Calculate the width of a geom_text in ggplot2

Question

When adding text labels next to (or above) bars with geom_text, there is no way to automatically leave enough room for the label. Example:

library(ggplot2)

pdata <- data.frame(group = c("A","B"), 
                    value = c(10,20), 
                    label = c("First label", "A long label"))

ggplot(pdata, aes(x = group, y = value)) +
  coord_flip() +
  geom_bar(stat = "identity") +
  geom_text(aes(label = label), hjust = -0.1)

I can of course manually change the axis limit so that the label fits, but I would like this to always work regardless of the input data.

My idea was to calculate the width of the labels in the current device (in relative 0-1 units of the figure region, or in user coordinates, both would work), but strwidth is not sufficient, and the grid package has some interesting functions which I cannot get to do what I want (convertWidth in particular).

How do I calculate the width of the label in the current plot so that I can adjust the axis limit automatically?

Thanks!