Merge branch 'master' into rc-v0.10.0

* master:
  Do not reset question submissions (#270)
  only display visible output in exercise (#268)

NEWS.md

@@ -21,6 +21,8 @@ learnr 0.10.0 (unreleased)
 
 * Missing package dependencies will ask to be installed at tutorial run time. (@isteves, [#253](https://github.com/rstudio/learnr/issues/253))
 
+* When questions are tried again, the existing answer will remain, not forcing the user to restart from scratch. ([#270](https://github.com/rstudio/learnr/issues/270))
+
 
 ## Bug fixes
 

R/exercise.R

@@ -237,15 +237,20 @@ evaluate_exercise <- function(exercise, envir) {
   #   only has one argument, only visible values are handled; if it has more
   #   arguments, the second argument indicates whether the value is visible.
   last_value <- NULL
+  last_value_is_visible <- TRUE
   default_output_handler <- evaluate::new_output_handler()
   has_visible_arg <- length(formals(default_output_handler$value)) > 1
   learnr_output_handler <- evaluate::new_output_handler(value = function(x, visible) {
     last_value <<- x
-
+    last_value_is_visible <<- visible
     if (has_visible_arg) {
       default_output_handler$value(x, visible)
     } else {
-      default_output_handler$value(x)
+      if (visible) {
+        default_output_handler$value(x)
+      } else {
+        invisible()
+      }
     }
   })
 
@@ -321,7 +326,8 @@ evaluate_exercise <- function(exercise, envir) {
     return(error_result("Error occured while parsing chunk option 'exercise.checker'."))
   }
 
-  if (is.null(exercise$check) || is.null(checker))
+  checker_fn_does_not_exist <- is.null(exercise$check) || is.null(checker)
+  if (checker_fn_does_not_exist)
     checker <- function(...) { NULL }
 
   # call the checker
@@ -348,14 +354,33 @@ evaluate_exercise <- function(exercise, envir) {
   feedback_validated(checker_feedback)
 
   # amend output with feedback as required
-  if (!is.null(checker_feedback)) {
-    feedback_html <- feedback_as_html(checker_feedback)
-    if (checker_feedback$location == "append")
+  feedback_html <-
+    if (!is.null(checker_feedback)) {
+      feedback_as_html(checker_feedback)
+    } else {
+      NULL
+    }
+
+  if (
+    # if the last value was invisible
+    !last_value_is_visible &&
+    # if the checker function exists
+    !checker_fn_does_not_exist
+  ) {
+    # works with NULL feedback
+    feedback_html <- htmltools::tagList(feedback_html, invisible_feedback())
+  }
+
+  if (!is.null(feedback_html)) {
+    # if no feedback, append invisible_feedback
+    feedback_location <- checker_feedback$location %||% "append"
+    if (feedback_location == "append") {
       html_output <- htmltools::tagList(html_output, feedback_html)
-    else if (checker_feedback$location == "prepend")
+    } else if (feedback_location == "prepend") {
       html_output <- htmltools::tagList(feedback_html, html_output)
-    else if (checker_feedback$location == "replace")
+    } else if (feedback_location == "replace") {
       html_output <- feedback_html
+    }
   }
 
   # return a list with the various results of the expression
@@ -380,6 +405,18 @@ error_result <- function(error_message) {
     html_output = error_message_html(error_message)
   )
 }
+invisible_feedback <- function() {
+  feedback_as_html(
+    feedback_validated(
+      list(
+        message = "Last value being used to check answer is invisible. See `?invisible` for more information",
+        type = "warning",
+        correct = FALSE,
+        location = "append"
+      )
+    )
+  )
+}
 
 timeout_error_message <- function() {
   paste("Error: Your code ran longer than the permitted time",

R/quiz.R

@@ -495,7 +495,10 @@ question_module_server_impl <- function(
     if (is.null(submitted_answer())) {
       # has not submitted, show regular answers
       return(
-        question_ui_initialize(question, submitted_answer())
+        # if there is an existing input$answer, display it.
+        # if there is no answer... init with NULL
+        # Do not re-render the UI for every input$answer change
+        question_ui_initialize(question, isolate(input$answer))
       )
     }
 
@@ -526,7 +529,10 @@ question_module_server_impl <- function(
   observeEvent(input$action_button, {
 
     if (button_type() == "try_again") {
-      init_question(NULL)
+      # maintain current submission / do not randomize answer order
+      # only reset the submitted answers
+      # does NOT reset input$answer
+      submitted_answer(NULL)
 
       # submit "reset" to server
       reset_question_submission_event(