step, step, step

[Rocky Bernstein]

I've just finished a bout of hacking in order to try to get stepping granularity on the rubinius trepanning debugger feel right. Again. 

Lest one think this is just something I have trouble with, I've encountered and reported 3 issues in the rubinius reference debugger #565, #578 and #593. 

Why is stepping in ruby debuggers a problem? 

On the one hand It is not uncommon for someone to complain that they were stepping along and the debugger stepped right over where they wanted to stop. And then there is other end of the spectrum: in Ruby one can write in a streaming or functional style and that is a good thing. So here one get complaints that stepping is just too tedious. Even with the traditional 3 variations of step: "step into" (step), "step over" (next) and "step out" (finish). 

I think it was in order to address this tedium that Kent Siblev added a "mode" called "set force" which forces stepping to stop at a new line number. In the trepanning debuggers, "set force" is now called "set different". And I've added suffixes to the step commands to set the mode for that one step. So "s+" sets the "different" on for the one command no matter what the mode was. Likewise "s-" sets "different off" for the one command. 

This helps but, in my own use I don't think this goes far enough. And to go one level further is where Ruby 1.9.2 and rubinius diverge. 

In Ruby 1.9.2, many system-implemented calls are C functions (like "upto" or "times"). So the way we can filter out those calls and returns is by saying we want to skip C call/return events. (Right now you can't step within the assembly language instructions of a C function.)  However in Rubinius "upto" and "times" are written in Ruby.  

So what I just finished hacking into the Rubinius trepanning debugger was adding a mechanism to filter methods by their source location. In Rubinius many of the built-in methods have a file locations that starts "kernel/". Note that this filename is a relative path and is stored that way even though other file names are generally stored as absolute file names. If it turns out there are other locations, I can easily more locations in. 

And as with C events in 1.9.2 one can switch the defaults. 

Finally I should note that stepping doesn't change the way breakpoints work. You can always set a breakpoint on a 1.9.2 C function or a Rubinius kernel method; hitting a breakpoint is independent of any kind of stepping that is performed.