RSpec documentation without executing

main.rb

require 'syntax_tree'

class RSpecEnvironment
  def initialize
    @contexts = []
    @results = []
  end

  def klass(k)
    @contexts << k
  end

  def method(m)
    @contexts << m
  end

  def context(c)
    @contexts << c
  end
  alias describe context

  def decontext
    @contexts.pop
  end

  def it(i)
    indendted_context = @contexts.map.with_index { |c, i| '  ' * i + c }.join("\n")
    it_content = "#{'  ' * @contexts.size}it #{i}"
    @results << "#{indendted_context}\n#{it_content}"
  end

  def inspect
    @results.join("\n")
  end
end

class RSpecVisitor < SyntaxTree::Visitor
  attr_reader :environment

  def initialize
    super
    @environment = RSpecEnvironment.new
  end

  visit_methods do
    def visit_command_call(node)
      if node.receiver.child_nodes.first&.value == 'RSpec' && node.message.value == 'describe'
        @environment.klass node.arguments.child_nodes.first.child_nodes.first.value
      elsif node.receiver.message.value == 'expect'
        subject = node.receiver.arguments.arguments.parts.first.value.value
        predicate = node.arguments.parts.first.value.value
        @environment.it "expect #{subject} to #{predicate}"
      end
      super
    end

    def visit_command(node)
      name = node.child_nodes.first.value
      if name == 'describe' || name == 'context'
        str = node.arguments.child_nodes.first.parts.first.value
        if str.start_with?('#')
          @environment.method str
        else
          @environment.context str
        end
      elsif name == 'it'
        str = node.arguments.child_nodes.first.parts.first.value
        @environment.it str
      end
      super
      if name == 'describe' || name == 'context'
        @environment.decontext
      end
    end
  end
end

visitor = RSpecVisitor.new
visitor.visit(SyntaxTree.parse(SyntaxTree.read('sample_spec.rb')))
p visitor.environment

result.txt

Sample
  #sample
    with a context
      it works
Sample
  #sample
    with a context
      it expect true to be_truthy
Sample
  #foo
    some context
      it expect true to be_truthy
Sample
  #foo
    outside context
      inside context
        it expect obj to be_falsey

sample_spec.rb

RSpec.describe Sample do
  describe '#sample' do
    context 'with a context' do
      subject { 'subject' }
      let(:a) { 'a' }
      let(:b) { 'b' }
      it 'works' do
        expect(true).to be_truthy
      end
    end
  end
  describe '#foo' do
    subject { 1.abs }
    context 'some context' do
      subject { 'overridden subject' }
      it do
        expect(true).to be_truthy
      end
    end

    context 'outside context' do
      context 'inside context' do
        let(:obj) { Object.new }
        it do
          expect(obj).to be_falsey
        end
      end
    end
  end
end