvaloniaXamlDiagnosticCodes.cs            |   3 +
 .../AvaloniaXamlIlCompiler.cs                 |   1 +
 ...aloniaXamlIlControlTemplatePartsChecker.cs | 136 ++++++++++++++++++
 ...amlIlControlTemplatePriorityTransformer.cs |  11 +-
 ...olTemplateTargetTypeMetadataTransformer.cs |   2 +-
 .../AvaloniaXamlIlWellKnownTypes.cs           |   2 +
 .../RuntimeXamlLoaderConfiguration.cs         |  13 +-
 .../Xaml/ControlTemplateTests.cs              | 114 ++++++++++++++-
 40 files changed, 388 insertions(+), 97 deletions(-)
 create mode 100644 src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePartsChecker.cs

diff --git a/.editorconfig b/.editorconfig
index d5b2badfd5..ee24c310c0 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -212,6 +212,12 @@ indent_size = 2
 avalonia_xaml_diagnostic.AVLN2203.severity = error
 # StyleInMergedDictionaries
 avalonia_xaml_diagnostic.AVLN2204.severity = error
+# RequiredTemplatePartMissing
+avalonia_xaml_diagnostic.AVLN2205.severity = error
+# OptionalTemplatePartMissing
+avalonia_xaml_diagnostic.AVLN2206.severity = info
+# TemplatePartWrongType
+avalonia_xaml_diagnostic.AVLN2207.severity = error
 # Obsolete
 avalonia_xaml_diagnostic.AVLN5001.severity = error
 
diff --git a/samples/ControlCatalog/Pages/TransitioningContentControlPage.axaml b/samples/ControlCatalog/Pages/TransitioningContentControlPage.axaml
index 541385dd9f..03ef86fb61 100644
--- a/samples/ControlCatalog/Pages/TransitioningContentControlPage.axaml
+++ b/samples/ControlCatalog/Pages/TransitioningContentControlPage.axaml
@@ -23,10 +23,12 @@
                                 <ColumnDefinition Width="Auto" SharedSizeGroup="HeaderCol" />
                                 <ColumnDefinition Width="*" />
                             </Grid.ColumnDefinitions>
-                            <ContentPresenter Content="{TemplateBinding Header}" 
+                            <ContentPresenter x:Name="PART_HeaderPresenter"
+                                              Content="{TemplateBinding Header}" 
                                               Grid.Column="0" 
                                               VerticalAlignment="Center" />
-                            <ContentPresenter Content="{TemplateBinding Content}" 
+                            <ContentPresenter x:Name="PART_ContentPresenter"
+                                              Content="{TemplateBinding Content}" 
                                               Grid.Column="1" 
                                               VerticalAlignment="Center" />
                         </Grid>
diff --git a/src/Avalonia.Base/Controls/Metadata/TemplatePartAttribute.cs b/src/Avalonia.Base/Controls/Metadata/TemplatePartAttribute.cs
index 3b8f971713..a2a7e70946 100644
--- a/src/Avalonia.Base/Controls/Metadata/TemplatePartAttribute.cs
+++ b/src/Avalonia.Base/Controls/Metadata/TemplatePartAttribute.cs
@@ -5,8 +5,6 @@
 
 using System;
 
-#nullable enable
-
 namespace Avalonia.Controls.Metadata
 {
     /// <summary>
@@ -17,7 +15,7 @@ namespace Avalonia.Controls.Metadata
     /// Style authors should be able to identify the part type used for styling the specific control.
     /// The part is usually required in the style and should have a specific predefined name.
     /// </remarks>
-    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
     public sealed class TemplatePartAttribute : Attribute
     {
         /// <summary>
@@ -51,5 +49,10 @@ namespace Avalonia.Controls.Metadata
         /// in <see cref="Name"/>.
         /// </summary>
         public Type Type { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the template part is mandatory to be present in the template.
+        /// </summary>
+        public bool IsRequired { get; set; }
     }
 }
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
index 03a692f866..0825feb1a7 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml
@@ -183,7 +183,8 @@
                     <ColumnDefinition Width="Auto" MinWidth="{DynamicResource DataGridSortIconMinWidth}" />
                   </Grid.ColumnDefinitions>
                 
-                  <ContentPresenter Content="{TemplateBinding Content}"
+                  <ContentPresenter x:Name="PART_ContentPresenter"
+                                    Content="{TemplateBinding Content}"
                                     ContentTemplate="{TemplateBinding ContentTemplate}" />
                 
                   <Path Name="SortIcon"
diff --git a/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml b/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
index 71eb1df41f..1d77161bfb 100644
--- a/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
+++ b/src/Avalonia.Controls.DataGrid/Themes/Simple.xaml
@@ -66,7 +66,8 @@
                     HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                     VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                     ColumnDefinitions="*,Auto">
-                <ContentPresenter Content="{TemplateBinding Content}"
+                <ContentPresenter x:Name="PART_ContentPresenter"
+                                  Content="{TemplateBinding Content}"
                                   ContentTemplate="{TemplateBinding ContentTemplate}" />
 
                 <Path Name="SortIcon"
diff --git a/src/Avalonia.Controls/Chrome/CaptionButtons.cs b/src/Avalonia.Controls/Chrome/CaptionButtons.cs
index 237fa87968..82f4d16bfe 100644
--- a/src/Avalonia.Controls/Chrome/CaptionButtons.cs
+++ b/src/Avalonia.Controls/Chrome/CaptionButtons.cs
@@ -99,19 +99,28 @@ namespace Avalonia.Controls.Chrome
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
             base.OnApplyTemplate(e);
+            
+            if (e.NameScope.Find<Button>(PART_CloseButton) is { } closeButton)
+            {
+                closeButton.Click += (sender, e) => OnClose();
+            }
 
