lint(track_config): warn for empty practices and Practice Exercise prereqs

[ee7]

With this PR, configlet lint now checks that a track-level
config.json file follows the below rules:

• The exercises.practice[].practices value must be a non-empty array
  of strings if exercises.practice[].status is not equal to
  deprecated
• The exercises.practice[].prerequisites value must be a non-empty
  array of strings if exercises.practice[].status is not equal to
  deprecated

The checks are currently implemented as a warning. That is, a violation
does not by itself cause configlet to exit with a non-zero exit code.

---

@ErikSchierboom How should we approach this? Populating the values in these arrays is a lot of work, and many tracks don't even have concepts to populate them with. Should we maybe enable it as a warning only for tracks that set status.concept_exercises to true?

Currently this PR just prints the count, rather than each slug. I did this to reduce the verbosity, and because a maintainer probably fixes this by searching for "practices", not for each slug. But maybe printing the slugs makes more sense if we somehow warn only for tracks that have a small number of empty practices and Practice Exercise prerequisites.

One issue is that we might want a different timeline for these warnings than that shown in the current warning message:

Configlet produced at least one warning.
These warnings will become errors in a future configlet release (at the end of October 2021).

Aside: the proc that this PR touches now handles Concept and Practice Exercises differently enough that a combined proc doesn't help much to reduce duplication.

---

This PR currently produces the below diff to the output of configlet lint, per track:

babashka

+Warning: 76 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 75 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

bash

+Warning: 89 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 88 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

c

+Warning: 71 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 70 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

cfml

+Warning: 28 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 27 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

clojure

+Warning: 30 user-facing Practice Exercises have an empty `practices` array:
+./config.json

clojurescript

+Warning: 26 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 25 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

coffeescript

+Warning: 21 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 20 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

common-lisp

+Warning: 1 user-facing Practice Exercises have an empty `practices` array:
+./config.json

cpp

+Warning: 55 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 54 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

crystal

+Warning: 50 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 49 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

csharp

+Warning: 1 user-facing Practice Exercises have an empty `practices` array:
+./config.json

d

+Warning: 34 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 33 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

dart

+Warning: 37 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 36 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

delphi

+Warning: 76 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 75 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

elixir

+Warning: 5 user-facing Practice Exercises have an empty `practices` array:
+./config.json

elm

+Warning: 46 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 45 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

emacs-lisp

+Warning: 28 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 27 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

erlang

+Warning: 77 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 76 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

fortran

+Warning: 21 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 20 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

fsharp

+Warning: 14 user-facing Practice Exercises have an empty `practices` array:
+./config.json

gleam

+Warning: 5 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 4 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

go

+Warning: 109 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 108 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

groovy

+Warning: 55 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 54 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

haskell

+Warning: 96 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 95 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

java

+Warning: 114 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 113 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

javascript

+Warning: 107 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 83 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

julia

+Warning: 50 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 49 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

kotlin

+Warning: 84 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 83 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

lfe

+Warning: 31 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 30 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

lua

+Warning: 82 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 81 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

mips

+Warning: 15 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 14 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

nim

+Warning: 67 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 66 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

objective-c

+Warning: 51 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 50 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

ocaml

+Warning: 44 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 43 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

perl5

+Warning: 62 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 61 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

pharo-smalltalk

+Warning: 42 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 41 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

php

+Warning: 75 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 74 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

plsql

+Warning: 11 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 10 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

prolog

+Warning: 19 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 18 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

purescript

+Warning: 28 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 27 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

python

+Warning: 20 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 2 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

r

+Warning: 35 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 34 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

racket

+Warning: 33 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 32 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

raku

+Warning: 30 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 29 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

reasonml

+Warning: 24 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 23 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

ruby

+Warning: 3 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 1 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

rust

+Warning: 93 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 92 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

scala

+Warning: 91 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 90 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

scheme

+Warning: 39 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 38 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

shen

+Warning: 1 user-facing Practice Exercises have an empty `practices` array:
+./config.json

sml

+Warning: 27 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 26 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

swift

+Warning: 83 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 82 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

tcl

+Warning: 120 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 119 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

typescript

+Warning: 93 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 92 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

vbnet

+Warning: 13 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 12 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

vimscript

+Warning: 20 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 19 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

wren

+Warning: 19 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 51 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

x86-64-assembly

+Warning: 16 user-facing Practice Exercises have an empty `practices` array:
+./config.json
+
+Warning: 15 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

z3

+Warning: 1 user-facing Practice Exercises have an empty `prerequisites` array:
+./config.json

[ErikSchierboom]

How should we approach this? Populating the values in these arrays is a lot of work, and many tracks don't even have concepts to populate them with. Should we maybe enable it as a warning only for tracks that set status.concept_exercises to true?

I think only enabling this as a warning for tracks with .status.concept_exercises == true makes total sense. At some point we do want to have the practices field filled in for tracks with .status.concept_exercises == false, but that's a way off I think.

This is the current status of tracks with concept exercises:

clojure: 76 total, 0 no prerequisites
common-lisp: 43 total, 0 no prerequisites
csharp: 126 total, 0 no prerequisites
elixir: 118 total, 0 no prerequisites
elm: 46 total, 45 no prerequisites
fsharp: 123 total, 0 no prerequisites
go: 114 total, 108 no prerequisites
java: 120 total, 113 no prerequisites
javascript: 113 total, 84 no prerequisites
python: 129 total, 2 no prerequisites
ruby: 103 total, 1 no prerequisites
rust: 96 total, 92 no prerequisites
swift: 87 total, 82 no prerequisites

We plan on doing PRs to have at least some prerequisites for most tracks.