store the error message and show it in Rscript_call(); this will be m…

…uch more informational than the original error message

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: xfun
 Type: Package
 Title: Supporting Functions for Packages Maintained by 'Yihui Xie'
-Version: 0.44.2
+Version: 0.44.3
 Authors@R: c(
   person("Yihui", "Xie", role = c("aut", "cre", "cph"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
   person("Wush", "Wu", role = "ctb"),

NEWS.md

@@ -2,6 +2,8 @@
 
 - For `record()` with `verbose = 1` or `2`, invisible `NULL` is no longer printed.
 
+- `Rscript_call()` will show the actual error message (if an error occurred) during calling the function in a new R session.
+
 # CHANGES IN xfun VERSION 0.44
 
 - Added a function `cache_exec()` to cache the execution of an expression either in memory or on disk. It is much more general and flexible than `cache_rds()`. For example, it supports custom reading/writing methods for cache files, and can load locally created variables in the expression while loading cache.

R/command.R

@@ -63,18 +63,23 @@ Rcmd = function(args, ...) {
 #' Call a function in a new R session via `Rscript()`
 #'
 #' Save the argument values of a function in a temporary RDS file, open a new R
-#' session via [Rscript()], read the argument values, call the
-#' function, and read the returned value back to the current R session.
+#' session via [Rscript()], read the argument values, call the function, and
+#' read the returned value back to the current R session.
 #' @param fun A function, or a character string that can be parsed and evaluated
 #'   to a function.
 #' @param args A list of argument values.
-#' @param options A character vector of options to passed to
-#'   [Rscript()], e.g., `"--vanilla"`.
+#' @param options A character vector of options to passed to [Rscript()], e.g.,
+#'   `"--vanilla"`.
 #' @param ...,wait Arguments to be passed to [system2()].
 #' @param fail The desired error message when an error occurred in calling the
-#'   function.
+#'   function. If the actual error message during running the function is
+#'   available, it will be appended to this message.
 #' @export
-#' @return The returned value of the function in the new R session.
+#' @return If `wait = TRUE`, the returned value of the function in the new R
+#'   session. If `wait = FALSE`, three file paths will be returned: the first
+#'   one stores `fun` and `args` (as a list), the second one is supposed to
+#'   store the returned value of the function, and the third one stores the
+#'   possible error message.
 #' @examples factorial(10)
 #' # should return the same value
 #' xfun::Rscript_call('factorial', list(10))
@@ -86,16 +91,19 @@ Rcmd = function(args, ...) {
 #' xfun::Rscript_call(factorial, list(10), options = c("--vanilla"))
 Rscript_call = function(
   fun, args = list(), options = NULL, ..., wait = TRUE,
-  fail = sprintf("Failed to run '%s' in a new R session.", deparse(substitute(fun))[1])
+  fail = sprintf("Failed to run '%s' in a new R session", deparse(substitute(fun))[1])
 ) {
-  f = replicate(2, tempfile(fileext = '.rds'))
-  on.exit(unlink(if (wait) f else f[2]), add = TRUE)
+  f = replicate(3, tempfile(fileext = '.rds'))
+  on.exit(if (wait) unlink(f), add = TRUE)
   saveRDS(list(fun, args), f[1])
-  Rscript(
-    c(options, shQuote(c(pkg_file('scripts', 'call-fun.R'), f)))
-    ,..., wait = wait
+  res = Rscript(
+    c(options, shQuote(c(pkg_file('scripts', 'call-fun.R'), f))), ..., wait = wait
   )
-  if (wait) if (file_exists(f[2])) readRDS(f[2]) else stop(fail, call. = FALSE)
+  if (wait) {
+    if (res == 0) readRDS(f[2]) else stop(
+      fail, if (file_exists(f[3])) c(': ', readRDS(f[3])) else '.', call. = FALSE
+    )
+  } else f
 }
 
 # call a function in a background process

inst/scripts/call-fun.R

@@ -1,11 +1,13 @@
-# This script is executed via the command line `Rscript call-fun.R arg1 arg2`,
-# where arg1 is a path to an .rds file, which contains the function and its
-# arguments saved as a list, and arg2 is a path to an .rds file to which the
-# returned value of the function call is saved.
+# This script is executed via the command line `Rscript call-fun.R arg1 arg2
+# arg3`, where arg1 is a path to an .rds file, which contains the function and
+# its arguments saved as a list; arg2 is a path to an .rds file to which the
+# returned value of the function call is saved; arg3 saves the error message.
 
 local({
-  if (length(a <- commandArgs(TRUE)) != 2)
-    stop('The number of arguments passed to Rscript should be 2.')
+  if (length(a <- commandArgs(TRUE)) != 3)
+    stop('The number of arguments passed to Rscript should be 3.')
+  # save the error message on exit if an error occurred
+  on.exit(if (!file.exists(a[2])) saveRDS(geterrmessage(), a[3]))
   x = readRDS(a[1])  # list(fun, args)
   f = x[[1]]
   if (is.character(f)) f = eval(parse(text = f), envir = globalenv())