-            var closeButton = e.NameScope.Get<Button>(PART_CloseButton);
-            var restoreButton = e.NameScope.Get<Button>(PART_RestoreButton);
-            var minimizeButton = e.NameScope.Get<Button>(PART_MinimizeButton);
-            var fullScreenButton = e.NameScope.Get<Button>(PART_FullScreenButton);
-
-            closeButton.Click += (sender, e) => OnClose();
-            restoreButton.Click += (sender, e) => OnRestore();
-            minimizeButton.Click += (sender, e) => OnMinimize();
-            fullScreenButton.Click += (sender, e) => OnToggleFullScreen();
-
-            restoreButton.IsEnabled = HostWindow?.CanResize ?? true;
-            _restoreButton = restoreButton;
+            if (e.NameScope.Find<Button>(PART_RestoreButton) is { } restoreButton)
+            {
+                restoreButton.Click += (sender, e) => OnRestore();
+                restoreButton.IsEnabled = HostWindow?.CanResize ?? true;
+                _restoreButton = restoreButton;
+            }
+            
+            if (e.NameScope.Find<Button>(PART_MinimizeButton) is { } minimizeButton)
+            {
+                minimizeButton.Click += (sender, e) => OnMinimize();
+            }
+            
+            if (e.NameScope.Find<Button>(PART_FullScreenButton) is { } fullScreenButton)
+            {
+                fullScreenButton.Click += (sender, e) => OnToggleFullScreen();
+            }
         }
     }
 }
diff --git a/src/Avalonia.Controls/Chrome/TitleBar.cs b/src/Avalonia.Controls/Chrome/TitleBar.cs
index 368c9d4c2f..498f9cdf7f 100644
--- a/src/Avalonia.Controls/Chrome/TitleBar.cs
+++ b/src/Avalonia.Controls/Chrome/TitleBar.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Controls.Chrome
     /// <summary>
     /// Draws a titlebar when managed client decorations are enabled.
     /// </summary>
-    [TemplatePart("PART_CaptionButtons", typeof(CaptionButtons))]
+    [TemplatePart("PART_CaptionButtons", typeof(CaptionButtons), IsRequired = true)]
     [PseudoClasses(":minimized", ":normal", ":maximized", ":fullscreen")]
     public class TitleBar : TemplatedControl
     {
diff --git a/src/Avalonia.Controls/ComboBox.cs b/src/Avalonia.Controls/ComboBox.cs
index f33455f840..78bb191e93 100644
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@@ -17,7 +17,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A drop-down list control.
     /// </summary>
-    [TemplatePart("PART_Popup", typeof(Popup))]
+    [TemplatePart("PART_Popup", typeof(Popup), IsRequired = true)]
     [PseudoClasses(pcDropdownOpen, pcPressed)]
     public class ComboBox : SelectingItemsControl
     {
diff --git a/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs b/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
index 8ff8088a34..1c72509168 100644
--- a/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
+++ b/src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs
@@ -13,22 +13,22 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a date for a 
     /// <see cref="DatePicker"/>
     /// </summary>
-    [TemplatePart("PART_AcceptButton",    typeof(Button))]
+    [TemplatePart("PART_AcceptButton",    typeof(Button), IsRequired = true)]
     [TemplatePart("PART_DayDownButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_DayHost",         typeof(Panel))]
-    [TemplatePart("PART_DaySelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_DayHost",         typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_DaySelector",     typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_DayUpButton",     typeof(RepeatButton))]
     [TemplatePart("PART_DismissButton",   typeof(Button))]
     [TemplatePart("PART_FirstSpacer",     typeof(Rectangle))]
     [TemplatePart("PART_MonthDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_MonthHost",       typeof(Panel))]
-    [TemplatePart("PART_MonthSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MonthHost",       typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_MonthSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_MonthUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_PickerContainer", typeof(Grid))]
+    [TemplatePart("PART_PickerContainer", typeof(Grid), IsRequired = true)]
     [TemplatePart("PART_SecondSpacer",    typeof(Rectangle))]
     [TemplatePart("PART_YearDownButton",  typeof(RepeatButton))]
-    [TemplatePart("PART_YearHost",        typeof(Panel))]
-    [TemplatePart("PART_YearSelector",    typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_YearHost",        typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_YearSelector",    typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_YearUpButton",    typeof(RepeatButton))]
     public class DatePickerPresenter : PickerPresenterBase
