Contour labels are erased by axis flipping #2430
Description
When using the GR Backend, contour labels are correctly plotted until the axes are flipped. Other axis manipulation (e.g., changing the plot limits, either in the call or via xlims!) seem to leave the labels intact.
Here is an example, generated with Plots v0.28.4, GR v0.44.90, and Julia 1.2.0 (via JuliaPro)
Expected output is that the lower-left and upper-right plots have some contour labels, even if they're not always in exactly the same position. However, they are completely missing instead.
# Bivariate normal as an example
x = -7:0.05:7
y = x'
z = Matrix{Float64}(undef, length(x), length(y))
@. z = exp(-(x^2 + y^2/6))
levels = [0.0001, 0.01, 0.1]
import Plots
Plots.backend() # GR.backend
p1 = Plots.contour(x,y',z; levels=levels, contour_labels=true, title="No flip")
p2 = Plots.contour(x,y',z; levels=levels, contour_labels=true, title="xflip in call", xflip=true)
p3 = Plots.contour(x,y',z; levels=levels, contour_labels=true, title="Flipped afterward with xflip!")
Plots.xflip!(p3)
p4 = Plots.contour(x,y',z; levels=levels, contour_labels=true, ylims=(-5,5), title="Other axis manipulation")
Plots.xlims!(p4, -8,8)
Plots.plot(p1, p2, p3, p4)
Plots.savefig("/tmp/contour_bug_PlotsGR.png") #Uploaded aboveI have not tried this with other backends, since it doesn't run with PyPlot (See #2201 )