Sorting on macOS and Ubuntu acts differently

[duleorlovic]

I had a problem to run same code on different machines since the sort was giving different results for the array of rules with same properties.
Now we use sort_by.with_index so the order is preserved

[duleorlovic]

To see how sorting object with same property behaves differently on macOS and linux you can run:

# on linux the order preserved
8.times.map {|i| {i: i, p: 0}}.sort_by {|h| h[:p]}.map {|h| h[:i]}
 => [0, 1, 2, 3, 4, 5, 6, 7] 

# on mac the order is not original order
8.times.map {|i| {i: i, p: 0}}.sort_by {|h| h[:p]}.map {|h| h[:i]}
 => [7, 1, 2, 3, 4, 5, 6, 0] 

# on mac for small arrays works stable
7.times.map {|i| {i: i, p: 0}}.sort_by {|h| h[:p]}.map {|h| h[:i]}
 => [0, 1, 2, 3, 4, 5, 6] 

That is the reason why I update lib/core/engine.rb to

agenda.sort_by.with_index { |a, i| [a, i] }

so we have original order preserved

8.times.map {|i| {i: i, p: 0}}.sort_by.with_index {|h, n| [h[:p], n]}.map {|h| h[:i]}
 => [0, 1, 2, 3, 4, 5, 6, 7] 

and engines rules are performed in the same order on both mac and linux