     {
diff --git a/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs b/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
index 929ad68c24..7f19d0545e 100644
--- a/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
+++ b/src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs
@@ -11,20 +11,20 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a time. Intended for use with
     /// <see cref="TimePicker"/> but can be used independently
     /// </summary>
-    [TemplatePart("PART_AcceptButton",     typeof(Button))]
+    [TemplatePart("PART_AcceptButton",     typeof(Button), IsRequired = true)]
     [TemplatePart("PART_DismissButton",    typeof(Button))]
     [TemplatePart("PART_HourDownButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_HourSelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_HourSelector",     typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_HourUpButton",     typeof(RepeatButton))]
     [TemplatePart("PART_MinuteDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_MinuteSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MinuteSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_MinuteUpButton",   typeof(RepeatButton))]
     [TemplatePart("PART_PeriodDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_PeriodHost",       typeof(Panel))]
-    [TemplatePart("PART_PeriodSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_PeriodHost",       typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_PeriodSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_PeriodUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_PickerContainer",  typeof(Grid))]
-    [TemplatePart("PART_SecondSpacer",     typeof(Rectangle))]
+    [TemplatePart("PART_PickerContainer",  typeof(Grid), IsRequired = true)]
+    [TemplatePart("PART_SecondSpacer",     typeof(Rectangle), IsRequired = true)]
     public class TimePickerPresenter : PickerPresenterBase
     {
         /// <summary>
diff --git a/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs b/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
index 25d4a90a9d..0edc798494 100644
--- a/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
+++ b/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Controls
     /// Control that represents a TextBox with button spinners that allow incrementing and decrementing numeric values.
     /// </summary>
     [TemplatePart("PART_Spinner", typeof(Spinner))]
-    [TemplatePart("PART_TextBox", typeof(TextBox))]
+    [TemplatePart("PART_TextBox", typeof(TextBox), IsRequired = true)]
     public class NumericUpDown : TemplatedControl
     {
         /// <summary>
diff --git a/src/Avalonia.Controls/Primitives/HeaderedItemsControl.cs b/src/Avalonia.Controls/Primitives/HeaderedItemsControl.cs
index ad4d3324bb..a95280e640 100644
--- a/src/Avalonia.Controls/Primitives/HeaderedItemsControl.cs
+++ b/src/Avalonia.Controls/Primitives/HeaderedItemsControl.cs
@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Collections;
+using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
@@ -10,6 +11,7 @@ namespace Avalonia.Controls.Primitives
     /// <summary>
     /// Represents an <see cref="ItemsControl"/> with a related header.
     /// </summary>
+    [TemplatePart("PART_HeaderPresenter", typeof(ContentPresenter))]
     public class HeaderedItemsControl : ItemsControl, IContentPresenterHost
     {
         private IDisposable? _itemsBinding;
diff --git a/src/Avalonia.Controls/ProgressBar.cs b/src/Avalonia.Controls/ProgressBar.cs
index 193ed052d4..220931b4f4 100644
--- a/src/Avalonia.Controls/ProgressBar.cs
+++ b/src/Avalonia.Controls/ProgressBar.cs
@@ -13,7 +13,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control used to indicate the progress of an operation.
     /// </summary>
-    [TemplatePart("PART_Indicator", typeof(Border))]
+    [TemplatePart("PART_Indicator", typeof(Border), IsRequired = true)]
     [PseudoClasses(":vertical", ":horizontal", ":indeterminate")]
     public class ProgressBar : RangeBase
     {
diff --git a/src/Avalonia.Controls/Slider.cs b/src/Avalonia.Controls/Slider.cs
index 6fbfd6f41b..ccb1124e63 100644
--- a/src/Avalonia.Controls/Slider.cs
+++ b/src/Avalonia.Controls/Slider.cs
@@ -45,7 +45,7 @@ namespace Avalonia.Controls
     /// </summary>
     [TemplatePart("PART_DecreaseButton", typeof(Button))]
     [TemplatePart("PART_IncreaseButton", typeof(Button))]
-    [TemplatePart("PART_Track",          typeof(Track))]
+    [TemplatePart("PART_Track",          typeof(Track), IsRequired = true)]
     [PseudoClasses(":vertical", ":horizontal", ":pressed")]
     public class Slider : RangeBase
     {
@@ -204,13 +204,10 @@ namespace Avalonia.Controls
             _pointerMovedDispose?.Dispose();
 
