Import spec examples from ruby/syntax_suggest

Merged: https://github.com/ruby/ruby/pull/6287

spec/syntax_suggest/fixtures/derailed_require_tree.rb.txt

@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+# Tree structure used to store and sort require memory costs
+# RequireTree.new('get_process_mem')
+module DerailedBenchmarks
+  class RequireTree
+    REQUIRED_BY = {}
+
+    attr_reader   :name
+    attr_writer   :cost
+    attr_accessor :parent
+
+    def initialize(name)
+      @name     = name
+      @children = {}
+      @cost = 0
+
+    def self.reset!
+      REQUIRED_BY.clear
+      if defined?(Kernel::REQUIRE_STACK)
+        Kernel::REQUIRE_STACK.clear
+
+        Kernel::REQUIRE_STACK.push(TOP_REQUIRE)
+      end
+    end
+
+    def <<(tree)
+      @children[tree.name.to_s] = tree
+      tree.parent = self
+      (REQUIRED_BY[tree.name.to_s] ||= []) << self.name
+    end
+
+    def [](name)
+      @children[name.to_s]
+    end
+
+    # Returns array of child nodes
+    def children
+      @children.values
+    end
+
+    def cost
+      @cost || 0
+    end
+
+    # Returns sorted array of child nodes from Largest to Smallest
+    def sorted_children
+      children.sort { |c1, c2| c2.cost <=> c1.cost }
+    end
+
+    def to_string
+      str = String.new("#{name}: #{cost.round(4)} MiB")
+      if parent && REQUIRED_BY[self.name.to_s]
+        names = REQUIRED_BY[self.name.to_s].uniq - [parent.name.to_s]
+        if names.any?
+          str << " (Also required by: #{ names.first(2).join(", ") }"
+          str << ", and #{names.count - 2} others" if names.count > 3
+          str << ")"
+        end
+      end
+      str
+    end
+
+    # Recursively prints all child nodes
+    def print_sorted_children(level = 0, out = STDOUT)
+      return if cost < ENV['CUT_OFF'].to_f
+      out.puts "  " * level + self.to_string
+      level += 1
+      sorted_children.each do |child|
+        child.print_sorted_children(level, out)
+      end
+    end
+  end
+end

