scale_[xy]_discrete() causes removal of breaks/labels

[gfiumara]

Summary

Using scale_[xy]_discrete(), regardless of arguments, causes axis labels and breaks to disappear without warning.

Example

library(ggplot2)
xyDF <- data.frame(x = 1:10, y = 1:10)
ggplot(data = xyDF, mapping = aes(x = x, y = y)) +
    geom_line() +
    geom_point() +
    scale_x_discrete()

Expected results

Plot showing breaks and labels at 1:10 on the X axis.

Created with ggplot2 1.0.1, as I cannot reproduce with 2.1.0.

Actual results

Plot with no breaks or labels on the X axis (as if scale_x_discrete(labels = NULL, breaks = NULL) was added to the plot instead of the default waiver()).

Notes

• Regression since ggplot2 1.0.1 (last major version I've been using) fb3931c.
• Present in devtools and CRAN version as of 22 March 2016.

[gfiumara]

Appears to have broken in commit 89893c7 (#1542), confirmed by running sample with different devtools installs:

# Works
devtools::install_github("hadley/ggplot2", ref="fb3931c4e925272ddba607b81ada998df630bc10")

# Broken in subsequent commit
devtools::install_github("hadley/ggplot2", ref="89893c71ea575e198240e008ba2f42c9cbb7c6b7")

[thomasp85]

This is an by design, as conversion from continuous to discrete data is not well-defined. It is easy to end up with thousands of breaks so it is up to the user to either provide the breaks explicitly or convert their data to a discrete format