             _decreaseButton = e.NameScope.Find<Button>("PART_DecreaseButton");
-            _track = e.NameScope.Find<Track>("PART_Track");
+            _track = e.NameScope.Get<Track>("PART_Track");
             _increaseButton = e.NameScope.Find<Button>("PART_IncreaseButton");
 
-            if (_track != null)
-            {
-                _track.IgnoreThumbDrag = true;
-            }
+            _track.IgnoreThumbDrag = true;
 
             if (_decreaseButton != null)
             {
diff --git a/src/Avalonia.Controls/TabControl.cs b/src/Avalonia.Controls/TabControl.cs
index e71a5a656b..40c10fe29f 100644
--- a/src/Avalonia.Controls/TabControl.cs
+++ b/src/Avalonia.Controls/TabControl.cs
@@ -18,6 +18,7 @@ namespace Avalonia.Controls
     /// A tab control that displays a tab strip along with the content of the selected tab.
     /// </summary>
     [TemplatePart("PART_ItemsPresenter", typeof(ItemsPresenter))]
+    [TemplatePart("PART_SelectedContentHost", typeof(ContentPresenter))]
     public class TabControl : SelectingItemsControl, IContentPresenterHost
     {
         private object? _selectedContent;
diff --git a/src/Avalonia.Controls/TextBox.cs b/src/Avalonia.Controls/TextBox.cs
index 50abfd23c8..64aace3a3b 100644
--- a/src/Avalonia.Controls/TextBox.cs
+++ b/src/Avalonia.Controls/TextBox.cs
@@ -24,7 +24,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// Represents a control that can be used to display or edit unformatted text.
     /// </summary>
-    [TemplatePart("PART_TextPresenter", typeof(TextPresenter))]
+    [TemplatePart("PART_TextPresenter", typeof(TextPresenter), IsRequired = true)]
     [TemplatePart("PART_ScrollViewer", typeof(ScrollViewer))]
     [PseudoClasses(":empty")]
     public class TextBox : TemplatedControl, UndoRedoHelper<TextBox.UndoRedoState>.IUndoRedoHost
diff --git a/src/Avalonia.Controls/ToggleSwitch.cs b/src/Avalonia.Controls/ToggleSwitch.cs
index 697dc4c2d0..1bea3b17a6 100644
--- a/src/Avalonia.Controls/ToggleSwitch.cs
+++ b/src/Avalonia.Controls/ToggleSwitch.cs
@@ -11,7 +11,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A Toggle Switch control.
     /// </summary>
-    [TemplatePart("PART_MovingKnobs",         typeof(Panel))]
+    [TemplatePart("PART_MovingKnobs",         typeof(Panel), IsRequired = true)]
     [TemplatePart("PART_OffContentPresenter", typeof(ContentPresenter))]
     [TemplatePart("PART_OnContentPresenter",  typeof(ContentPresenter))]
     [TemplatePart("PART_SwitchKnob",          typeof(Panel))]
diff --git a/src/Avalonia.Dialogs/ManagedFileChooser.cs b/src/Avalonia.Dialogs/ManagedFileChooser.cs
index 97730e8909..0bb5f28b89 100644
--- a/src/Avalonia.Dialogs/ManagedFileChooser.cs
+++ b/src/Avalonia.Dialogs/ManagedFileChooser.cs
@@ -11,8 +11,8 @@ using Avalonia.LogicalTree;
 
