callr 3.7.2

New function add_hook() to hook into the callr process startup and options. This is for experts and it is also currently experimental (#203, @klmr).

callr 3.7.1

When copying existing startup files, an additional newline is appended to protect against a missing newline at the end of the file. This would cause R ignore that line (#205).
Serialization of objects passed between sessions now uses compress=FALSE by default. The default can be changed by setting the callr.compress_transport option (#223, @dfalbel).
We have revamped callr’s error objects, with lots of improvements to the output.

Reporting errors is much faster now (#185).
The user_profile option of r_vanilla() defaults to FALSE now (#194).
It is now possible to set R environment variables (R_ENVIRON_USER, R_PROFILE_USER, etc.) via the env argument (#193).

callr now supports starting an R process with a different architecture, so on Windows 64-bit R can start a 32-bit R background process, and vice-versa (#95).
callr now handles symbolic arguments properly, and does not evaluate them. E.g. callr::r(function(x) x, list(quote(foobar))) works now (#175).
callr::r_session does not leak file descriptors now in the sub-process (#184).

callr can now pass the environment of the function to the subprocess, optionally. This makes it easier to call an internal function of a package in a subprocess. See the package argument of r(), r_bg(), r_session$run(), etc. (#147).

An r_session now exits if the load hook errors. This generates an error if the session is started with wait = TRUE. For wait = FALSE the first $read() operation will return with an error (#162).

default_repos() now returns a list if getOption("repos") is a list, and a vector otherwise, on R 4.x.y as well.

Improved error messages. Error messages are now fully printed after an error. In non-interactive sessions, the stack trace is printed as well.

callr is now more careful when loading the local .Rprofile in the subprocess. This fixes issues with packrat and renv that use .Rprofile for setup (#139).
callr functions fail early if environment file is missing (#123, @jdblischak)

All callr functions and background processes properly clean up temporary files now (#104).
callr now uses a more principled setup for the library path, and restores the related environment variables in the child process. This is a breaking change if you relied on having the library set in a system() subprocess of the callr subprocess (#114).
Better printing of rlang_errors that happened in the subprocess.
The stacking of error objects is slightly different now, as we keep the unmodified error from the subprocess in $parent$error.
callr now loads .Rprofile files from the current working directory by default. This works better with packrat, renv, and other software that relies on a local profile for initialization (#131).

No user visible changes in this version.

r_session now avoids creating data and env objects in the global environment of the subprocess.
New $debug() method for r_session to inspect the dumped frames in the subprocess, after an error.

callr now sets the .Last.error variable for every uncaught callr error to the error condition, and also sets .Last.error.trace to its stack trace. If the error originates in the subprocess, then .Last.error is a hierarchical error object, and .Last.error.trace merges the traces from the two processes. See the README.md for an example.
New $traceback() method for r_session, to run traceback() in the subprocess, after an error.
A callr subprocess now does not load any R packages by default.
New vignette, that showcases r_session.

r(), rcmd() and rscript() can now redirect the standard error of the subprocess its standard output. This allows to keep them correctly interleaved. For this, you need to either set the stderr argument to the special string "2>&1", or to the same output file as specified for stdout.
r(), rcmd() and rscript() now pass ... arguments to processx::run(). r_bg() and rcmd_bg() pass ... arguments to the processx::process constructor. For r_process, rcmd_process and rscript_process extra arguments can be specified as options$extra, these are also passed to the processx::process constructor (#100).

r(), r_bg(), etc. now handle messages from the cliapp package properly. They used to make the R session exit.
Better default for the repos option in callr subprocesses. callr no longer creates duplicate “CRAN” entries. By default the new default_repos() function is used to set repos in the subprocess.

New rscript() function and rscript_process class to execute R scripts via Rscript (#40, #81).
Library paths are now correctly set up for system() (and similar) calls from the callr subprocesses (#83, #84).
Pass options("repos") to the child process as is, without checking. Closes #82.
r_session$run_with_output() now returns an S3 object with class callr_session_result.
r_session$run*() handle interrupts properly. It tries to interrupt the background process fist, kills it if it is not interruptible, and then re-throws the interrupt condition, going back to the top level prompt if the re-thrown condition is uncaught.

pkgdown web site at https://callr.r-lib.org (#52, #53).
callr users .Renviron files now (and R_ENVIRON_USER as well), but overrides the library path, as requested in r(), etc. (#30).
callr now handles the case when the subprocess calls quit().
callr now uses the processx package, instead of embedded code, to create and control processes.

Fix a bug with R-devel, caused by the change on 2018-02-08: https://github.com/wch/r-source/commit/924582943706100e88a11d6bb0585d25779c91f5 #37, #38
Fix a race condition on Windows, when creating named pipes for stdout or stderr. The client sometimes didn’t wait for the server, and callr failed with ERROR_PIPE_BUSY (231, All pipe instances are busy).

Run R or R CMD in the background, see r_bg(), rcmd_bg(), and also r_process and rcmd_process
The defaults for r() are safer now, the match the defaults of r_safe(). r_safe() is kept for compatibility. r_copycat() has the old r() defaults.
The defaults for rcmd() are safer now, the match the defaults of rcmd_safe(). rcmd_safe() is kept for compatibility. rcmd_copycat() has the old rcmd() defaults.
Support block callbacks, in addition to line callbacks. Block callbacks are called for arbitrary chunks of output, even without a newline
Add spinner argument to show a spinner in r() or rcmd()
Support timeouts, via the timeout argument
Fix bug when stdout and stderr are redirected to the same file
rcmd_safe_env() to allow extending the environment variables set in safe mode
rcmd() gets a fail_on_status argument
rcmd() gets an echo argument to potentially show the command to be run on the screen (#15)
rcmd() gets a wd argument to set the working directory

First public release.