Add linter

[johan-ejstrud]

@dsvedberg changed formatting of a file in 6b953d3 (#462)

The project should probably use a linter to align formats:

• Add linter which contributors can run locally
• Run same linter as part of GitHub Workflows, and fail PRs that doesn't comply
• Update formatting of all files in project

[dsvedberg]

@johan-ejstrud I use Visual Studio Code and the R extension, which runs the 'lintr' package. It can be used locally to lint an entire package as well as a GitHub Action in a workflow. Unfortunately I don't have experience setting up in a workflow though...

If you are not already using it, a formatter is helpful to resolve many of the formatting-related lints. Formatting before PRs helps avoid non-functional changes. If you already use a formatter with a custom style guide, it should be available to contributors as well!

[johan-ejstrud]

@dsvedberg sounds great. I've created a PR #465 and added the workflow.

It turned out that the lintr already had a suggested GitHub workflow on their continuous integration page, so I just added that, and made it a requirement, that this check passes before a PR merges.

Because I haven't used a linter for this project, this workflow now fails spectacularly. Do you want to have a go at running lintr on all files in the repo, so we can get the check to pass? I imagine we just have one massive "format with lintr" commit thats changes formatting, but no functionality, across all files.

Also, as you might have seen, @larpSTATGL agreed that we should add you as a contributor on GitHub, so I think you should now be able to create PRs directly in this repo, rather than from your own fork.

[dsvedberg]

I'll have a go!

However, there are certain styling options that you need to guide me on. I'll configure lintr and style-r to conform to this, formatting with style-r should then hopefully resolve all lints.

By default, lintr conforms to the tidyverse style guide.

Most of the lints in the package seems to be related to the following "issues" (might add as I work through the files):

Pipe operator
Default is to use the base pipe |>, not magrittr's %>% pipe.

Line lengths
Default line length is 80 characters.

Snake case
Variable and function names should only be snake case (i.e., contain lowercase letters, underscores and numbers)

Implicit return behaviour
Default is that return style should be implicit.

Should I keep default options or do you have a different preference?

[johan-ejstrud]

Awesome!

I do have opinions on formatting, but I'll waive them for an easy workflow.

I'm sure the Tidyverse people thought well and hard about this, so the defaults in lintr are probably great. Let's use them.

There are some cases where the Tidyverse pipe work differently from the base pipe, but I don't think we have any in the package, so it should be safe to switch, and if not, the tests will catch us.