 namespace Avalonia.Dialogs
 {
-    [TemplatePart("PART_QuickLinks", typeof(Control))]
-    [TemplatePart("PART_Files",      typeof(ListBox))]
+    [TemplatePart("PART_QuickLinks", typeof(Control), IsRequired = true)]
+    [TemplatePart("PART_Files",      typeof(ListBox), IsRequired = true)]
     public class ManagedFileChooser : TemplatedControl
     {
         private Control? _quickLinksRoot;
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
index 0d70bc4db6..4cc5ffc779 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml
@@ -35,7 +35,7 @@
           <!-- To mimic WinUI SystemFocusVisual, Focus visual is drawn outside the bounds of the item -->
           <Border Name="Root" Background="{TemplateBinding Background}"
                   BorderThickness="0" ClipToBounds="True">
-            <ContentPresenter Name="Content"
+            <ContentPresenter Name="PART_ContentPresenter"
                               ContentTemplate="{TemplateBinding ContentTemplate}"
                               Content="{TemplateBinding Content}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
index 31280c6320..25b01cc5f8 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml
@@ -36,12 +36,12 @@
           <Border Name="Root" Background="{TemplateBinding Background}"
                   BorderThickness="0" ClipToBounds="True">
 
-            <ContentControl Name="Content"
-                            ContentTemplate="{TemplateBinding ContentTemplate}"
-                            Content="{TemplateBinding Content}"
-                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
-                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
-                            Margin="{TemplateBinding Padding}" />
+            <ContentPresenter Name="PART_ContentPresenter"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
+                              Content="{TemplateBinding Content}"
+                              HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
+                              VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
+                              Margin="{TemplateBinding Padding}" />
 
           </Border>
 
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
index ead55ac950..673a2b593c 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml
@@ -31,7 +31,7 @@
     <Setter Property="Template">
       <ControlTemplate>
         <!-- HCA was changed here to ensure nav arrows display correctly -->
-        <ContentPresenter Name="Text" Background="{TemplateBinding Background}"
+        <ContentPresenter Name="PART_ContentPresenter" Background="{TemplateBinding Background}"
                           BorderBrush="{DynamicResource CalendarViewNavigationButtonBorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml b/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
index 3bebc293d3..a2a61b1b02 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml
@@ -57,7 +57,7 @@
               </Panel>
             </Viewbox>
           </Grid>
-          <ContentPresenter x:Name="ContentPresenter"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                           ContentTemplate="{TemplateBinding ContentTemplate}"
                           Content="{TemplateBinding Content}"
                           Margin="{TemplateBinding Padding}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml b/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
index 9384eff8f4..23082f143e 100644
--- a/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml
@@ -55,7 +55,7 @@
                 that appear opaque. Not sure how MS does it though I suspect this is it
                 but source isn't MIT yet, so this is my solution -->
         <Border Background="{TemplateBinding Background}">
-          <ContentPresenter x:Name="ContentPresenter"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                   Background="{TemplateBinding Background}"
                   BorderBrush="{DynamicResource DateTimePickerFlyoutButtonBorderBrush}"
                   BorderThickness="{DynamicResource DateTimeFlyoutButtonBorderThickness}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml b/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
index e8c9ed9b2a..42ff4c4055 100644
--- a/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml
@@ -26,7 +26,8 @@
                 CornerRadius="{TemplateBinding CornerRadius}">
           <ScrollViewer HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}"
                         VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}">
-            <ContentPresenter Content="{TemplateBinding Content}"
+            <ContentPresenter x:Name="PART_ContentPresenter"
+                              Content="{TemplateBinding Content}"
                               ContentTemplate="{TemplateBinding ContentTemplate}"
                               Margin="{TemplateBinding Padding}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
diff --git a/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml b/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
index 9250b8e42d..6e9277df09 100644
--- a/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml
@@ -25,7 +25,7 @@
                     ClipToBounds="True">
               <DockPanel>
                 <Panel x:Name="PART_HeaderBar" Height="4" Background="{DynamicResource NotificationCardProgressBackgroundBrush}" DockPanel.Dock="Top" />
-                <ContentControl Name="PART_Content" MinHeight="64" Content="{TemplateBinding Content}" />
+                <ContentPresenter Name="PART_ContentPresenter" MinHeight="64" Content="{TemplateBinding Content}" />
               </DockPanel>
             </Border>
           </Border>
diff --git a/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml b/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
index 63352d6ee3..1107bf2c27 100644
--- a/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml
@@ -63,7 +63,8 @@
     <Setter Property="TextElement.Foreground" Value="{DynamicResource ScrollBarButtonArrowForeground}"/>
     <Setter Property="Template">
       <ControlTemplate>
-        <ContentPresenter Background="{DynamicResource ScrollBarButtonBackground}"
+        <ContentPresenter x:Name="PART_ContentPresenter"
+                          Background="{DynamicResource ScrollBarButtonBackground}"
                           BorderBrush="{DynamicResource ScrollBarButtonBorderBrush}"
                           Content="{TemplateBinding Content}"/>
       </ControlTemplate>
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
index 1e06368d24..17c2f6c612 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml
@@ -33,7 +33,7 @@
                      Opacity="0.5" />
 
