fix: load mlr3 packages of the main session on the worker (#1189)

* fix: load mlr3 packages of the main session on the worker

* ...

Author: be-marc

NEWS.md

@@ -1,5 +1,8 @@
 # mlr3 (development version)
 
+* fix: The `mlr_reflections` were broken when an extension package was not loaded on the workers.
+  Extension packages must now register themselves in the `mlr_reflections$loaded_packages` field.
+
 # mlr3 0.21.0
 
 * BREAKING CHANGE: Deprecated `data_format` and `data_formats` for `Learner`, `Task`, and `DataBackend` classes.

R/helper_exec.R

@@ -35,7 +35,7 @@ future_map = function(n, FUN, ..., MoreArgs = list()) {
     lg$debug("Running resample() via future with %i iterations", n)
     future.apply::future_mapply(
       FUN, ..., MoreArgs = MoreArgs, SIMPLIFY = FALSE, USE.NAMES = FALSE,
-      future.globals = FALSE, future.packages = "mlr3", future.seed = TRUE,
+      future.globals = FALSE, future.packages = mlr_reflections$loaded_packages, future.seed = TRUE,
       future.scheduling = scheduling, future.chunk.size = chunk_size, future.stdout = stdout
     )
   }

R/mlr_reflections.R

@@ -8,6 +8,8 @@
 #' This environment be modified by third-party packages, e.g. by adding information about new task types
 #' or by extending the set of allowed feature types.
 #'
+#' Third-party packages that modify the reflections must register themselves in the `loaded_packages` field.
+#'
 #' The following objects are set by \CRANpkg{mlr3}:
 #'
 #' * `task_types` (`data.table()`)\cr
@@ -153,6 +155,9 @@ local({
   ### Logger
   mlr_reflections$loggers = list()
 
-  ### cache package version
+  ### Cached package version
   mlr_reflections$package_version = packageVersion("mlr3")
+
+  ### Loaded packages
+  mlr_reflections$loaded_packages = "mlr3"
 })