Style Guide

It would be good if our contributors can follow the following style.

1. If possible, please use an editor that respects .editorconfig. But unfortunately, RStudio is not among them. But it boils down to just one rule: use 4 spaces for indentation. Why? "Mickey Mouse has four fingers, not two."

2. Use the GNU style aka Tidyverse style of parentheses, add spaces around infix operators, add a space after comma

.query_mirror_validity <- function(mirror) {
    if (mirror == "https://cran.r-project.org/") {
        return(TRUE)
    }
    all_mirrors <- utils::getCRANmirrors()$URL
    mirror %in% all_mirrors
}

.insert_materials_dir <- function(dockerfile_content) {
    dockerfile_content$COPY <- append(dockerfile_content$COPY, "COPY materials/ ./materials/")
    dockerfile_content
}

Why? Your code needs to breath (Actually, no. It's because the editor used by the maintainer uses flycheck and lintr will mark code without those spaces).

3. All functions are verbs see #44 For helper functions, use these verbs as suggestions

• .query_ (get information online)
• .extract_ (get information locally)
• .group_ (a special type of .extract_ that groups information locally)
• .is_ (predicate function for local information, always returns TRUE/FALSE)
• .resolve_ (kind-of special function for vectorization of resolve)
• .generate_ (generate something)
• .insert_ (insert things into Dockerfile)
• .cache_ (cache)
• .normalize_ (normalize / coerce)
• .write_ (write content as a file)

Why? One reason: auto-completion; also it reduces our cognitive load to name things, one of the only two hard things in computer science.

4. Several nouns are created: rang, ranglet, pkgrefs, pkgs, source, handle, dep_df; most of them are documented in pkgref.R. Repeat here:

## we follow:
## https://r-lib.github.io/pkgdepends/reference/pkg_refs.html

## syntax of a ref: source::handle
## source can be: "cran", "github" (as of now)
## a `handle` indicates how the `package` is sourced from the `source`:
## if source == "cran", handle <- package name as per DESCRIPTION, e.g. "rtoot"
## if source == "github", handle <- username/reponame, e.g. "schochastics/rtoot"

## Similar to pak::pak()
## `pkgs` parameter of resolve() can either be shorthands (e.g. "rtoot", "schochastics/rtoot")
## or pkgrefs (e.g. "cran::rtoot", "github::schochastics/rtoot")

## For `dep_df`
## compulsory columns
## `x`, `x_version`, `x_pubdate` are the information as per DESCRIPTION
## `x_pkgref` is x in pkgref, for internal storage, we don't use @ to indicate version / uid

## optional columns
## 1. if there are dependecies: `y`, `y_raw_version`, `type`, `y_pkgref`: as per DESCRIPTION; `y_raw_version` is not useful

## 2. for "github" (and possible "local" in the future)
## `x_uid` and `y_uid` are extra unique identifier for pinning down the package, if `?_version` isn't sufficient for this purpose
## if `source` == "github", `?_uid` <- "sha"

## `installation_order` should be an ordered data.frame
## not using snake case in column names for backward compatibility in containers, and not needed
## columns: x, version, source, handle, uid