geom_vline doesn't work with datetimes in x-axis

[lorin]

Here's an example that should show a vertical line through the third point, but doesn't:

import pandas as pd

from plotnine import *
from mizani.formatters import *

entries = [{"timestamp": pd.Timestamp("2017-11-30 12:16"), "count": 1},
           {"timestamp": pd.Timestamp("2017-11-30 12:17"), "count": 2}, 
           {"timestamp": pd.Timestamp("2017-11-30 12:18"), "count": 3}, 
           {"timestamp": pd.Timestamp("2017-11-30 12:19"), "count": 4}, 
           {"timestamp": pd.Timestamp("2017-11-30 12:20"), "count": 5}]
data = pd.DataFrame(entries)
ggplot(aes(x="timestamp", y="count"), data=data) + \ 
    geom_point() + \
    geom_vline(xintercept=data.timestamp[2]) + \
    scale_x_datetime(labels=date_format("%H:%M"))

Calling matplotlib.dates.date2num on the xintercept parameter works around this issue right now:

from matplotlib.dates import date2num

... + geom_vline(xintercept=date2num(data.timestamp[2])) + ...

[has2k1]

Other workarounds

# 1.
class my_scale_x_datetime(scale_x_datetime):
    aesthetics = ['x', 'xmin', 'xmax', 'xend', 'xintercept']

 ...
+ my_scale_x_datetime(labels=date_format("%H:%M"))

# 2.
 ...
 + scale_x_datetime(aesthetics= ['x', 'xintercept'], labels=date_format("%H:%M"))