annotate with geoms "hline" and "vline" does not add a line

[aphalo]

I demonstrate the problem here only for geom_hline, but the same problem affects geom_vline.

ggplot(data.frame(x = 0:5, y = 0:5), aes(x, y)) +
     geom_point() +
     annotate(geom = "hline",
                     yintercept = 2.5)

Adding an y argument produces the expected output, with a warning:
Warning: Ignoring unknown aesthetics: y

ggplot(data.frame(x = 0:5, y = 0:5), aes(x, y)) +
    geom_point() +
    annotate(geom = "hline",
                    yintercept = 2.5, y = 2.5)

There is something odd going on: when y is present, the hline is plotted at the yintercept position, but the "ignored" unknown aesthetics still affects the scale limits.

ggplot(data.frame(x = 0:5, y = 0:5), aes(x, y)) +
     geom_point() +
     annotate(geom = "hline",
                     yintercept = 2.5, y = 100)

ggplot2 2.2.1.9000 installed minutes ago.

Hope this helps diagnose the problem.

[hadley]

Yes, unfortunately vline and hline are weird geoms that "self" annotate - just do geom_hline(yintercept = 2.5)