Add local_restore_options() function which *actually* restores `opt…

…ions()` and envvars, including `NULL` and `""`, to their original state on exit

R/exercise.R

@@ -287,8 +287,7 @@ evaluate_exercise <- function(
   exercise, envir, evaluate_global_setup = FALSE, data_dir = NULL
 ) {
   # Protect global options and environment vars from permanent modification
-  withr::local_options(list())
-  withr::local_envvar(as.list(Sys.getenv()))
+  local_restore_options()
 
   # adjust exercise version to match the current learnr version
   exercise <- upgrade_exercise(
@@ -439,8 +438,7 @@ get_checker_func <- function(exercise, name, envir) {
 
 render_exercise <- function(exercise, envir) {
   # Protect global options and environment vars from modification by student
-  withr::local_options(list())
-  withr::local_envvar(as.list(Sys.getenv()))
+  local_restore_options()
 
   # Make sure exercise (& setup) chunk options and code are prepped for rendering
   exercise <- prepare_exercise(exercise)
@@ -794,6 +792,27 @@ merge_options <- function(preserved_opts, inherited_opts, static_opts = list())
   opts[!grepl("^exercise", names(opts))]
 }
 
+local_restore_options <- function(.local_envir = parent.frame()) {
+  options <- options()
+  withr::defer(restore_options(options), envir = .local_envir)
+
+  envvars <- Sys.getenv()
+  withr::defer(restore_envvars(envvars), envir = .local_envir)
+}
+
+restore_options <- function(old) {
+  current    <- options()
+  nulls      <- setdiff(names(current), names(old))
+  old[nulls] <- list(NULL)
+  options(old)
+}
+
+restore_envvars <- function(old) {
+  current <- Sys.getenv()
+  nulls   <- setdiff(names(current), names(old))
+  Sys.unsetenv(nulls)
+  do.call(Sys.setenv, as.list(old))
+}
 
 #' An Exercise Checker for Debugging
 #'