spec/syntax_suggest/fixtures/rexe.rb.txt

@@ -0,0 +1,569 @@
+#!/usr/bin/env ruby
+#
+# rexe - Ruby Command Line Executor Filter
+#
+# Inspired by https://github.com/thisredone/rb
+
+# frozen_string_literal: true
+
+
+require 'bundler'
+require 'date'
+require 'optparse'
+require 'ostruct'
+require 'shellwords'
+
+class Rexe
+
+  VERSION = '1.5.1'
+
+  PROJECT_URL = 'https://github.com/keithrbennett/rexe'
+
+
+  module Helpers
+
+    # Try executing code. If error raised, print message (but not stack trace) & exit -1.
+    def try
+      begin
+        yield
+      rescue Exception => e
+        unless e.class == SystemExit
+          $stderr.puts("rexe: #{e}")
+          $stderr.puts("Use the -h option to get help.")
+          exit(-1)
+        end
+      end
+    end
+  end
+
+
+  class Options < Struct.new(
+      :input_filespec,
+      :input_format,
+      :input_mode,
+      :loads,
+      :output_format,
+      :output_format_tty,
+      :output_format_block,
+      :requires,
+      :log_format,
+      :noop)
+
+
+    def initialize
+      super
+      clear
+    end
+
+
+    def clear
+      self.input_filespec = nil
+      self.input_format        = :none
+      self.input_mode          = :none
+      self.output_format       = :none
+      self.output_format_tty   = :none
+      self.output_format_block = :none
+      self.loads               = []
+      self.requires            = []
+      self.log_format          = :none
+      self.noop                = false
+    end
+  end
+
+
+
+
+
+  class Lookups
+    def input_modes
+      @input_modes ||= {
+          'l' => :line,
+          'e' => :enumerator,
+          'b' => :one_big_string,
+          'n' => :none
+      }
+    end
+
+
+    def input_formats
+      @input_formats ||=  {
+          'j' => :json,
+          'm' => :marshal,
+          'n' => :none,
+          'y' => :yaml,
+      }
+    end
+
+
+    def input_parsers
+      @input_parsers ||= {
+          json:    ->(string)  { JSON.parse(string) },
+          marshal: ->(string)  { Marshal.load(string) },
+          none:    ->(string)  { string },
+          yaml:    ->(string)  { YAML.load(string) },
+      }
+    end
+
+
+    def output_formats
+      @output_formats ||= {
+          'a' => :amazing_print,
+          'i' => :inspect,
+          'j' => :json,
+          'J' => :pretty_json,
+          'm' => :marshal,
+          'n' => :none,
+          'p' => :puts,         # default
+          'P' => :pretty_print,
+          's' => :to_s,
+          'y' => :yaml,
+      }
+    end
+
+
+    def formatters
+      @formatters ||=  {
+          amazing_print: ->(obj)  { obj.ai + "\n" },
+          inspect:       ->(obj)  { obj.inspect + "\n" },
+          json:          ->(obj)  { obj.to_json },
+          marshal:       ->(obj)  { Marshal.dump(obj) },
+          none:          ->(_obj) { nil },
+          pretty_json:   ->(obj)  { JSON.pretty_generate(obj) },
+          pretty_print:  ->(obj)  { obj.pretty_inspect },
+          puts:          ->(obj)  { require 'stringio'; sio = StringIO.new; sio.puts(obj); sio.string },
+          to_s:          ->(obj)  { obj.to_s + "\n" },
+          yaml:          ->(obj)  { obj.to_yaml },
+      }
+    end
+
+
+    def format_requires
+      @format_requires ||= {
+          json:          'json',
+          pretty_json:   'json',
+          amazing_print: 'amazing_print',
+          pretty_print:  'pp',
+          yaml:          'yaml'
+      }
+    end
+  end
+
+
+
+  class CommandLineParser
+
+    include Helpers
+
+    attr_reader :lookups, :options
+
+    def initialize
+      @lookups = Lookups.new
+      @options = Options.new
+    end
+
+
+    # Inserts contents of REXE_OPTIONS environment variable at the beginning of ARGV.
+    private def prepend_environment_options
+      env_opt_string = ENV['REXE_OPTIONS']
+      if env_opt_string
+        args_to_prepend = Shellwords.shellsplit(env_opt_string)
+        ARGV.unshift(args_to_prepend).flatten!
+      end
+    end
+
+
+    private def add_format_requires_to_requires_list
+      formats = [options.input_format, options.output_format, options.log_format]
+      requires = formats.map { |format| lookups.format_requires[format] }.uniq.compact
+      requires.each { |r| options.requires << r }
+    end
+
+
+    private def help_text
+      unless @help_text
+        @help_text ||= <<~HEREDOC
+
+          rexe -- Ruby Command Line Executor/Filter -- v#{VERSION} -- #{PROJECT_URL}
+
+          Executes Ruby code on the command line,
+          optionally automating management of standard input and standard output,
+          and optionally parsing input and formatting output with YAML, JSON, etc.
+
+          rexe [options] [Ruby source code]
+
+          Options:
+
+          -c  --clear_options        Clear all previous command line options specified up to now
+          -f  --input_file           Use this file instead of stdin for preprocessed input;
+                                     if filespec has a YAML and JSON file extension,
+                                     sets input format accordingly and sets input mode to -mb
+          -g  --log_format FORMAT    Log format, logs to stderr, defaults to -gn (none)
+                                     (see -o for format options)
+          -h, --help                 Print help and exit
+          -i, --input_format FORMAT  Input format, defaults to -in (None)
+                                       -ij  JSON
+                                       -im  Marshal
+                                       -in  None (default)
+                                       -iy  YAML
+          -l, --load RUBY_FILE(S)    Ruby file(s) to load, comma separated;
+                                       ! to clear all, or precede a name with '-' to remove
+          -m, --input_mode MODE      Input preprocessing mode (determines what `self` will be)
+                                     defaults to -mn (none)
+                                       -ml  line; each line is ingested as a separate string
+                                       -me  enumerator (each_line on STDIN or File)
+                                       -mb  big string; all lines combined into one string
+                                       -mn  none (default); no input preprocessing;
+                                            self is an Object.new
+          -n, --[no-]noop            Do not execute the code (useful with -g);
+                                     For true: yes, true, y, +; for false: no, false, n
+          -o, --output_format FORMAT Output format, defaults to -on (no output):
+                                       -oa  Amazing Print
+                                       -oi  Inspect
+                                       -oj  JSON
+                                       -oJ  Pretty JSON
+                                       -om  Marshal
+                                       -on  No Output (default)
+                                       -op  Puts
+                                       -oP  Pretty Print
+                                       -os  to_s
+                                       -oy  YAML
+                                       If 2 letters are provided, 1st is for tty devices, 2nd for block
+          --project-url              Outputs project URL on Github, then exits
+          -r, --require REQUIRE(S)   Gems and built-in libraries to require, comma separated;
+                                       ! to clear all, or precede a name with '-' to remove
+          -v, --version              Prints version and exits
+
+          ---------------------------------------------------------------------------------------
+
+          In many cases you will need to enclose your source code in single or double quotes.
+
+          If source code is not specified, it will default to 'self',
+          which is most likely useful only in a filter mode (-ml, -me, -mb).
+
+          If there is a .rexerc file in your home directory, it will be run as Ruby code
+          before processing the input.
+
+          If there is a REXE_OPTIONS environment variable, its content will be prepended
+          to the command line so that you can specify options implicitly
+          (e.g. `export REXE_OPTIONS="-r amazing_print,yaml"`)
+
+      HEREDOC
+
+        @help_text.freeze
+      end
+
+      @help_text
+    end
+
+
+    # File file input mode; detects the input mode (JSON, YAML, or None) from the extension.
+    private def autodetect_file_format(filespec)
+      extension = File.extname(filespec).downcase
+      if extension == '.json'
+        :json
+      elsif extension == '.yml' || extension == '.yaml'
+        :yaml
+      else
+        :none
+      end
+    end
+
+
+    private def open_resource(resource_identifier)
+      command = case (`uname`.chomp)
+                when 'Darwin'
+                  'open'
+                when 'Linux'
+                  'xdg-open'
+                else
+                  'start'
+                end
+
+      `#{command} #{resource_identifier}`
+    end
+
+
+  # Using 'optparse', parses the command line.
+    # Settings go into this instance's properties (see Struct declaration).
+    def parse
+
+      prepend_environment_options
+
+      OptionParser.new do |parser|
+
+        parser.on('-c', '--clear_options', "Clear all previous command line options") do |v|
+          options.clear
+        end
+
+        parser.on('-f', '--input_file FILESPEC',
+            'Use this file instead of stdin; autodetects YAML and JSON file extensions') do |v|
