.NET for WebAssembly Debugger Support

Debugging is supported through the integration of a .NET Core CLI component, which acts as a static files server, as well as a debugger proxy for Chrome (other browsers are not supported).

Enable the Debugger support

In order to debug an Uno.Wasm.Boostrap enabled project, the Mono runtime debugger must be enabled:

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
   <MonoRuntimeDebuggerEnabled>true</MonoRuntimeDebuggerEnabled>
</PropertyGroup>

Debug symbols need to be emitted and be of the type portable:

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
    <DebugType>portable</DebugType>
    <DebugSymbols>true</DebugSymbols>
</PropertyGroup>

Finally, the DEBUG constant must be defined

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
    <DefineConstants>$(DefineConstants);TRACE;DEBUG</DefineConstants>
</PropertyGroup>

Doing so will enable the deployment of pdb files to the browser, and allow for the mono debugger proxy to use them.

For the time being, you will also need to make sure that mscorlib is disabled in the Linker configuration file:

<!-- Required for debugging -->
<assembly fullname="mscorlib" />
<assembly fullname="System.Core" />

.NET for WebAssembly now has integrated preliminary support for in-browser debugging. Refer to this document for up-to-date information on how to set up the debugging.

How to use the Browser debugger

The boostrapper also supports debugging directly in the browser debugging tools.

In Visual Studio:

• Make your project the startup project (right-click set as startup)
• In the debugging toolbar:
  • Select IIS Express as the debugging target
  • Select Chrome as the Web Browser
  • Make sure script debugging is disabled
• Start the debugging session using F5 (or Start Debug)
• Once your application has started, press Alt+Shift+D
• Follow the instructions on the web page
• You may need to refresh the original tab if you want to debug the entry point (Main) of your application.

Debugger troubleshooting

The debugger is still under development, and here are a few things to look for:

• Breakpoints set sometimes disappear when the debugged page is reloaded
• If none of your assemblies appear in the debugger window, it's generally caused by the debugger caching previously loaded files. Make sure to hit Ctrl+Shit+R to force reload the debugged page.

AOT Debugging and mono tracing (.NET 5 only)

When running with PG-AOT/FullAOT, exceptions generally do not provide stack traces, as WebAssembly as of the MVP does not yet support stack walking.

For the time being, it's still possible view browser stack traces in the log by enabling mono tracing.

First, you'll need to add the following class to your app:

static class MonoInternals
{
	[DllImport("__Native")]
	internal static extern void mono_trace_enable(int enable);
	[DllImport("__Native")]
	internal static extern int mono_trace_set_options(string options);
}

Note

In order for __Native to be available, you'll need to specify <WasmShellAdditionalPInvokeLibrary Include="__Native" /> item. See Static linking additional P/Invoke libraries for details.

Then in the Main of your application, add the following:

MonoInternals.mono_trace_enable(1);
MonoInternals.mono_trace_set_options("E:all");

This will enable the tracing of all application exceptions (caught or not), along with the associated native host stack traces.

You can find the documentation for mono_trace_set_options parameter here.