fix(teacher_tab): partly fix Open/Close handling w.r.t. Assignments

[erikmd]

• Kind: bugfix
• Close #534
• Related: #558

Description

• Refactor "Open"/"OpenAssg"… display code, Add functions in Learnocaml_data rather than in the js_of_ocaml code
• Make invariants explicit in OCaml comments
• Add unit tests using ppx_expect, ppx_inline_test

Checklist

• [x] Read the CONTRIBUTING.md guide and:
  • [x] Use Atomic Commits so each commit gathers a single logical change
  • [x] Use Conventional Commits regarding commit messages (needed by our release toolchain)
• [x] Add/update tests
• [ ] Add/update documentation
• [ ] …

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[erikmd]

Summary of the telco with @yurug → ideally, we'd want:

• [x] 1. a bit more doc (ocaml docstrings)
• [x] 2. a check predicate to check an assignments value
• [x] 3. a check_and_fix function to replace all spurious Open with Close
• [ ] 4. a runtime test (learn-ocaml serve) that calls the check predicate and fails noisily if need be
• [ ] 5. a CLI option that calls the check_and_fix function
• [x] 6. unit tests that exercise these functions in a few corner cases (using https://opam.ocaml.org/packages/ppx_inline_test/ or https://opam.ocaml.org/packages/ppx_expect/)

as the feature addressed by this PR is critical for learn-ocaml.

Regarding items 4. 5. → see my upcoming comment.

[erikmd]

@AltGr @yurug the PR is ready! except for the static builds failure (cf. this discuss thread)

FYI, to follow-up the previous comment:

On second thought, I didn't add a blocking runtime test (which could be distracting for end users), and improved the teacher tab instead to ensure the Inconsistency is displayed, and fixed on the next click on Open/Close.

See the following screenshots.

Opening the teacher tab after loading the inconsistent sync.zip from #558

After clicking on Open/Close for all exercises

[erikmd]

Good news, the CI issue is now fixed.

Note: there's still an issue in learnocaml_teacher_tab.ml (among those spotted in #558)

Will fix this ASAP in a later PR.

[yurug]

LGTM