+          unless File.exist?(v)
+            raise "File #{v} does not exist."
+          end
+          options.input_filespec = v
+          options.input_format = autodetect_file_format(v)
+          if [:json, :yaml].include?(options.input_format)
+            options.input_mode = :one_big_string
+          end
+        end
+
+        parser.on('-g', '--log_format FORMAT', 'Log format, logs to stderr, defaults to none (see -o for format options)') do |v|
+          options.log_format = lookups.output_formats[v]
+          if options.log_format.nil?
+            raise("Output mode was '#{v}' but must be one of #{lookups.output_formats.keys}.")
+          end
+        end
+
+        parser.on("-h", "--help", "Show help") do |_help_requested|
+          puts help_text
+          exit
+        end
+
+        parser.on('-i', '--input_format FORMAT',
+                  'Mode with which to parse input values (n = none (default), j = JSON, m = Marshal, y = YAML') do |v|
+
+          options.input_format = lookups.input_formats[v]
+          if options.input_format.nil?
+            raise("Input mode was '#{v}' but must be one of #{lookups.input_formats.keys}.")
+          end
+        end
+
+        parser.on('-l', '--load RUBY_FILE(S)', 'Ruby file(s) to load, comma separated, or ! to clear') do |v|
+          if v == '!'
+            options.loads.clear
+          else
+            loadfiles = v.split(',').map(&:strip).map { |s| File.expand_path(s) }
+            removes, adds = loadfiles.partition { |filespec| filespec[0] == '-' }
+
+            existent, nonexistent = adds.partition { |filespec| File.exists?(filespec) }
+            if nonexistent.any?
+              raise("\nDid not find the following files to load: #{nonexistent}\n\n")
+            else
+              existent.each { |filespec| options.loads << filespec }
+            end
+
+            removes.each { |filespec| options.loads -= [filespec[1..-1]] }
+          end
+        end
+
+        parser.on('-m', '--input_mode MODE',
+                  'Mode with which to handle input (-ml, -me, -mb, -mn (default)') do |v|
+
+          options.input_mode = lookups.input_modes[v]
+          if options.input_mode.nil?
+            raise("Input mode was '#{v}' but must be one of #{lookups.input_modes.keys}.")
+          end
+        end
+
+        # See https://stackoverflow.com/questions/54576873/ruby-optionparser-short-code-for-boolean-option
+        # for an excellent explanation of this optparse incantation.
+        # According to the answer, valid options are:
+        # -n no, -n yes, -n false, -n true, -n n, -n y, -n +, but not -n -.
+        parser.on('-n', '--[no-]noop [FLAG]', TrueClass, "Do not execute the code (useful with -g)") do |v|
+          options.noop = (v.nil? ? true : v)
+        end
+
+        parser.on('-o', '--output_format FORMAT',
+                  'Mode with which to format values for output (`-o` + [aijJmnpsy])') do |v|
+          options.output_format_tty   = lookups.output_formats[v[0]]
+          options.output_format_block = lookups.output_formats[v[-1]]
+          options.output_format = ($stdout.tty? ? options.output_format_tty : options.output_format_block)
+          if [options.output_format_tty, options.output_format_block].include?(nil)
+            raise("Bad output mode '#{v}'; each must be one of #{lookups.output_formats.keys}.")
+          end
+        end
+
+        parser.on('-r', '--require REQUIRE(S)',
+                  'Gems and built-in libraries (e.g. shellwords, yaml) to require, comma separated, or ! to clear') do |v|
+          if v == '!'
+            options.requires.clear
+          else
+            v.split(',').map(&:strip).each do |r|
+              if r[0] == '-'
+                options.requires -= [r[1..-1]]
+              else
+                options.requires << r
+              end
+            end
+          end
+        end
+
+        parser.on('-v', '--version', 'Print version') do
+          puts VERSION
+          exit(0)
+        end
+
+        # Undocumented feature: open Github project with default web browser on a Mac
+        parser.on('', '--open-project') do
+          open_resource(PROJECT_URL)
+          exit(0)
+        end
+
+        parser.on('', '--project-url') do
+          puts PROJECT_URL
+          exit(0)
+        end
+
+      end.parse!
+
+      # We want to do this after all options have been processed because we don't want any clearing of the
+      # options (by '-c', etc.) to result in exclusion of these needed requires.
+      add_format_requires_to_requires_list
+
+      options.requires = options.requires.sort.uniq
+      options.loads.uniq!
+
+      options
+
+    end
+  end
+
+
+  class Main
+
+    include Helpers
+
+    attr_reader :callable, :input_parser, :lookups,
+                :options, :output_formatter,
+                :log_formatter, :start_time, :user_source_code
+
+
+    def initialize
+      @lookups = Lookups.new
+      @start_time = DateTime.now
+    end
+
+
+    private def load_global_config_if_exists
+      filespec = File.join(Dir.home, '.rexerc')
+      load(filespec) if File.exists?(filespec)
+    end
+
+
+    private def init_parser_and_formatters
+      @input_parser     = lookups.input_parsers[options.input_format]
+      @output_formatter = lookups.formatters[options.output_format]
+      @log_formatter    = lookups.formatters[options.log_format]
+    end
+
+
+    # Executes the user specified code in the manner appropriate to the input mode.
+    # Performs any optionally specified parsing on input and formatting on output.
+    private def execute(eval_context_object, code)
+      if options.input_format != :none && options.input_mode != :none
+        eval_context_object = input_parser.(eval_context_object)
+      end
+
+      value = eval_context_object.instance_eval(&code)
+
+      unless options.output_format == :none
+        print output_formatter.(value)
+      end
+    rescue Errno::EPIPE
+      exit(-13)
+    end
+
+
+    # The global $RC (Rexe Context) OpenStruct is available in your user code.
+    # In order to make it possible to access this object in your loaded files, we are not creating
+    # it here; instead we add properties to it. This way, you can initialize an OpenStruct yourself
+    # in your loaded code and it will still work. If you do that, beware, any properties you add will be
+    # included in the log output. If the to_s of your added objects is large, that might be a pain.
+    private def init_rexe_context
+      $RC ||= OpenStruct.new
+      $RC.count         = 0
+      $RC.rexe_version  = VERSION
+      $RC.start_time    = start_time.iso8601
+      $RC.source_code   = user_source_code
+      $RC.options       = options.to_h
+
+      def $RC.i; count end  # `i` aliases `count` so you can more concisely get the count in your user code
+    end
+
+
+    private def create_callable
+      eval("Proc.new { #{user_source_code} }")
+    end
+
+
+    private def lookup_action(mode)
+      input = options.input_filespec ? File.open(options.input_filespec) : STDIN
+      {
+          line:           -> { input.each { |l| execute(l.chomp, callable);            $RC.count += 1 } },
+          enumerator:     -> { execute(input.each_line, callable);                     $RC.count += 1 },
+          one_big_string: -> { big_string = input.read; execute(big_string, callable); $RC.count += 1 },
+          none:           -> { execute(Object.new, callable) }
+      }.fetch(mode)
+    end
+
+
+    private def output_log_entry
+      if options.log_format != :none
+        $RC.duration_secs = Time.now - start_time.to_time
+        STDERR.puts(log_formatter.($RC.to_h))
+      end
+    end
+
+
+    # Bypasses Bundler's restriction on loading gems
+    # (see https://stackoverflow.com/questions/55144094/bundler-doesnt-permit-using-gems-in-project-home-directory)
+    private def require!(the_require)
+      begin
+        require the_require
+      rescue LoadError => error
+        gem_path = `gem which #{the_require}`
+        if gem_path.chomp.strip.empty?
+          raise error # re-raise the error, can't fix it
+        else
+          load_dir = File.dirname(gem_path)
+          $LOAD_PATH += load_dir
+          require the_require
+        end
+      end
+    end
+
+
+    # This class' entry point.
+    def call
+
+      try do
+
+        @options = CommandLineParser.new.parse
+
+        options.requires.each { |r| require!(r) }
+        load_global_config_if_exists
+        options.loads.each { |file| load(file) }
+
+        @user_source_code = ARGV.join(' ')
+        @user_source_code = 'self' if @user_source_code == ''
+
+        @callable = create_callable
+
+        init_rexe_context
+        init_parser_and_formatters
+
+        # This is where the user's source code will be executed; the action will in turn call `execute`.
+        lookup_action(options.input_mode).call unless options.noop
+
+        output_log_entry
+      end
+    end
+  end
+end
+
+
+def bundler_run(&block)
+  # This used to be an unconditional call to with_clean_env but that method is now deprecated:
+  # [DEPRECATED] `Bundler.with_clean_env` has been deprecated in favor of `Bundler.with_unbundled_env`.
+  # If you instead want the environment before bundler was originally loaded,
+  # use `Bundler.with_original_env`
+
+  if Bundler.respond_to?(:with_unbundled_env)
+    Bundler.with_unbundled_env { block.call }
+  else
+    Bundler.with_clean_env { block.call }
+  end
+end
+
+
+bundler_run { Rexe::Main.new.call }

