Add Source Navigation Support Across XAML, Previewer, and DevTools

[Unrealiter]

What does the pull request do?

This pull request implements AXAML Source Information support for debug builds and adds a corresponding “Jump to Source” experience in Avalonia’s design-time and diagnostic tooling.

Concretely, it:

• Extends the AXAML compiler to embed source metadata (file path, line, and column) into the generated output for debug builds.
• Adds a “Jump to Source” button in the DevTools tree, and a “Jump to Source” overlay in the Designer.

Related feature request: Add AXAML Source Information and “Jump to Source” support for Debug Builds #19962.

What is the current behavior?

Currently, when working with Avalonia in design-time or diagnostics tooling:

• There is no fast path to navigate from a visual element back to the original .axaml definition.
• Designer and DevTools can show the visual tree, but lack reliable source mapping (file + line/column) for elements.
• Debugging complex layouts, inspecting control hierarchies, or exploring large XAML codebases is cumbersome because developers must manually search for the corresponding XAML.

What is the updated/expected behavior with this PR?

With this PR:

• Debug builds of AXAML views include source metadata (file path, line, and column) for each generated element.
  This is added through an attached property: Avalonia.Markup.Xaml.SourceInfo.Source.SourceInfo.
  In addition, the XAML compiler will add a XamlSourceInfoAttribute to each XAML-backed class, mapping it to the path of the corresponding XAML file.
  Source info generation can be controlled via the AvaloniaXamlCreateSourceInfo project setting, which allows you to explicitly enable or disable SourceInfo creation. If this setting is not specified, it defaults to true for Debug builds and false for non-Debug builds.

• The Designer allows users to:

  • Select an element on the design surface.
  • Invoke “Jump to Source” to open the corresponding .axaml file at the correct line/column in the configured editor/IDE.
  • Use MouseWheel or Shift+MouseClick (up) / Ctrl+MouseClick (down) to control which element to jump to in the visual tree.
  • Disable the mouse selection highlight with a small option button.

• The Avalonia.Diagnostics DevTools:

  • Exposes a “Jump to Source” button next to the name of each entry in the tree (similar to the WPF debug tree).
  • Navigates to the source definition for the selected visual element when triggered.
  • Handles the case where navigation is not available (for example, if no source information is present).

• Supported backends: Visual Studio, Rider, Visual Studio Code

  • Adds a IAvaloniaSourceNavigator interface and a registry so anyone can plug in their own navigator:

public interface IAvaloniaSourceNavigator
{
    // Determines whether this navigator is able to handle navigation.
    bool CanNavigate();

    // Attempts to navigate to the specified file and position.
    Task NavigateToAsync(string filePath, int line, int column);
}

public class SourceNavigatorRegistry
{
    public static void Register(IAvaloniaSourceNavigator navigator) { ... }
}

For example, to open the XAML file in Windows Notepad, one may register the following NotepadNavigator:

class NotepadNavigator : Avalonia.Markup.Xaml.SourceInfo.IAvaloniaSourceNavigator
{
    public bool CanNavigate() => true;

    public async Task NavigateToAsync(string filePath, int line, int column)
    {
        Process.Start("C:\\Windows\\notepad.exe", filePath);
    }
}

Example in Designer:

2025-11-01.00-03-01.mp4

Example in DevTools:

2025-11-01.00-11-21.mp4

Example in Rider + MouseWheel selection at the end:

2025-11-17.17-22-43.mp4

Breaking changes

None.

Obsoletions / Deprecations

None.

Fixed issues

Fixes #19962

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0060100-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

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[grokys]

Hi @Unrealiter - thanks for opening this PR - this is something that I have a POC for myself but I've not had time yet to open a PR.

This PR seems to add 4 separate things:

1. XamlX changes to include SourceInfo
2. IAvaloniaSourceNavigator infra in the Avalonia.Markup.Xaml
3. Old VS extension previewer overlay allowing to click on elements and navigate in the source
4. Old DevTools button to navigate to the element in the tree

Personally, I'd definitely be interested in item 1 but we'd probably want to discuss whether this repository is the correct place for 2 and 3. I think we'd be able to get 1 merged more speedily if it were separated into a separate PR. Does that sound like a good idea to you?

