docs: [FC-0074] add suggestion about the design of filters

[mariajgrimaldi]

Description

This PR adds an ADR with practices to consider when designing a filter and contributing it back to the library to be maintained as part of the framework. I'm proposing that these practices be considered when implementing new filters, but they should NOT be considered standards that all filters should strictly follow. Also, I'm not saying either that all the existing filters in the library comply (or should) with these practices.

This document will be used as a reference in the How to Create a New Filter guide. I'm currently validating these items while I write the guide, making sure these suggestions are clear enough to follow. You can review it here (consider that is still a draft): #242

Testing instructions

You can review the docs here: https://docsopenedxorg--240.org.readthedocs.build/projects/openedx-filters/en/240/decisions/0007-filter-design-practices.html

Deadline

None

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• Upgrade the package in the Open edX platform requirements (if applicable)

[openedx-webhooks]

Thanks for the pull request, @mariajgrimaldi!

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[MaferMazu]

I like this PR.

I would suggest adding a code example to show how to apply the guidelines correctly. It could be a full example or an example for each section.

It is not a blocker, but I think it could improve the understanding of the guidelines. Also, we are referencing this ADR in the how-to documentation. What do you think @mariajgrimaldi?

Example:

Design Clarity and Understanding

• A filter should describe as accurately as possible what behavior intends to modify.
• A filter should have a clear and concise name that describes its purpose.
• Ensure that the triggering logic of the filter is consistent and narrow. It should only trigger when the conditions are met and cover all the cases that the filter should be applied with the minimum number of modifications.

Anti-pattern

# openedx-filters
class CertificateFilter(OpenEdxPublicFilter):
    """
    Custom class used to create certificate creation filters and its custom methods.
    """

Best practice

# openedx-filters
class CertificateCreationRequested(OpenEdxPublicFilter):
    """
    Custom class used to create certificate creation filters and its custom methods.
    """

# edx-platform
def _generate_certificate_task(user, course_key, enrollment_mode, course_grade, status=None, generation_mode=None,
                               delay_seconds=CERTIFICATE_DELAY_SECONDS):
    """
    Create a task to generate a certificate
    """
    log.info(f'About to create a regular certificate task for {user.id} : {course_key}')

    course_grade_val = _get_grade_value(course_grade)

    try:
        # .. filter_implemented_name: CertificateCreationRequested
        # .. filter_type: org.openedx.learning.certificate.creation.requested.v1
        user, course_key, enrollment_mode, status, course_grade, generation_mode = CertificateCreationRequested.run_filter(  # pylint: disable=line-too-long
            user=user,
            course_key=course_key,
            mode=enrollment_mode,
            status=status,
            grade=course_grade,
            generation_mode=generation_mode,
        )
    except CertificateCreationRequested.PreventCertificateCreation as exc:
        raise CertificateGenerationNotAllowed(str(exc)) from exc

[mariajgrimaldi]

@MaferMazu: That's a really good idea! I'll work on integrating some examples in the ADR independently from the how-to. I'll ping you once it's done. Thank you!

[mariajgrimaldi]

@MaferMazu: done, you can review the changes now. Thank you again for the suggestions!

[MaferMazu]

I think it would be better if we had the general example with his own section and referenced it in the guidelines that need a reference so as not to stick to the general example only in the first suggestion and have to return to that in the next ones. What do you think @mariajgrimaldi?

[mariajgrimaldi]

@MaferMazu: I'm not sure I understand your latest comment. Could you explain a bit further? Thanks for the patience!

[MaferMazu]

I proposed having a specific section for the example because, right now, it is inside one of the recommendations, and returning a particular recommendation to view the example doesn't seem in order.

Right now, we have the following:

Design Clarity and Understanding
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
<Example>

Contextual Information
~~~~~~~~~~~~~~~~~~~~~~
...
Consider the user login filter example above. The filter provides...

...

Error Handling
~~~~~~~~~~~~~~
...
Consider the user login filter example above...

The idea is to have something like:

Design Clarity and Understanding
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
Consider the `Example with Best Practices`_  ...

Contextual Information
~~~~~~~~~~~~~~~~~~~~~~
...
Consider the `Example with Best Practices`_ . The filter provides...

...

Example with Best Practices
~~~~~~~~~~~~~~~~~~~~~~~~
<Example>

Or having the example above.

The main idea is not to have the whole example we want to reference in a particular guideline.

In my first suggestion, I thought of an example for each section that needed it. But if we use one example as a reference throughout the document, it makes sense that it has its section and doesn't live in a particular one.

[mariajgrimaldi]

@MaferMazu: Thank you for the detailed explanation. However, I think adding a more detailed example here would remove the need for this PR to implement a filter that follows these practices. Do you think we'd still need the example having that how-to?

[MaferMazu]

My comment was about the location of the example, and you already addressed it.

This looks good to me. Thanks @mariajgrimaldi ✨

[felipemontoya]

I think the advice contained in this doc is solid and at the technical level everything looks correct to me.

Feel free to merge when the inlines are addressed.