spec/syntax_suggest/fixtures/routes.rb.txt

@@ -0,0 +1,121 @@
+Rails.application.routes.draw do
+  constraints -> { Rails.application.config.non_production } do
+    namespace :foo do
+      resource :bar
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+  constraints -> { Rails.application.config.non_production } do
+    namespace :bar do
+      resource :baz
+    end
+  end
+
+  namespace :admin do
+    resource :session
+
+  match "/foobar(*path)", via: :all, to: redirect { |_params, req|
+    uri = URI(req.path.gsub("foobar", "foobaz"))
+    uri.query = req.query_string.presence
+    uri.to_s
+  }
+end

spec/syntax_suggest/fixtures/this_project_extra_def.rb.txt

@@ -0,0 +1,64 @@
+module SyntaxErrorSearch
+  # Used for formatting invalid blocks
+  class DisplayInvalidBlocks
+    attr_reader :filename
+
+    def initialize(block_array, io: $stderr, filename: nil)
+      @filename = filename
+      @io = io
+      @blocks = block_array
+      @lines = @blocks.map(&:lines).flatten
+      @digit_count = @lines.last.line_number.to_s.length
+      @code_lines = @blocks.first.code_lines
+
+      @invalid_line_hash = @lines.each_with_object({}) {|line, h| h[line] = true}
+    end
+
+    def call
+      @io.puts <<~EOM
+
+        SyntaxSuggest: A syntax error was detected
+
+        This code has an unmatched `end` this is caused by either
+        missing a syntax keyword (`def`,  `do`, etc.) or inclusion
+        of an extra `end` line:
+      EOM
+
+      @io.puts(<<~EOM) if filename
+        file: #{filename}
+      EOM
+
+      @io.puts <<~EOM
+        #{code_with_filename}
+      EOM
+    end
+
+    def filename
+
+    def code_with_filename
+      string = String.new("")
+      string << "```\n"
+      string << "#".rjust(@digit_count) + " filename: #{filename}\n\n" if filename
+      string << code_with_lines
+      string << "```\n"
+      string
+    end
+
+    def code_with_lines
+      @code_lines.map do |line|
+        next if line.hidden?
+        number = line.line_number.to_s.rjust(@digit_count)
+        if line.empty?
+          "#{number.to_s}#{line}"
+        else
+          string = String.new
+          string << "\e[1;3m" if @invalid_line_hash[line] # Bold, italics
+          string << "#{number.to_s}  "
+          string << line.to_s
+          string << "\e[0m"
+          string
+        end
+      end.join
+    end
+  end
+end

spec/syntax_suggest/fixtures/webmock.rb.txt

@@ -0,0 +1,35 @@
+describe "webmock tests" do
+  before(:each) do
+    WebMock.enable!
+  end
+
+  after(:each) do
+    WebMock.disable!
+  end
+
+  it "port" do
+    port = rand(1000...9999)
+    stub_request(:any, "localhost:#{port}")
+
+    query = Cutlass::FunctionQuery.new(
+      port: port
+    ).call
+
+    expect(WebMock).to have_requested(:post, "localhost:#{port}").
+      with(body: "{}")
+  end
+
+  it "body" do
+    body = { lol: "hi" }
+    port = 8080
+    stub_request(:any, "localhost:#{port}")
+
+    query = Cutlass::FunctionQuery.new(
+      port: port
+      body: body
+    ).call
+
+    expect(WebMock).to have_requested(:post, "localhost:#{port}").
+      with(body: body.to_json)
+  end
+end

