Are dates actually needed to trigger this?

I cannot be absolutely sure but I haven't been able to recreate it with plain text labels. For example

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import datetime

datax = [1,2,3]
labels = ['Zero', 'One', 'Two', 'Three', 'Four', 'Five', 'Six', 'Seven','Eight', 'Nine']
data1 = [5,8,12]

fig, ax = plt.subplots(1, 1, figsize=(20/2.54, 12/2.54))
plt.subplots_adjust(left=0.08, bottom=0.15, right=0.95)
plt.title("x-axis label angle bug")
b1 = ax.bar(datax, data1, width=0.7)

ax.set_xticklabels(labels, rotation=30, ha='right')

plt.axvline(x=7)
plt.show()

Works as expected.

I actually realized there is a trivial workaround and that is to change the order of the adjustment of the labels and additional graph details. So instead of

plt.xticks(rotation=30, ha="right")
plt.axvline(x=datetime.datetime(2022, 3, 15, 0, 0))

you swap to

plt.axvline(x=datetime.datetime(2022, 3, 15, 0, 0))
plt.xticks(rotation=30, ha="right")

it works since I assume that with the addition of the vline the xmax is adjusted and the full scale range is subjected to the rotation adjustment. So this seems highly likely (but not certain) to be some corner case involving date axis generation.

@jklymak I can work on this if this is still an issue. Just want to make sure i understand the problem correctly, if the xticks method is used before the axvline method, the date should still rotate as shown in the expected outcome. Is this correct?

@mylasem Correct, independently of what plotting is done and in what order, all of the ticks should be rotated the same.

is probably the cause. We may have more ticks allocated internally than are returned by get_xticklabels.

That said, we haven't specified the behavior of plt.ticks(**kwargs). Does it only apply to current tick labels (which I think is the cause of the present issue), or does it define a global state similar to plt.tick_params(). If the latter, we probably have to tap into the mechanics used in tick_params(). Note however that parameter names may differ and we'd have to make sure to accept exactly the Text properties.
This might be a bit tedious. Therefore, I could also see an argument for not allowing plt.ticks(**kwargs), and instead refer the user to tick_params().

Any workarounds ?

Call fig.draw_without_rendering before rotating the ticks?

Call fig.draw_without_rendering before rotating the ticks?

I have the same problem, with the second tick (also a date) being the only one which is not rotated. I am using :
plt.setp(ax.get_xticklabels(), rotation=30, ha='right')

And this workaround works for me, thanks!

The recommended solution from 3.11 on will be the new tick rotations modes introduced in #28968, i.e. here

plt.xaxis.set_tick_params(rotation=30, rotation_mode="xtick")

I'm closing this as there is a current workaround (fig.draw_without_rendering()) and a better future tick styling using tick_params.