Add Alchemy.config and DSL for type-safe configuration

[mamhoff]

What is this pull request for?

This adds a Ruby configuration parent class with a DSL for configuration objects. The intention is for this to replace the current use of parsed YAML files.

The disadvantages of the current system are

• Typos raise no errors
• Wrong types raise no errors
• We could put almost anything into the config file, and it would break nothing
• Configuration management involves merging big hashes
• Deprecations are hard, because Hash keys can't be deprecated

The configuration object in this PR offers the following DSL

class MyConfig < Alchemy::Configuration
  class AnotherConfig < Alchemy::Configuration
    option :level_1, :string, default: "ground_floor"
    option :level_2, :string, default: "open_floor"
  end
  option :foo, :integer, default: 1
  option :foos, :integer_list, default: [1, 2]
  option :bar, :string, default: "string"
  option :bars, :string_list, default: %w(hello world)
  configuration :levels, AnotherConfig
end

This is equivalent to the following hash, and can indeed be initialized with it:

conf_hash = {
  foo: 1,
  foos: [1, 2],
  bar: "string",
  bars: ["hello", "world"],
  levels: {
    level_1: "ground_floor",
    level_2: "open_floor",
  }
}
myconfig = MyConfig.new(conf_hash)

Parts of the configuration can be set later on, via Ruby or via a Hash:

myconfig.set(bar: "Actually a bar")
myconfig.bars = ["The", "bar", "district"]
myconfig.levels.level_1 = "garden"

Trying to set an option that has not been defined before will raise an NoMethodError.
Trying to set an option with data that does not have the right type will raise a TypeError.

With this change, default configuration options are now located in Alchemy's lib folder, so we don't have a default config.yml file anymore. I've removed it in this PR, because it's likely going to go stale soon (defaults change, and so on).

New users will get a generated alchemy.rb file, but the existing config.yml files will continue to work with no deprecation messages for now.

Alchemy.configure do |config|
  config.auto_logout_time = 45
end

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[codecov]

Codecov Report

Attention: Patch coverage is 99.67105% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.69%. Comparing base (d2cf3f4) to head (19f2f7c).
Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/alchemy/configuration/base_option.rb	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3178      +/-   ##
==========================================
+ Coverage   96.59%   96.69%   +0.10%     
==========================================
  Files         237      256      +19     
  Lines        6380     6606     +226     
==========================================
+ Hits         6163     6388     +225     
- Misses        217      218       +1     

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[mamhoff]

Codeclimate is not right. Abstracting that out would create an indirection that will be hard to read. The metaprogramming here is not so easy as-is.

[tvdeyen]

Nice. Thanks