spec/syntax_suggest/integration/exe_cli_spec.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "exe" do
+    def exe_path
+      root_dir.join("exe").join("syntax_suggest")
+    end
+
+    def exe(cmd)
+      out = run!("#{exe_path} #{cmd}", raise_on_nonzero_exit: false)
+      puts out if ENV["SYNTAX_SUGGEST_DEBUG"]
+      out
+    end
+
+    it "prints the version" do
+      out = exe("-v")
+      expect(out.strip).to include(SyntaxSuggest::VERSION)
+    end
+  end
+end

spec/syntax_suggest/integration/ruby_command_line_spec.rb

@@ -0,0 +1,151 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "Requires with ruby cli" do
+    it "namespaces all monkeypatched methods" do
+      Dir.mktmpdir do |dir|
+        tmpdir = Pathname(dir)
+        script = tmpdir.join("script.rb")
+        script.write <<~'EOM'
+          puts Kernel.private_methods
+        EOM
+
+        syntax_suggest_methods_file = tmpdir.join("syntax_suggest_methods.txt")
+        api_only_methods_file = tmpdir.join("api_only_methods.txt")
+        kernel_methods_file = tmpdir.join("kernel_methods.txt")
+
+        d_pid = Process.spawn("ruby -I#{lib_dir} -rsyntax_suggest #{script} 2>&1 > #{syntax_suggest_methods_file}")
+        k_pid = Process.spawn("ruby #{script} 2>&1 >> #{kernel_methods_file}")
+        r_pid = Process.spawn("ruby -I#{lib_dir} -rsyntax_suggest/api #{script} 2>&1 > #{api_only_methods_file}")
+
+        Process.wait(k_pid)
+        Process.wait(d_pid)
+        Process.wait(r_pid)
+
+        kernel_methods_array = kernel_methods_file.read.strip.lines.map(&:strip)
+        syntax_suggest_methods_array = syntax_suggest_methods_file.read.strip.lines.map(&:strip)
+        api_only_methods_array = api_only_methods_file.read.strip.lines.map(&:strip)
+
+        # In ruby 3.1.0-preview1 the `timeout` file is already required
+        # we can remove it if it exists to normalize the output for
+        # all ruby versions
+        [syntax_suggest_methods_array, kernel_methods_array, api_only_methods_array].each do |array|
+          array.delete("timeout")
+        end
+
+        methods = (syntax_suggest_methods_array - kernel_methods_array).sort
+        if methods.any?
+          expect(methods).to eq(["syntax_suggest_original_load", "syntax_suggest_original_require", "syntax_suggest_original_require_relative"])
+        end
+
+        methods = (api_only_methods_array - kernel_methods_array).sort
+        expect(methods).to eq([])
+      end
+    end
+
+    it "detects require error and adds a message with auto mode" do
+      Dir.mktmpdir do |dir|
+        tmpdir = Pathname(dir)
+        script = tmpdir.join("script.rb")
+        script.write <<~EOM
+          describe "things" do
+            it "blerg" do
+            end
+
+            it "flerg"
+            end
+
+            it "zlerg" do
+            end
+          end
+        EOM
+
+        require_rb = tmpdir.join("require.rb")
+        require_rb.write <<~EOM
+          load "#{script.expand_path}"
+        EOM
+
+        out = `ruby -I#{lib_dir} -rsyntax_suggest #{require_rb} 2>&1`
+
+        expect($?.success?).to be_falsey
+        expect(out).to include('❯  5    it "flerg"').once
+      end
+    end
+
+    it "annotates a syntax error in Ruby 3.2+ when require is not used" do
+      pending("Support for SyntaxError#detailed_message monkeypatch needed https://gist.github.com/schneems/09f45cc23b9a8c46e9af6acbb6e6840d?permalink_comment_id=4172585#gistcomment-4172585")
+
+      skip if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("3.2")
+
+      Dir.mktmpdir do |dir|
+        tmpdir = Pathname(dir)
+        script = tmpdir.join("script.rb")
+        script.write <<~EOM
+          describe "things" do
+            it "blerg" do
+            end
+
+            it "flerg"
+            end
+
+            it "zlerg" do
+            end
+          end
+        EOM
+
+        out = `ruby -I#{lib_dir} -rsyntax_suggest #{script} 2>&1`
+
+        expect($?.success?).to be_falsey
+        expect(out).to include('❯  5    it "flerg"').once
+      end
+    end
+
+    it "does not load internals into memory if no syntax error" do
+      Dir.mktmpdir do |dir|
+        tmpdir = Pathname(dir)
+        script = tmpdir.join("script.rb")
+        script.write <<~EOM
+          class Dog
+          end
+
+          if defined?(SyntaxSuggest::DEFAULT_VALUE)
+            puts "SyntaxSuggest is loaded"
+          else
+            puts "SyntaxSuggest is NOT loaded"
+          end
+        EOM
+
+        require_rb = tmpdir.join("require.rb")
+        require_rb.write <<~EOM
+          load "#{script.expand_path}"
+        EOM
+
+        out = `ruby -I#{lib_dir} -rsyntax_suggest #{require_rb} 2>&1`
+
+        expect($?.success?).to be_truthy
+        expect(out).to include("SyntaxSuggest is NOT loaded").once
+      end
+    end
+
+    it "ignores eval" do
+      Dir.mktmpdir do |dir|
+        tmpdir = Pathname(dir)
+        script = tmpdir.join("script.rb")
+        script.write <<~'EOM'
+          $stderr = STDOUT
+          eval("def lol")
+        EOM
+
+        out = `ruby -I#{lib_dir} -rsyntax_suggest #{script} 2>&1`
+
+        expect($?.success?).to be_falsey
+        expect(out).to include("(eval):1")
+
+        expect(out).to_not include("SyntaxSuggest")
+        expect(out).to_not include("Could not find filename")
+      end
+    end
+  end
+end

