doc: document nullptr comparisons in style guide

[addaleax]

This documents existing practices.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

[nodejs-github-bot]

@addaleax build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/1326/pipeline

[refack]

I thought we agreed to adopt the C++ Core Guidelines exactly to close the omissions in the style guide, and have explicit and well reasoned guidelines.
So this is change the current guideline ES.87: Don’t add redundant == or != to conditions to the opposite.

Could you provide reasons for this change?

[addaleax]

Could you provide reasons for this change?

What is says in the PR description. It documents what we currently have. Preferring to document existing style before working on changes was also what was echoed as a sentiment in the last TSC meeting.

I thought we agreed to adopt the C++ Core Guidelines exactly to close the omissions in the style guide, and have explicit and well reasoned guidelines.

We agreed to link these documents since they provide meaningful guidelines. They do not match our current style in all cases; for those cases, we have this very document.

[cjihrig]

For consistency, maybe make this if (foo != nullptr) and if (!foo).

[addaleax]

@cjihrig yup, done!

[refack]

I would like to ask for a reference for where this guideline came from, and what is it's reasoning.

[addaleax]

@refack This is, as the PR says, an existing practice that we follow. I can only speculate about the reasons why it was introduced, but it does follow the general “explicit is better than implicit” rule, and makes clear whether a check tests a pointer or a boolean.

The origins of the rule definitely predate my time around here (and I’m not so sure about their relevance). @bnoordhuis might know.

[danbev]

Landed in 24cb1f3.