           <!--  Focusable="False"  -->
-          <ContentPresenter Name="Content"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                             Margin="1,0,1,1"
                             HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                             VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
diff --git a/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml b/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
index e16b9f38ba..f499ef1258 100644
--- a/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/CalendarDayButton.xaml
@@ -36,15 +36,15 @@
                      IsVisible="False"
                      Opacity="0.5" />
 
-          <ContentControl Name="Content"
-                          Margin="5,1,5,1"
-                          HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
-                          VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
-                          Content="{TemplateBinding Content}"
-                          ContentTemplate="{TemplateBinding ContentTemplate}"
-                          FontSize="{TemplateBinding FontSize}"
-                          Foreground="{TemplateBinding Foreground}"
-                          Opacity="1" />
+          <ContentPresenter Name="PART_ContentPresenter"
+                            Margin="5,1,5,1"
+                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
+                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
+                            Content="{TemplateBinding Content}"
+                            ContentTemplate="{TemplateBinding ContentTemplate}"
+                            FontSize="{TemplateBinding FontSize}"
+                            Foreground="{TemplateBinding Foreground}"
+                            Opacity="1" />
 
           <Path Name="BlackoutVisual"
                 Margin="3"
diff --git a/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml b/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
index a606920e13..ab7ed0edb6 100644
--- a/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/DateTimePickerShared.xaml
@@ -64,7 +64,7 @@
           but source isn't MIT yet, so this is my solution
         -->
         <Border Background="{TemplateBinding Background}">
-          <ContentPresenter x:Name="ContentPresenter"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                             Padding="{TemplateBinding Padding}"
                             HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                             VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
diff --git a/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml b/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
index b6cf899fd5..538d66470a 100644
--- a/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/FlyoutPresenter.xaml
@@ -20,7 +20,8 @@
                 CornerRadius="{TemplateBinding CornerRadius}">
           <ScrollViewer HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}"
                         VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}">
-            <ContentPresenter Margin="{TemplateBinding Padding}"
+            <ContentPresenter x:Name="PART_ContentPresenter"
+                              Margin="{TemplateBinding Padding}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                               VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                               HorizontalContentAlignment="Stretch"
diff --git a/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml b/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
index 9cd095566a..fbb7c1d608 100644
--- a/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/NotificationCard.xaml
@@ -13,15 +13,14 @@
       <ControlTemplate>
         <LayoutTransformControl Name="PART_LayoutTransformControl"
                                 UseRenderTransform="True">
-          <Border Margin="8,8,0,0"
-                  Background="{TemplateBinding Background}"
-                  BorderBrush="{TemplateBinding BorderBrush}"
-                  BorderThickness="{TemplateBinding BorderThickness}"
-                  CornerRadius="{TemplateBinding CornerRadius}">
-            <ContentControl Name="PART_Content"
+          <ContentPresenter Name="PART_ContentPresenter"
                             MinHeight="150"
+                            Padding="8,8,0,0"
+                            Background="{TemplateBinding Background}"
+                            BorderBrush="{TemplateBinding BorderBrush}"
+                            BorderThickness="{TemplateBinding BorderThickness}"
+                            CornerRadius="{TemplateBinding CornerRadius}"
                             Content="{TemplateBinding Content}" />
-          </Border>
         </LayoutTransformControl>
       </ControlTemplate>
     </Setter>
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
index 480c74223f..bb3427e75a 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/AvaloniaXamlIlRuntimeCompiler.cs
@@ -215,14 +215,27 @@ namespace Avalonia.Markup.Xaml.XamlIl
                 HandleDiagnostic = (diagnostic) =>
                 {
                     var runtimeDiagnostic = new RuntimeXamlDiagnostic(diagnostic.Code.ToString(),
-                        (RuntimeXamlDiagnosticSeverity)diagnostic.Severity,
+                        diagnostic.Severity switch
+                        {
+                            XamlDiagnosticSeverity.None => RuntimeXamlDiagnosticSeverity.Info,
+                            XamlDiagnosticSeverity.Warning => RuntimeXamlDiagnosticSeverity.Warning,
+                            XamlDiagnosticSeverity.Error => RuntimeXamlDiagnosticSeverity.Error,
+                            XamlDiagnosticSeverity.Fatal => RuntimeXamlDiagnosticSeverity.Fatal,
+                            _ => throw new ArgumentOutOfRangeException()
+                        },
                         diagnostic.Title, diagnostic.LineNumber, diagnostic.LinePosition)
                     {
                         Document = diagnostic.Document
                     };
                     var newSeverity =
-                        (XamlDiagnosticSeverity?)configuration.DiagnosticHandler?.Invoke(runtimeDiagnostic) ??
-                        diagnostic.Severity;
+                        configuration.DiagnosticHandler?.Invoke(runtimeDiagnostic) switch
+                        {
+                            RuntimeXamlDiagnosticSeverity.Info => XamlDiagnosticSeverity.None,
+                            RuntimeXamlDiagnosticSeverity.Warning => XamlDiagnosticSeverity.Warning,
+                            RuntimeXamlDiagnosticSeverity.Error => XamlDiagnosticSeverity.Error,
+                            RuntimeXamlDiagnosticSeverity.Fatal => XamlDiagnosticSeverity.Fatal,
+                            _ => (XamlDiagnosticSeverity?)null
+                        } ?? diagnostic.Severity;
                     diagnostic = diagnostic with { Severity = newSeverity };
                     diagnostics.Add(diagnostic);
                     return newSeverity;
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
index ddc5e1c2de..2d3b7ce10a 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlDiagnosticCodes.cs
@@ -25,6 +25,9 @@ internal static class AvaloniaXamlDiagnosticCodes
     public const string PropertyPathError = "AVLN2202";
     public const string DuplicateSetterError = "AVLN2203";
     public const string StyleInMergedDictionaries = "AVLN2204";
+    public const string RequiredTemplatePartMissing = "AVLN2205";
+    public const string OptionalTemplatePartMissing = "AVLN2206";
+    public const string TemplatePartWrongType = "AVLN2207";
 