spec/syntax_suggest/integration/syntax_suggest_spec.rb

@@ -0,0 +1,211 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "Integration tests that don't spawn a process (like using the cli)" do
+    it "does not timeout on massive files" do
+      next unless ENV["SYNTAX_SUGGEST_TIMEOUT"]
+
+      file = fixtures_dir.join("syntax_tree.rb.txt")
+      lines = file.read.lines
+      lines.delete_at(768 - 1)
+
+      io = StringIO.new
+
+      benchmark = Benchmark.measure do
+        debug_perf do
+          SyntaxSuggest.call(
+            io: io,
+            source: lines.join,
+            filename: file
+          )
+        end
+        debug_display(io.string)
+        debug_display(benchmark)
+      end
+
+      expect(io.string).to include(<<~'EOM')
+             6  class SyntaxTree < Ripper
+           170    def self.parse(source)
+           174    end
+        ❯  754    def on_args_add(arguments, argument)
+        ❯  776    class ArgsAddBlock
+        ❯  810    end
+          9233  end
+      EOM
+    end
+
+    it "re-checks all block code, not just what's visible issues/95" do
+      file = fixtures_dir.join("ruby_buildpack.rb.txt")
+      io = StringIO.new
+
+      debug_perf do
+        benchmark = Benchmark.measure do
+          SyntaxSuggest.call(
+            io: io,
+            source: file.read,
+            filename: file
+          )
+        end
+        debug_display(io.string)
+        debug_display(benchmark)
+      end
+
+      expect(io.string).to_not include("def ruby_install_binstub_path")
+      expect(io.string).to include(<<~'EOM')
+        ❯ 1067    def add_yarn_binary
+        ❯ 1068      return [] if yarn_preinstalled?
+        ❯ 1069  |
+        ❯ 1075    end
+      EOM
+    end
+
+    it "returns good results on routes.rb" do
+      source = fixtures_dir.join("routes.rb.txt").read
+
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      debug_display(io.string)
+
+      expect(io.string).to include(<<~'EOM')
+           1  Rails.application.routes.draw do
+        ❯ 113    namespace :admin do
+        ❯ 116    match "/foobar(*path)", via: :all, to: redirect { |_params, req|
+        ❯ 120    }
+          121  end
+      EOM
+    end
+
+    it "handles multi-line-methods issues/64" do
+      source = fixtures_dir.join("webmock.rb.txt").read
+
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      debug_display(io.string)
+
+      expect(io.string).to include(<<~'EOM')
+           1  describe "webmock tests" do
+          22    it "body" do
+          27      query = Cutlass::FunctionQuery.new(
+        ❯ 28        port: port
+        ❯ 29        body: body
+          30      ).call
+          34    end
+          35  end
+      EOM
+    end
+
+    it "handles derailed output issues/50" do
+      source = fixtures_dir.join("derailed_require_tree.rb.txt").read
+
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      debug_display(io.string)
+
+      expect(io.string).to include(<<~'EOM')
+           5  module DerailedBenchmarks
+           6    class RequireTree
+           7      REQUIRED_BY = {}
+           9      attr_reader   :name
+          10      attr_writer   :cost
+        ❯ 13      def initialize(name)
+        ❯ 18      def self.reset!
+        ❯ 25      end
+          73    end
+          74  end
+      EOM
+    end
+
+    it "handles heredocs" do
+      lines = fixtures_dir.join("rexe.rb.txt").read.lines
+      lines.delete_at(85 - 1)
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: lines.join
+      )
+
+      out = io.string
+      debug_display(out)
+
+      expect(out).to include(<<~EOM)
+           16  class Rexe
+        ❯  77    class Lookups
+        ❯  78      def input_modes
+        ❯ 148    end
+          551  end
+      EOM
+    end
+
+    it "rexe" do
+      lines = fixtures_dir.join("rexe.rb.txt").read.lines
+      lines.delete_at(148 - 1)
+      source = lines.join
+
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      out = io.string
+      expect(out).to include(<<~EOM)
+           16  class Rexe
+           18    VERSION = '1.5.1'
+        ❯  77    class Lookups
+        ❯ 140      def format_requires
+        ❯ 148    end
+          551  end
+      EOM
+    end
+
+    it "ambiguous end" do
+      source = <<~'EOM'
+        def call          # 0
+            print "lol"   # 1
+          end # one       # 2
+        end # two         # 3
+      EOM
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      out = io.string
+      expect(out).to include(<<~EOM)
+        ❯ 1  def call          # 0
+        ❯ 3    end # one       # 2
+        ❯ 4  end # two         # 3
+      EOM
+    end
+
+    it "simple regression" do
+      source = <<~'EOM'
+        class Dog
+          def bark
+            puts "woof"
+        end
+      EOM
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      out = io.string
+      expect(out).to include(<<~EOM)
+        ❯ 1  class Dog
+        ❯ 2    def bark
+        ❯ 4  end
+      EOM
+    end
+  end
+end

spec/syntax_suggest/spec_helper.rb

@@ -0,0 +1,90 @@
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "syntax_suggest/api"
+
+require "benchmark"
+require "tempfile"
+
+RSpec.configure do |config|
+  # Enable flags like --only-failures and --next-failure
+  config.example_status_persistence_file_path = ".rspec_status"
+
+  # Disable RSpec exposing methods globally on `Module` and `main`
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end
+
+# Used for debugging modifications to
+# display output
+def debug_display(output)
+  return unless ENV["DEBUG_DISPLAY"]
+  puts
+  puts output
+  puts
+end
+
+def spec_dir
+  Pathname(__dir__)
+end
+
+def lib_dir
+  root_dir.join("lib")
+end
+
+def root_dir
+  spec_dir.join("..")
+end
+
+def fixtures_dir
+  spec_dir.join("fixtures")
+end
+
+def code_line_array(source)
+  SyntaxSuggest::CleanDocument.new(source: source).call.lines
+end
+
+autoload :RubyProf, "ruby-prof"
+
+def debug_perf
+  raise "No block given" unless block_given?
+
+  if ENV["DEBUG_PERF"]
+    out = nil
+    result = RubyProf.profile do
+      out = yield
+    end
+
+    dir = SyntaxSuggest.record_dir("tmp")
+    printer = RubyProf::MultiPrinter.new(result, [:flat, :graph, :graph_html, :tree, :call_tree, :stack, :dot])
+    printer.print(path: dir, profile: "profile")
+
+    out
+  else
+    yield
+  end
+end
+
+def run!(cmd, raise_on_nonzero_exit: true)
+  out = `#{cmd} 2>&1`
+  raise "Command: #{cmd} failed: #{out}" if !$?.success? && raise_on_nonzero_exit
+  out
+end
+
+# Allows us to write cleaner tests since <<~EOM block quotes
+# strip off all leading indentation and we need it to be preserved
+# sometimes.
+class String
+  def indent(number)
+    lines.map do |line|
+      if line.chomp.empty?
+        line
+      else
+        " " * number + line
+      end
+    end.join
+  end
+end

