is there a tool to propagate preprocessor directives?

Question

Suppose I have the following class definition:

class foo
{
    #if bar
    private bool bar;
    #endif
    public void Do()
    {
        bar = false;
    }
}

Is there a way to propagate the preprocessor directive wrapping bar to every place where bar is used. The output should be something like this:

class foo
{
    #if bar
    private bool bar;
    #endif
    public void Do()
    {
        #if bar
        bar = false;
        #endif
    }
}

Answer 1

No, basically. However, what you can do is split your code into two files and make use of partial class such that all your bar code is in one isolated file:

partial class foo
{
    partial void OnBar(bool value);
    public void Do()
    {
        OnBar(false);
    }
}

and

#if bar
partial class foo
{
    private bool bar;
    partial void OnBar(bool value)
    {
        bar = value;
    }
}
#endif

Now the main file knows nothing about bar. If the bar compilation symbol isn't defined, the bar field doesn't exist, and nor does the OnBar method - the method and it's invocations simply evaporate.

This can be useful in many scenarios, including additional levels of debugging code, or targeting multiple platforms / frameworks / operating systems (with specific files for different targets) - without your code being filled with #if.