rlocusplot shows a very long warning with Plots

[ufechner7]

Example:

using ControlSystems, Plots
sys = tf([3, 1], [9, 7, 5, 6])
rlocusplot(sys, c=:blue)

(control) pkg> st
Status `~/repos/control/Project.toml`
  [a6e380b2] ControlSystems v1.5.2
  [91a5bcdd] Plots v1.37.2

Output:

julia> rlocusplot(sys, c=:blue) # colors are specified with the c or color keyword
┌ Warning: Keyword argument hover not supported with Plots.GRBackend().  Choose from: annotations, arrow, aspect_ratio, background_color, background_color_inside, background_color_outside, background_color_subplot, bar_width, bins, bottom_margin, camera, clims, color_palette, colorbar, colorbar_entry, colorbar_scale, colorbar_title, connections, contour_labels, discrete_values, fill_z, fillalpha, fillcolor, fillrange, fillstyle, flip, foreground_color, foreground_color_axis, foreground_color_border, foreground_color_grid, foreground_color_subplot, foreground_color_text, framestyle, grid, gridalpha, gridlinewidth, gridstyle, group, guide, guidefontcolor, guidefontfamily, guidefonthalign, guidefontrotation, guidefontsize, guidefontvalign, html_output_format, inset_subplots, label, layout, left_margin, legend_background_color, legend_font_color, legend_font_family, legend_font_halign, legend_font_pointsize, legend_font_rotation, legend_font_valign, legend_foreground_color, legend_position, legend_title, levels, lims, line_z, linealpha, linecolor, linestyle, linewidth, link, margin, marker_z, markeralpha, markercolor, markershape, markersize, markerstrokealpha, markerstrokecolor, markerstrokewidth, normalize, orientation, overwrite_figure, permute, polar, primary, projection, quiver, ribbon, right_margin, scale, series_annotations, seriesalpha, seriescolor, seriestype, show, show_empty_bins, size, smooth, subplot, subplot_index, tick_direction, tickfontcolor, tickfontfamily, tickfonthalign, tickfontrotation, tickfontsize, tickfontvalign, ticks, title, titlefontcolor, titlefontfamily, titlefonthalign, titlefontrotation, titlefontsize, titlefontvalign, top_margin, weights, widen, window_title, x, xdiscrete_values, xerror, xflip, xforeground_color_axis, xforeground_color_border, xforeground_color_grid, xforeground_color_text, xgrid, xgridalpha, xgridlinewidth, xgridstyle, xguide, xguidefontcolor, xguidefontfamily, xguidefonthalign, xguidefontrotation, xguidefontsize, xguidefontvalign, xlims, xlink, xscale, xtick_direction, xtickfontcolor, xtickfontfamily, xtickfonthalign, xtickfontrotation, xtickfontsize, xtickfontvalign, xticks, xwiden, y, ydiscrete_values, yerror, yflip, yforeground_color_axis, yforeground_color_border, yforeground_color_grid, yforeground_color_text, ygrid, ygridalpha, ygridlinewidth, ygridstyle, yguide, yguidefontcolor, yguidefontfamily, yguidefonthalign, yguidefontrotation, yguidefontsize, yguidefontvalign, ylims, ylink, yscale, ytick_direction, ytickfontcolor, ytickfontfamily, ytickfonthalign, ytickfontrotation, ytickfontsize, ytickfontvalign, yticks, ywiden, z, z_order, zdiscrete_values, zerror, zflip, zforeground_color_axis, zforeground_color_border, zforeground_color_grid, zforeground_color_text, zgrid, zgridalpha, zgridlinewidth, zgridstyle, zguide, zguidefontcolor, zguidefontfamily, zguidefonthalign, zguidefontrotation, zguidefontsize, zguidefontvalign, zlims, zlink, zscale, ztick_direction, ztickfontcolor, ztickfontfamily, ztickfonthalign, ztickfontrotation, ztickfontsize, ztickfontvalign, zticks, zwiden
└ @ Plots ~/.julia/packages/Plots/Hxe7H/src/args.jl:1553

[baggepinnen]

The warning is due to the plot recipe having hover information, but you’re plotting the GR, a backend that does not support hover information. If you use plotly, you can hover the mouse above the plot to see the gain value at a particular point on the curve.

This is really more of an issue with plots

[ufechner7]

Well, I guess it could be fixed in this package by using only keywords that are supported by the current backend.

[mzaffalon]

I would be against adding ad-hoc code only because it is not yet fixed in Plots. Moreover the warning appears only once.

[baggepinnen]

Adding code that tries to special-case Plots.jl backends have been fraught with bugs before, the backends keep changing and there are quite many of them. I'd thus also be reluctant to try to handle the differences between them. If you do not like the warning, you can silence it through other means for now, or use one of the backends that support the hover keyword, such as plotly().