spec/syntax_suggest/unit/api_spec.rb

@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+require "ruby-prof"
+
+module SyntaxSuggest
+  RSpec.describe "Top level SyntaxSuggest api" do
+    it "has a `handle_error` interface" do
+      fake_error = Object.new
+      def fake_error.message
+        "#{__FILE__}:216: unterminated string meets end of file "
+      end
+
+      def fake_error.is_a?(v)
+        true
+      end
+
+      io = StringIO.new
+      SyntaxSuggest.handle_error(
+        fake_error,
+        re_raise: false,
+        io: io
+      )
+
+      expect(io.string.strip).to eq("Syntax OK")
+    end
+
+    it "raises original error with warning if a non-syntax error is passed" do
+      error = NameError.new("blerg")
+      io = StringIO.new
+      expect {
+        SyntaxSuggest.handle_error(
+          error,
+          re_raise: false,
+          io: io
+        )
+      }.to raise_error { |e|
+        expect(io.string).to include("Must pass a SyntaxError")
+        expect(e).to eq(error)
+      }
+    end
+
+    it "raises original error with warning if file is not found" do
+      fake_error = SyntaxError.new
+      def fake_error.message
+        "#does/not/exist/lol/doesnotexist:216: unterminated string meets end of file "
+      end
+
+      io = StringIO.new
+      expect {
+        SyntaxSuggest.handle_error(
+          fake_error,
+          re_raise: false,
+          io: io
+        )
+      }.to raise_error { |e|
+        expect(io.string).to include("Could not find filename")
+        expect(e).to eq(fake_error)
+      }
+    end
+
+    it "respects highlight API" do
+      skip if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("3.2")
+
+      error = SyntaxError.new("#{fixtures_dir.join("this_project_extra_def.rb.txt")}:1 ")
+
+      require "syntax_suggest/core_ext"
+
+      expect(error.detailed_message(highlight: true)).to include(SyntaxSuggest::DisplayCodeWithLineNumbers::TERMINAL_HIGHLIGHT)
+      expect(error.detailed_message(highlight: false)).to_not include(SyntaxSuggest::DisplayCodeWithLineNumbers::TERMINAL_HIGHLIGHT)
+    end
+
+    it "can be disabled via falsey kwarg" do
+      skip if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("3.2")
+
+      error = SyntaxError.new("#{fixtures_dir.join("this_project_extra_def.rb.txt")}:1 ")
+
+      require "syntax_suggest/core_ext"
+
+      expect(error.detailed_message(syntax_suggest: true)).to_not eq(error.detailed_message(syntax_suggest: false))
+    end
+  end
+end

spec/syntax_suggest/unit/around_block_scan_spec.rb

@@ -0,0 +1,165 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe AroundBlockScan do
+    it "continues scan from last location even if scan is false" do
+      source = <<~'EOM'
+        print 'omg'
+        print 'lol'
+        print 'haha'
+      EOM
+      code_lines = CodeLine.from_source(source)
+      block = CodeBlock.new(lines: code_lines[1])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+        .scan_neighbors
+
+      expect(expand.code_block.to_s).to eq(source)
+      expand.scan_while { |line| false }
+
+      expect(expand.code_block.to_s).to eq(source)
+    end
+
+    it "scan_adjacent_indent works on first or last line" do
+      source_string = <<~EOM
+        def foo
+          if [options.output_format_tty, options.output_format_block].include?(nil)
+            raise("Bad output mode '\#{v}'; each must be one of \#{lookups.output_formats.keys}.")
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: code_lines[4])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+        .scan_adjacent_indent
+
+      expect(expand.code_block.to_s).to eq(<<~EOM)
+        def foo
+          if [options.output_format_tty, options.output_format_block].include?(nil)
+            raise("Bad output mode '\#{v}'; each must be one of \#{lookups.output_formats.keys}.")
+          end
+        end
+      EOM
+    end
+
+    it "expands indentation" do
+      source_string = <<~EOM
+        def foo
+          if [options.output_format_tty, options.output_format_block].include?(nil)
+            raise("Bad output mode '\#{v}'; each must be one of \#{lookups.output_formats.keys}.")
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: code_lines[2])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+        .stop_after_kw
+        .scan_adjacent_indent
+
+      expect(expand.code_block.to_s).to eq(<<~EOM.indent(2))
+        if [options.output_format_tty, options.output_format_block].include?(nil)
+          raise("Bad output mode '\#{v}'; each must be one of \#{lookups.output_formats.keys}.")
+        end
+      EOM
+    end
+
+    it "can stop before hitting another end" do
+      source_string = <<~EOM
+        def lol
+        end
+        def foo
+          puts "lol"
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: code_lines[3])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+      expand.stop_after_kw
+      expand.scan_while { true }
+
+      expect(expand.code_block.to_s).to eq(<<~EOM)
+        def foo
+          puts "lol"
+        end
+      EOM
+    end
+
+    it "captures multiple empty and hidden lines" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+
+            puts "lol"
+
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: code_lines[3])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+      expand.scan_while { true }
+
+      expect(expand.before_index).to eq(0)
+      expect(expand.after_index).to eq(6)
+      expect(expand.code_block.to_s).to eq(source_string)
+    end
+
+    it "only takes what you ask" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+
+            puts "lol"
+
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: code_lines[3])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+      expand.scan_while { |line| line.not_empty? }
+
+      expect(expand.code_block.to_s).to eq(<<~EOM.indent(4))
+        puts "lol"
+      EOM
+    end
+
+    it "skips what you want" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+
+            puts "haha"
+            # hide me
+
+            puts "lol"
+
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      code_lines[4].mark_invisible
+
+      block = CodeBlock.new(lines: code_lines[3])
+      expand = AroundBlockScan.new(code_lines: code_lines, block: block)
+      expand.skip(:empty?)
+      expand.skip(:hidden?)
+      expand.scan_neighbors
+
+      expect(expand.code_block.to_s).to eq(<<~EOM.indent(4))
+
+        puts "haha"
+
+        puts "lol"
+
+      EOM
+    end
+  end
+end

