Re: [BUG-ish] diff compaction heuristic false positive

> On Fri, Jun 10, 2016 at 10:31:13AM +0200, Michael Haggerty wrote:
> 
>> I've often thought that indentation would be a good, fairly universal
>> signal for diff to use when deciding how to slide hunks around. Most
>> source code is indented in a way that shows its structure.
>>
>> I propose the following heuristic:
>>
>> * Prefer to start and end hunks following lines with the least
>>   indentation.
>>
>> * Define the "indentation" of a blank line to be the indentation of
>>   the previous non-blank line minus epsilon.
>>
>> * In the case of a tie, prefer to slide the hunk down as far as
>>   possible.
> 
> Hmm. That might help this case, but the original motivation for this
> heuristic was something like:
> 
>   ##
>   # foo
>   def foo
>     something
>   end
> 
>   ##
>   # bar
>   def bar
>     something_else
>   end
> 
> where we add the first function above the second. We end up with:
> 
> diff --git a/file.rb b/file.rb
> index 1f9b151..f991c76 100644
> --- a/file.rb
> +++ b/file.rb
> @@ -1,4 +1,10 @@
>  ##
> +# foo
> +def foo
> +  something
> +end
> +
> +##
>  # bar
>  def bar
>    something else
> 
> I.e., crediting the "##" to the wrong spot (or in C, the "/*"). I don't
> think indentation helps us there (sliding-up would, but like
> sliding-down, it just depends on the order of the hunks).
> 
> So I agree that adding indentation to the mix might help, but I don't
> think it can replace this heuristic.