     // XAML emit errors 3000-3999.
     public const string EmitError = "AVLN3000";
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompiler.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompiler.cs
index 723675f975..ba23ad21ee 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompiler.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlCompiler.cs
@@ -76,6 +76,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             // After everything else
             InsertBefore<NewObjectTransformer>(
                 new AddNameScopeRegistration(),
+                new AvaloniaXamlIlControlTemplatePartsChecker(),
                 new AvaloniaXamlIlDataContextTypeTransformer(),
                 new AvaloniaXamlIlBindingPathTransformer(),
                 new AvaloniaXamlIlCompiledBindingsMetadataRemover()
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePartsChecker.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePartsChecker.cs
new file mode 100644
index 0000000000..2764971326
--- /dev/null
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePartsChecker.cs
@@ -0,0 +1,136 @@
+using System.Collections.Generic;
+using System.Linq;
+using XamlX;
+using XamlX.Ast;
+using XamlX.Transform;
+using XamlX.TypeSystem;
+
+namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers;
+
+internal class AvaloniaXamlIlControlTemplatePartsChecker : IXamlAstTransformer
+{
+    public IXamlAstNode Transform(AstTransformationContext context, IXamlAstNode node)
+    {
+        if (!(node is AvaloniaXamlIlTargetTypeMetadataNode on
+              && on.ScopeType == AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.ControlTemplate
+              // Styles with template selector will also return ScopeTypes.ControlTemplate, so we need to double check.
+              && on.Value.Type.GetClrType() == context.GetAvaloniaTypes().ControlTemplate))
+            return node;
+
+        var targetType = on.TargetType.GetClrType();
+        var templateParts = ResolveTemplateParts(targetType);
+
+        if (templateParts.Count == 0)
+            return node;
+
+        var visitor = new TemplatePartVisitor();
+        node.VisitChildren(visitor);
+
+        foreach (var pair in templateParts)
+        {
+            var name = pair.Key;
+            var (expectedType, isRequired) = pair.Value;
+
+            if (!visitor.TryGetValue(name, out var res))
+            {
+                if (isRequired)
+                {
+                    context.ReportDiagnostic(new XamlDiagnostic(
+                        AvaloniaXamlDiagnosticCodes.RequiredTemplatePartMissing,
+                        XamlDiagnosticSeverity.Error,
+                        $"Required template part with x:Name '{name}' must be defined on '{targetType.Name}' ControlTemplate.",
+                        node));
+                }
+                else
+                {
+                    context.ReportDiagnostic(new XamlDiagnostic(
+                        AvaloniaXamlDiagnosticCodes.OptionalTemplatePartMissing,
+                        XamlDiagnosticSeverity.None,
+                        $"Optional template part with x:Name '{name}' can be defined on '{targetType.Name}' ControlTemplate.",
+                        node));
+                }
+
+                continue;
+            }
+
+            if (expectedType is not null
+                && !expectedType.IsAssignableFrom(res.type))
+            {
+                context.ReportDiagnostic(new XamlDiagnostic(
+                    AvaloniaXamlDiagnosticCodes.TemplatePartWrongType,
+                    XamlDiagnosticSeverity.Error, 
+                    $"Template part '{name}' is expected to be assignable to '{expectedType.Name}', but actual type is {res.type.Name}.",
+                    res.line));
+            }
+        }
+
+        return node;
+    }
+
+    private static Dictionary<string, (IXamlType? type, bool isRequired)> ResolveTemplateParts(IXamlType targetType)
+    {
+        var dictionary = new Dictionary<string, (IXamlType? type, bool isRequired)>();
+        // Custom Attributes go in order from current type to base type. It should be possible to override parent template parts.
+        foreach (var attr in targetType.GetAllCustomAttributes())
+        {
+            if (attr.Type.Name == "TemplatePartAttribute")
+            {
+                if (!attr.Properties.TryGetValue("Name", out var nameObj))
+                {
+                    nameObj = attr.Parameters.FirstOrDefault();
+                }
+
+                if (!attr.Properties.TryGetValue("Type", out var typeObj))
+                {
+                    typeObj = attr.Parameters.Skip(1).FirstOrDefault();
+                }
+
+                attr.Properties.TryGetValue("IsRequired", out var isRequiredObj);
+
+                if (nameObj is string { Length :> 0 } name
+                    && !dictionary.ContainsKey(name))
+                {
+                    dictionary.Add(name, (typeObj as IXamlType, isRequiredObj as bool? == true));
+                }
+            }
+        }
+
+        return dictionary;
+    }
+
+    private class TemplatePartVisitor : Dictionary<string, (IXamlType type, IXamlLineInfo line)>, IXamlAstVisitor
+    {
+        private int _metadataScopeLevel = 0;
+        private Stack<IXamlAstNode> _parents = new();
+        
+        IXamlAstNode IXamlAstVisitor.Visit(IXamlAstNode node)
+        {
+            if (_metadataScopeLevel == 1
+                && node is AvaloniaNameScopeRegistrationXamlIlNode nameScopeRegistration
+                && nameScopeRegistration.Name is XamlAstTextNode textNode)
+            {
+                this[textNode.Text] = (nameScopeRegistration.TargetType, textNode);
+            }
+
+            return node;
+        }
+
+        void IXamlAstVisitor.Push(IXamlAstNode node)
+        {
+            _parents.Push(node);
+            if (node is NestedScopeMetadataNode)
+            {
+                _metadataScopeLevel++;
+            }
+        }
+
+        void IXamlAstVisitor.Pop()
+        {
+            var oldParent = _parents.Pop();
+            if (oldParent is NestedScopeMetadataNode)
+            {
+                _metadataScopeLevel--;
+            }
+        }
+    } 
+}
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePriorityTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePriorityTransformer.cs
index 76fd07f15c..05cdf32aec 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePriorityTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplatePriorityTransformer.cs
@@ -21,7 +21,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             // - The property has a single value
             if (node is XamlPropertyAssignmentNode prop &&
                 prop.Property is XamlIlAvaloniaProperty avaloniaProperty &&
-                context.ParentNodes().Any(IsControlTemplate) &&
+                context.ParentNodes().Any(c => c is AvaloniaXamlIlTargetTypeMetadataNode
+                {
+                    ScopeType: AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.ControlTemplate
+                }) &&
                 prop.Values.Count == 1)
             {
                 var priorityValueSetters = new List<IXamlPropertySetter>();
@@ -48,11 +51,5 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
             return node;
         }
-
-        private static bool IsControlTemplate(IXamlAstNode node)
-        {
-            return node is AvaloniaXamlIlTargetTypeMetadataNode tt &&
-                tt.ScopeType == AvaloniaXamlIlTargetTypeMetadataNode.ScopeTypes.ControlTemplate;
-        }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer.cs
index 4d93408ce8..afe4654df9 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlControlTemplateTargetTypeMetadataTransformer.cs
@@ -11,7 +11,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlAstNode Transform(AstTransformationContext context, IXamlAstNode node)
         {
             if (!(node is XamlAstObjectNode on
-                  && on.Type.GetClrType().FullName == "Avalonia.Markup.Xaml.Templates.ControlTemplate"))
+                  && on.Type.GetClrType() == context.GetAvaloniaTypes().ControlTemplate))
                 return node;
             var tt = on.Children.OfType<XamlAstXamlPropertyValueNode>().FirstOrDefault(ch =>
                                               ch.Property.GetClrProperty().Name == "TargetType");
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
index b5dfcc6861..9f46bccd90 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
@@ -120,6 +120,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType ControlTheme { get; }
         public IXamlType WindowTransparencyLevel { get; }
         public IXamlType IReadOnlyListOfT { get; }
+        public IXamlType ControlTemplate { get; }
 
