Allow to resuse value from previosu cell in data table

[jbytecoder]

I would like to suggest a new feature for data tables. data tables already allow to refer to variables to the left in the same row. I thought it would be great if it was also possible to reference value from same cell but from previous row. I managed to roll out my own solution for this by means of data pipes:

@Unroll("max(#a,#b)==#c")
  def 'Trick'( def a, def b, def c) {
    expect:
    Math.max(a, b) == c
    where:
    [a, b, c] << Spock.dataTable(
      [
        [5, 1, 5],
        [_, 2, _],
        [_, 3, _],
        [_, 4, _],
        [_, 5, _],
        [5, 6, 6]
      ]
    )
  }

and the dataTable function goes like this:

static List dataTable( List data ) {
        for( int i=0;i<data.size();++i ) {
            List row = data[i];
            for( int j=0;j<row.size();++j ) {
                if( row[j] instanceof Wildcard) {
                    row[j]=data[i-1][j]
                }
            }
        }
        data;
    }

It should be clear from the dataTable what is meant as the result.

I think that Spock AST transformation could easily perform the work for me Table of the form:

where:
 a | b | c
 5 | 1 | 5
 _ | 2 | _
 _ | 3 | _ 
 _ | 4 | _ 
 _ | 5 | _ 
 _ | 6 | 6

could easily be transformed to

where:
 a | b | c
 5 | 1 | 5
 5 | 2 | 5
 5 | 3 | 5 
 5 | 4 | 5 
 5 | 5 | 5 
 5 | 6 | 6

and the processed like any other dataTable

The reason for this feature would be that i'm working with long nested lists as values in table cells and i would like not to repeat my self