refactor(Gemfile): Simplify rails loading

The `RAILS_SOURCE` env was not documented, and the methods were
not up-to-date (and crashing). I think this is not necessary as
we can manually change the `gem` specification for testing. I
added a related comment in the Gemfile.

`RAILS_VERSION` has basically the same problem: we can manually
change the tag if we need to make a specific test.

As the code to fetch the latest version of Rails wasn't working
anymore, I changed it to something more robust, taking advantage
of the `Gem::Version` and `Gem::Requirement` classes. And without
relying on `eval`

Author: BuonOmo

CONTRIBUTING.md

@@ -90,12 +90,6 @@ To run a specific test case, use minitest's `-n` option to run tests that match
 TEST_FILES="test/cases/adapter_test.rb" TESTOPTS=`-n=/test_indexes/` bundle exec rake test
 ```
 
-By default, tests will be run from the bundled version of Rails. To run against a local copy, set environemnt variable `RAILS_SOURCE`. Running against a local copy of Rails can be helpful when try to debug issues.
-
-```bash
-RAILS_SOURCE="path/to/local_copy" bundle exec rake test
-```
-
 `test/config.yml` assumes CockroachDB will be running at localhost:26257 with a root user. Make changes to `test/config.yml` as needed.
 
 ### Run Tests from a Backup

Gemfile

@@ -1,58 +1,49 @@
-require 'openssl'
-source 'https://rubygems.org'
-gemspec
+# frozen_string_literal: true
 
-if ENV['RAILS_SOURCE']
-  gemspec path: ENV['RAILS_SOURCE']
-else
-  def get_version_from_gemspec
-    gemspec = eval(File.read('activerecord-cockroachdb-adapter.gemspec'))
+source "https://rubygems.org"
 
-    gem_version = gemspec.dependencies.
-      find { |dep| dep.name == 'activerecord' }.
-      requirement.
-      requirements.
-      first.
-      last
+gemspec
 
-    major, minor, tiny, pre = gem_version.segments
 
-    if pre
-      gem_version.to_s
-    else
-      find_latest_matching_version(major, minor)
+module RailsTag
+  class << self
+    def call
+      req = gemspec_requirement
+      "v" + all_activerecord_versions.find { req.satisfied_by?(_1) }.version
     end
-  end
 
-  def find_latest_matching_version(gemspec_major, gemspec_minor)
-    all_activerecord_versions.
-      reject { |version| version["prerelease"] }.
-      map { |version| version["number"].split(".").map(&:to_i) }.
-      find { |major, minor|
-        major == gemspec_major && (minor == gemspec_minor || gemspec_minor.nil?)
-      }.join(".")
-  end
+    def gemspec_requirement
+      File
+        .foreach("activerecord-cockroachdb-adapter.gemspec", chomp: true)
+        .find { _1[/add_dependency\s.activerecord.,\s.(.*)./] }
+
+      Gem::Requirement.new(Regexp.last_match(1))
+    end
 
-  def all_activerecord_versions
-    require 'net/http'
-    require 'yaml'
+    def all_activerecord_versions
+      require 'net/http'
+      require 'yaml'
 
-    uri = URI.parse "https://rubygems.org/api/v1/versions/activerecord.yaml"
-    http = Net::HTTP.new(uri.host, uri.port)
-    http.use_ssl = true
-    http.verify_mode = OpenSSL::SSL::VERIFY_NONE
+      uri = URI.parse "https://rubygems.org/api/v1/versions/activerecord.yaml"
+      http = Net::HTTP.new(uri.host, uri.port)
+      http.use_ssl = true
+      http.verify_mode = OpenSSL::SSL::VERIFY_NONE
 
-    YAML.load(
-      http.request(Net::HTTP::Get.new(uri.request_uri)).body
-    )
+      YAML.load(
+        http.request(Net::HTTP::Get.new(uri.request_uri)).body
+      ).map { Gem::Version.new(_1["number"]) }
+    end
   end
-
-  # Get Rails from source because the gem doesn't include tests
-  version = ENV['RAILS_VERSION'] || get_version_from_gemspec
-  gem 'rails', git: "https://github.com/rails/rails.git", tag: "v#{version}"
 end
 
-group :development do
+
+group :development, :test do
+  # We need to load the gem from git to have access to activerecord's test files.
+  # You can use `path: "some/local/rails"` if you want to test the gem against
+  # a specific rails codebase.
+  gem "rails", github: "rails/rails", tag: RailsTag.call
+
+  gem "rake"
   gem "byebug"
   gem "minitest-excludes", "~> 2.0.1"
 

activerecord-cockroachdb-adapter.gemspec

@@ -1,9 +1,6 @@
-# coding: utf-8
+# frozen_string_literal: true
 
-lib = File.expand_path('lib', __dir__)
-$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
-
-require './lib/version.rb'
+require_relative 'lib/version'
 version = ActiveRecord::COCKROACH_DB_ADAPTER_VERSION
 
 Gem::Specification.new do |spec|