Bug: Mechanism-2 of PR #372 does not work

[erikmd]

Related issue(s) or PR(s):

• Offer better protections against solution overwriting #372

Related project scope(s): Web UI

Related user(s):

• @erikmd
• @yurug

Bug description

The test triggering the dialog "A more recent answer exists on the server. Do you want to fetch the new version?" has false negatives and false positives.
Moreover, a click on "Fetch from server & overwrite" does not trigger a fetch from the backend.

To reproduce

Steps to reproduce the behavior:

1. Run a local instance of Learn-OCaml (where the timing 180s is replaced with 10s)
2. Browse http://localhost:8080 and open the same exercise in two different browsers
3. (in both Browsers) the Sync button should be grayed at first ("bug 0")
4. (in Browser 1) change the text then sync, wait for 10s
5. (in Browser 2) edit text → nothing happens (bug 1: false negative)
6. (in Browser 1) edit text → the dialog shows up (bug 2: false positive), click on Ignore
7. (in Browser 2) click on sync, wait for 10s
8. ((in Browser 1) click on sync, wait for 10s) (optional)
9. (in Browser 2) edit text → the dialog shows up
10. (in Browser 2) click on Fetch from server & overwrite → same code of Browser 2 (bug 3: no fetch)

Expected behavior

• Fix the three bugs above and/or disable the timer logic and the automatic check.
• Make it possible to do a fetch on demand (without waiting for 180s), along with Feature: Expose more easily last the two versions of a saved exercise #493.

Current configuration

• OS name (and version): GNU/Linux
• Browser name (and version): Firefox and Chromium
• learn-ocaml --version: 0.14.0
• git describe --long --always --abbrev=40 --tags: v0.14.0-14-g9bc28a63ab13986dab36c9843142094b05ab5856

Additional context

The 1st and 3rd bug crept into master despite the testing of #372 certainly because this testing only involved two tabs of the same browser (with a common local storage…)