Can .NET source code hard-code a debugging breakpoint?

You probably are after something like this:

if(System.Diagnostics.Debugger.IsAttached)
  System.Diagnostics.Debugger.Break();

Of course that will still get compiled in a Release build. If you want it to behave more like the Debug object where the code simply doesn't exist in a Release build, then you could do something like this:

    // Conditional("Debug") means that calls to DebugBreak will only be
    // compiled when Debug is defined. DebugBreak will still be compiled
    // even in release mode, but the #if eliminates the code within it.
    // DebuggerHidden is so that, when the break happens, the call stack
    // is at the caller rather than inside of DebugBreak.
    [DebuggerHidden]
    [Conditional("DEBUG")] 
    void DebugBreak()
    {
        if(System.Diagnostics.Debugger.IsAttached)
            System.Diagnostics.Debugger.Break();
    }

Then add a call to it in your code.

System.Diagnostics.Debugger.Break?

I ran into a situation once where this didn't work

System.Diagnostics.Debugger.Break();

but this did

System.Diagnostics.Debugger.Launch();

If you want to have only one line of code instead of 4, wrap

#if DEBUG
       if (Debugger.IsAttached)
            Debugger.Break();
#endif

into

public static class DebugHelper
{
    [DebuggerHidden]
    [Conditional("DEBUG")]
    public static void Stop()
    {
       if (Debugger.IsAttached)
            Debugger.Break();
    }
}

and use

DebugHelper.Stop();

DebuggerHiddenAttribute has been added to prevent the debugger from stopping on the inner code of the Stop method and from stepping into the method with F11.