Clarify vers representation of Elixir `~>` range with pre-release semantics

[maennchen]

In Elixir, SemVer version requirements may use the ~> operator.

Examples (naive translation):

• ~> 0.1 → >= 0.1.0, < 1.0.0
• ~> 0.1.5 → >= 0.1.5, < 0.2.0

Ref: https://hexdocs.pm/elixir/Version.html#module-requirements

However, because pre-release versions (e.g. -alpha, -beta, etc.) are ordered before their corresponding release version, these translations are not accurate.

Example:

iex> Version.match?("0.2.0-alpha.7", "~> 0.1.5")
false

iex> Version.match?("0.2.0-alpha.7", ">= 0.1.5 and <= 0.2.0")
true

iex> Version.compare("0.2.0-alpha.7", "0.2.0")
:lt

Therefore:

~> 0.1.5 ≠ >= 0.1.5, < 0.2.0

How should ~> be represented in vers, considering pre-release ordering semantics?

I believe this also affects the ^ operator in NPM:

vers-spec/tests/npm_range_from_native_test.json

Lines 1874 to 1883 in 470128d

	{
	"description": "Construct VERS range from native npm range.",
	"test_group": "advanced",
	"test_type": "from_native",
	"input": {
	"native_range": "^2.0.18 || ^3.0.16 || ^3.1.6 || ^4.0.8 || ^5.0.0-beta.5",
	"scheme": "npm"
	},
	"expected_output": "vers:npm/>=2.0.18|<3.0.0|>=3.0.16|>=3.1.6|<4.0.0|<4.0.0|>=4.0.8|>=5.0.0-beta.5|<5.0.0|<6.0.0"
	},

[pombredanne]

Some references as Ruby has a similar operator:

• https://github.com/ruby/ruby/blob/master/lib/rubygems/requirement.rb
• RubyGems provides a shortcut for this, commonly known as the twiddle-wakka https://guides.rubygems.org/patterns/
• https://web.archive.org/web/20170403015713/https://robots.thoughtbot.com/rubys-pessimistic-operator
• https://web.archive.org/web/20110102182351/https://robots.thoughtbot.com/post/2508037841/twiddle-wakka