scale.zero option not useful for plotting negative numbers

[skybrian]

If I turn on the "zero" option for data that consists entirely of negative numbers, Plot doesn't choose a useful domain. In this case, the data contains values from -2 to -0.5, so a good domain including zero would be [-2, 0]. It seems to be picking something like [0, -0.5] instead, which is backwards and means that most points aren't plotted.

Plot.plot({
  width: width,
  height: 200,
  y: {zero: true},
  marks: [
    Plot.lineY([-1, -2, -0.5])],
});

Demo here.

A workaround is to set the domain manually.

[mbostock]

Draft fix in #934.