`allow_skip: false` allows next section on empty console

[gaelso]

Issue

Current behavior of learnr exercises with YAML progressive: true and allow_skip: false doesn't condition the access to a next section based on the code submitted.

When clicking Continue / Next topic before any interaction with the exercise, the following message appears:

You must complete the exercise in this section before continuing.

This is a bit misleading as clicking on the Run code button on any code or even on an empty console unlocks access to the next section.

I understand conditioning button behavior on code run in exercises chunks might be tricky, but it should at least check that users didn't just click Run code on an empty console.

Steps to reproduce

Initiate a basic learnr tutorial (with Rstudio: File > New file > R Markdown... > from Template > interactive tutorial).

Replace YAML:

---
output: learnr::tutorial
---

With

---
output: 
  learnr::tutorial:
    progressive: true
    allow_skip: false
---

Click Run code on the first exercise without typing any code in to mark the exercise as completed and unlock access to the next section.

Session info

learnr 0.10.1.9017 on Win10 machine

[gadenbuie]

Notes to myself as I look into this.

Whether or not a user can move forward in a section is determined by the logic in the continue button click event handler

learnr/inst/rmarkdown/templates/tutorial/resources/tutorial-format.js

Lines 181 to 192 in 9bc2a37

	// if the section has exercises and is not complete, don't skip - put up message
	if (section.exercises.length && !section.completed && !section.allowSkip) {
	var exs = i18next.t(
	['text.exercise', 'exercise'],
	{count: section.exercises.length, lngs: [i18nextLang(), 'en']}
	);
	var youmustcomplete = i18next.t(['text.youmustcomplete', 'You must complete the']);
	var inthissection = i18next.t(['text.inthissection', 'in this section before continuing.']);
	bootbox.setLocale(i18nextLang());
	bootbox.alert(youmustcomplete + " " + exs + " " + inthissection);
	}

The section completed state seems to originate from the call to $fireSectionCompleted() in $fireProgressEvent(), where it appears that any exercise_submission event sets progressEvent.completed = true for the exercise in question.

learnr/inst/lib/tutorial/tutorial.js

Lines 257 to 259 in 9bc2a37

	if (event == "exercise_submission") {
	// any progress event for an exercise is to complete only
	progressEvent.completed = true;

Unfortunately, at this point, we don't know anything about the user's submission. In theory, the data given to this method has a label and correct flag —

{
  "label": "two-plus-two",
  "correct": true
}

— but the correct flag is true by default when the code isn't checked, as in above (why not null or undefined??)

learnr/R/events_default.R

Lines 139 to 142 in 9bc2a37

	if (data$checked)
	correct <- data$feedback$correct
	else
	correct <- TRUE

So it seems the lifecycle here is

1. User click run button
2. Shiny receives data, broadcasts an exercise_submission event that corresponds to an exercise_result event (since exercise_submission event was renamed in Separate exercise events, add additional metadata #337 but was apparently kept around in the JS)
3. The progress event handler ($fireProgressEvent()) sets the exercise as completed because we got the exercise_submission event
4. The section unlocks because the exercise is complete.

After writing this out, I'm going to start by testing:

1. Only set correct when submission doesn't require a check
2. Add completed to the data that is TRUE when there is submission code and
   • the exercise doesn't have any grading
   • OR the exercise has grading code and the exercise was checked
3. Update the progress event handling to use this completed flag to set as completed if not yet complete

[gadenbuie]

Fixed by #633