         public AvaloniaXamlIlWellKnownTypes(TransformerConfiguration cfg)
         {
@@ -264,6 +265,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             UriConstructor = Uri.GetConstructor(new List<IXamlType>() { cfg.WellKnownTypes.String, UriKind });
             Style = cfg.TypeSystem.GetType("Avalonia.Styling.Style");
             ControlTheme = cfg.TypeSystem.GetType("Avalonia.Styling.ControlTheme");
+            ControlTemplate = cfg.TypeSystem.GetType("Avalonia.Markup.Xaml.Templates.ControlTemplate");
             IReadOnlyListOfT = cfg.TypeSystem.GetType("System.Collections.Generic.IReadOnlyList`1");
         }
     }
diff --git a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
index 068b116a45..8723ff4f90 100644
--- a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
@@ -39,13 +39,18 @@ public class RuntimeXamlLoaderConfiguration
 
 public enum RuntimeXamlDiagnosticSeverity
 {
-    None = 0,
-    
+    /// <summary>
+    /// Something that is an issue, as determined by some authority,
+    /// but is not surfaced through normal means.
+    /// There may be different mechanisms that act on these issues.
+    /// </summary>
+    Info = 1,
+
     /// <summary>
     /// Diagnostic is reported as a warning.
     /// </summary>
-    Warning = 1,
-    
+    Warning,
+
     /// <summary>
     /// Diagnostic is reported as an error.
     /// Compilation process is continued until the end of the parsing and transforming stage, throwing an aggregated exception of all errors.
diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
index e21f6cd276..b2c697cbad 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
@@ -1,6 +1,9 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
+using System.Xml;
 using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Data;
@@ -276,7 +279,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 <ControlTemplate xmlns='https://github.com/avaloniaui' 
                  xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
                  TargetType='{x:Type ContentControl}'>
-    <ContentPresenter Content='{TemplateBinding Content}' />
+    <ContentPresenter x:Name='PART_ContentPresenter' Content='{TemplateBinding Content}' />
 </ControlTemplate>
 ";
             var template = AvaloniaRuntimeXamlLoader.Parse<ControlTemplate>(xaml);
@@ -293,7 +296,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 <ControlTemplate xmlns='https://github.com/avaloniaui' 
                  xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
                  TargetType='ContentControl'>
-    <ContentPresenter Content='{TemplateBinding Content}' />
+    <ContentPresenter x:Name='PART_ContentPresenter' Content='{TemplateBinding Content}' />
 </ControlTemplate>
 ";
             var template = AvaloniaRuntimeXamlLoader.Parse<ControlTemplate>(xaml);
@@ -337,6 +340,103 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             var templateResult = template.Build(new TemplatedControl());
             Assert.Null(templateResult);
         }
+
+        [Fact]
+        public void ControlTemplate_Outputs_Error_When_Missing_TemplatePart()
+        {
+            using var _ = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var xaml = @"
+<ControlTemplate xmlns='https://github.com/avaloniaui'
+                 xmlns:controls='using:Avalonia.Markup.Xaml.UnitTests.Xaml'
+                 TargetType='controls:CustomButtonWithParts'>
+    <Border Name='PART_Typo_MainContentBorder'>
+        <ContentPresenter Name='PART_ContentPresenter'
+                          Content='{TemplateBinding Content}'/>
+    </Border>
+</ControlTemplate>";
+            var diagnostics = new List<RuntimeXamlDiagnostic>();
+            AvaloniaRuntimeXamlLoader.Load(new RuntimeXamlLoaderDocument(xaml), new RuntimeXamlLoaderConfiguration
+            {
+                LocalAssembly = typeof(XamlIlTests).Assembly,
+                DiagnosticHandler = diagnostic =>
+                {
+                    diagnostics.Add(diagnostic);
+                    return diagnostic.Severity;
+                }
+            });
+            var warning = Assert.Single(diagnostics);
+            Assert.Equal(RuntimeXamlDiagnosticSeverity.Info, warning.Severity);
+            Assert.Contains("'PART_MainContentBorder'", warning.Title);
+        }
+        
+        [Fact]
+        public void ControlTemplate_Outputs_Error_When_Using_Wrong_Type_With_TemplatePart()
+        {
+            using var _ = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var xaml = @"
+<ControlTemplate xmlns='https://github.com/avaloniaui'
+                 xmlns:controls='using:Avalonia.Markup.Xaml.UnitTests.Xaml'
+                 TargetType='controls:CustomControlWithParts'>
+    <Border Name='PART_MainContentBorder'>
+        <ContentControl Name='PART_ContentPresenter'
+                        Content='{TemplateBinding Content}'/>
+    </Border>
+</ControlTemplate>";
+            var diagnostics = new List<RuntimeXamlDiagnostic>();
+            Assert.ThrowsAny<XmlException>(() => AvaloniaRuntimeXamlLoader.Load(new RuntimeXamlLoaderDocument(xaml), new RuntimeXamlLoaderConfiguration
+            {
+                LocalAssembly = typeof(XamlIlTests).Assembly,
+                DiagnosticHandler = diagnostic =>
+                {
+                    diagnostics.Add(diagnostic);
+                    return diagnostic.Severity;
+                }
+            }));
+            var warning = Assert.Single(diagnostics);
+            Assert.Equal(RuntimeXamlDiagnosticSeverity.Error, warning.Severity);
+            Assert.Contains("'ContentPresenter'", warning.Title);
+        }
+
+        [Fact]
+        public void ControlTemplate_Outputs_Error_When_Missing_TemplatePart_Nested_ItemTemplate_Case()
+        {
+            using var _ = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var xaml = @"
+<ControlTemplate xmlns='https://github.com/avaloniaui'
+                 xmlns:controls='using:Avalonia.Markup.Xaml.UnitTests.Xaml'
+                 TargetType='controls:CustomControlWithParts'>
+    <Border Name='PART_Typo_MainContentBorder'>
+        <StackPanel>
+            <ItemsControl>
+                <ItemsControl.ItemTemplate>
+                    <DataTemplate>
+                        <!-- This PART_MainContentBorder shouldn't full parent ControlTemplate, PART_Typo_MainContentBorder still isn't properly named. -->
+                        <Border Name='PART_MainContentBorder' />
+                    </DataTemplate>
+                </ItemsControl.ItemTemplate>
+            </ItemsControl>
+            <ContentPresenter Name='PART_ContentPresenter'
+                              Content='{TemplateBinding Content}'/>
+        </StackPanel>
+    </Border>
+</ControlTemplate>";
+            var diagnostics = new List<RuntimeXamlDiagnostic>();
+            AvaloniaRuntimeXamlLoader.Load(new RuntimeXamlLoaderDocument(xaml), new RuntimeXamlLoaderConfiguration
+            {
+                LocalAssembly = typeof(XamlIlTests).Assembly,
+                DiagnosticHandler = diagnostic =>
+                {
+                    diagnostics.Add(diagnostic);
+                    return diagnostic.Severity;
+                }
+            });
+            var warning = Assert.Single(diagnostics);
+            Assert.Equal(RuntimeXamlDiagnosticSeverity.Info, warning.Severity);
+            Assert.Contains("'PART_MainContentBorder'", warning.Title);
+        }
     }
     public class ListBoxHierarchyLine : Panel
     {
@@ -349,4 +449,14 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             set => SetValue(LineDashStyleProperty, value);
         }
     }
+
+    [TemplatePart("PART_MainContentBorder", typeof(Border))]
+    [TemplatePart("PART_ContentPresenter", typeof(ContentPresenter))]
+    public class CustomControlWithParts : ContentControl
+    {
+    }
+
+    public class CustomButtonWithParts : CustomControlWithParts
+    {
+    }
 }