With regards to 1, I'll leave some comments with my thoughts in the PR for now.

[grokys]

Just commenting on the XAML source info part for now.

[grokys]

Rather than the position of the element in the source file, ideally we'd be storing the span of the element in the source file. This would allow us to match elements to source in the opposite direction - that is, when the user moves the caret in the XAML file, we can highlight the relevant control in the preview.

[Unrealiter]

Is the span strictly necessary in this case?

I’d assume that the IDE/plugin issuing a “source → element selection” query already has a parsed XML tree available (it needs that anyway for things like code completion). Given an arbitrary caret position in the file, it should be able to resolve the corresponding (or nearest) XML node start.

If the Avalonia designer exposed an API like “get all AvaloniaObjects associated with XML node starting at position X”, that should be enough to support the reverse mapping as well, without having to store explicit spans for each element.

[grokys]

It's not a good idea to name a class the same as its containing namepace

[grokys]

This is more me thinking aloud than anything else, but I'm not sure it's a good idea for this to be a struct? It limits what we can do with this type, and it's going to be boxed anyway if stored in an attached property.

[grokys]

Source is quite a generic name. I'd probably prefer something more descriptive, such as MAUI's VisualDiagnostics or we might even want to consider adding it directly to the existing Design class?

[grokys]

My POC also used an attached property, but I know that MAUI uses a ConditionalWeakTable so that non-BindableObject /AvaloniaObjects can also have their source tracked (I assume). I'm not sure what the use-case for this is however.

@drasticactions @jsuarezruiz I'd be interested in your thoughts here.

[Unrealiter]

My main use case was mapping visual elements in the designer to the appropriate XAML location, which is why I chose AvaloniaObject. I think even most of the “non-visual” elements that one might consider for source mapping, like ControlThemes or Styles, inherit from AvaloniaObject.

[Unrealiter]

By keeping the mapping in a separate store instead of an attached property, I could imagine also supporting the reverse operation (e.g., given a span in XAML, find the corresponding AvaloniaObject instances that represent that piece of source code).

[grokys]

I assume this is needed because:

// Add [XamlSourceInfoAttribute] to the generated class.
// Used at design time to locate the original .axaml file,
// since the runtime loader substitutes a fake file name.

This feels like a bit of a hack. Is it not possible to make the runtime loader use the correct filename?

[Unrealiter]

I don’t know why there is no filename.
The protocol for the designer even has a XamlFileProjectPath:

public class UpdateXamlMessage
{
     public string Xaml { get; set; }
     public string AssemblyPath { get; set; }
     public string XamlFileProjectPath { get; set; }
 }

But for me it was null in both Visual Studio and Rider.

In addition, DesignerWindowLoader.LoadDesignerWindow has:

if (xamlFileProjectPath == null)
    xamlFileProjectPath = "/Fake.xaml";
// Fabricate fake Uri
baseUri =
   new Uri($"avares://{Path.GetFileNameWithoutExtension(assemblyPath)}{xamlFileProjectPath}");

[maxkatz6]

There is a problem with responsibility which process should "jump to source", from how designer changes are implemented in this PR.
In this PR, previewed app process pings IDE process directly. It is an easier approach and would work well with, for example, devtools.

But this approach will conflict with kinds of deeper integration between previewer and IDE.
For example, we had experimented before with previewer, to select specific control span from start position to end position with new VS extension. That's what also Steven mentioned.

For the old previewer, I think, it would make the most sense to extend Previewer protocol API by adding new message ("JumpToSourceRequested"?) and handle this message on the IDE side. You can find existing previewer API here.

[maxkatz6]

With old DevTools in this repository, we do not add any new features anymore, but once XAML compiler/source related changes are merged in this PR, I can update new DevTools accordingly. Such feature will be part of free community edition.

[Unrealiter]

I agree that, for the designer, adding a JumpToSource action is probably the cleanest solution, though it requires changes in the VS Code, Rider, and Visual Studio (closed source) plugin implementations.

This would also probably lead to different implementations in the dev tools (for example, a CLI command in DevTools and an IDE-specific plugin command in the designer), since DevTools is not connected through the designer API, correct?
On the other hand, the IDE-specific plugin command would potentially result in a more robust and performant solution.