Getting the baked-in .pdb location from an assembly with Mono.Cecil 0.9.4

Because it isn't always as simple as

	public static string GetPdbFileName (string assemblyFileName)
	{
	return Path.ChangeExtension (assemblyFileName, ".pdb");
	}

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as is done in Mono.Cecil.Pdb.PdbHelper, if assemblies and symbols have been moved to separate locations during a build.

The tools are there -- we just need to get the debug data from the PE image if it's present, skip the first 24 bytes, and interpret the rest as a string. Alas, all the are annoyingly just slightly encapsulated from us. But never mind! Reflection gets us there without having to negotiate a patch or make a fork:

	/// <summary>
	/// Violate Cecil encapsulation to get the PDB path -- a candidate
	/// for another method on ModuleDefinition
	/// </summary>
	/// <param name="assembly">The assembly to find the .pdb path for</param>
	/// <returns>The path (null if the operation fails)</returns>
	public static string GetPdbFromImage(AssemblyDefinition assembly)
	{
	var m = assembly.MainModule;
	var imageField = typeof(ModuleDefinition).GetField("Image", BindingFlags.Instance | BindingFlags.NonPublic);
	var image = imageField.GetValue(m);
	var getDebugHeaderInfo = image.GetType().GetMethod("GetDebugHeader");
	byte[] result = null;
	var args = new object[] { result };
	try
	{
	getDebugHeaderInfo.Invoke(image, args);
	var SizeOfDebugInfo = 0x18;
	result = args[0] as byte[];
	if (null == result)
	{
	return null;
	}
	var byteValue = result.Skip(SizeOfDebugInfo).
	TakeWhile(x => x != 0).ToArray();
	if (byteValue.Length > 0)
	{
	// UTF-8 encoding works for an assembly named GetÞePdbLocation.
	return Encoding.UTF8.GetString(byteValue);
	}
	}
	catch (TargetInvocationException)
	{}
	return null;
	}

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