spec/syntax_suggest/unit/block_expand_spec.rb

@@ -0,0 +1,200 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe BlockExpand do
+    it "captures multiple empty and hidden lines" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+
+
+            puts "lol"
+
+            # hidden
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+
+      code_lines[6].mark_invisible
+
+      block = CodeBlock.new(lines: [code_lines[3]])
+      expansion = BlockExpand.new(code_lines: code_lines)
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(4))
+
+
+        puts "lol"
+
+      EOM
+    end
+
+    it "captures multiple empty lines" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+
+
+            puts "lol"
+
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: [code_lines[3]])
+      expansion = BlockExpand.new(code_lines: code_lines)
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(4))
+
+
+        puts "lol"
+
+      EOM
+    end
+
+    it "expands neighbors then indentation" do
+      source_string = <<~EOM
+        def foo
+          Foo.call
+            puts "hey"
+            puts "lol"
+            puts "sup"
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: [code_lines[3]])
+      expansion = BlockExpand.new(code_lines: code_lines)
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(4))
+        puts "hey"
+        puts "lol"
+        puts "sup"
+      EOM
+
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(2))
+        Foo.call
+          puts "hey"
+          puts "lol"
+          puts "sup"
+        end
+      EOM
+    end
+
+    it "handles else code" do
+      source_string = <<~EOM
+        Foo.call
+          if blerg
+            puts "lol"
+          else
+            puts "haha"
+          end
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      block = CodeBlock.new(lines: [code_lines[2]])
+      expansion = BlockExpand.new(code_lines: code_lines)
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(2))
+        if blerg
+          puts "lol"
+        else
+          puts "haha"
+        end
+      EOM
+    end
+
+    it "expand until next boundry (indentation)" do
+      source_string = <<~EOM
+        describe "what" do
+          Foo.call
+        end
+
+        describe "hi"
+          Bar.call do
+            Foo.call
+          end
+        end
+
+        it "blerg" do
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+
+      block = CodeBlock.new(
+        lines: code_lines[6]
+      )
+
+      expansion = BlockExpand.new(code_lines: code_lines)
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM.indent(2))
+        Bar.call do
+          Foo.call
+        end
+      EOM
+
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM)
+        describe "hi"
+          Bar.call do
+            Foo.call
+          end
+        end
+      EOM
+    end
+
+    it "expand until next boundry (empty lines)" do
+      source_string = <<~EOM
+        describe "what" do
+        end
+
+        describe "hi"
+        end
+
+        it "blerg" do
+        end
+      EOM
+
+      code_lines = code_line_array(source_string)
+      expansion = BlockExpand.new(code_lines: code_lines)
+
+      block = CodeBlock.new(lines: code_lines[3])
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM)
+
+        describe "hi"
+        end
+
+      EOM
+
+      block = expansion.call(block)
+
+      expect(block.to_s).to eq(<<~EOM)
+        describe "what" do
+        end
+
+        describe "hi"
+        end
+
+        it "blerg" do
+        end
+      EOM
+    end
+  end
+end

spec/syntax_suggest/unit/capture_code_context_spec.rb

@@ -0,0 +1,202 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CaptureCodeContext do
+    it "capture_before_after_kws" do
+      source = <<~'EOM'
+        def sit
+        end
+
+        def bark
+
+        def eat
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      block = CodeBlock.new(lines: code_lines[0])
+
+      display = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+      lines = display.call
+      expect(lines.join).to eq(<<~'EOM')
+        def sit
+        end
+        def bark
+        def eat
+        end
+      EOM
+    end
+
+    it "handles ambiguous end" do
+      source = <<~'EOM'
+        def call          # 0
+            print "lol"   # 1
+          end # one       # 2
+        end # two         # 3
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      code_lines[0..2].each(&:mark_invisible)
+      block = CodeBlock.new(lines: code_lines)
+
+      display = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+      lines = display.call
+
+      lines = lines.sort.map(&:original)
+
+      expect(lines.join).to eq(<<~'EOM')
+        def call          # 0
+          end # one       # 2
+        end # two         # 3
+      EOM
+    end
+
+    it "shows ends of captured block" do
+      lines = fixtures_dir.join("rexe.rb.txt").read.lines
+      lines.delete_at(148 - 1)
+      source = lines.join
+
+      code_lines = CleanDocument.new(source: source).call.lines
+
+      code_lines[0..75].each(&:mark_invisible)
+      code_lines[77..-1].each(&:mark_invisible)
+      expect(code_lines.join.strip).to eq("class Lookups")
+
+      block = CodeBlock.new(lines: code_lines[76..149])
+
+      display = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+      lines = display.call
+
+      lines = lines.sort.map(&:original)
+      expect(lines.join).to include(<<~'EOM'.indent(2))
+        class Lookups
+          def format_requires
+        end
+      EOM
+    end
+
+    it "shows ends of captured block" do
+      source = <<~'EOM'
+        class Dog
+          def bark
+            puts "woof"
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      block = CodeBlock.new(lines: code_lines)
+      code_lines[1..-1].each(&:mark_invisible)
+
+      expect(block.to_s.strip).to eq("class Dog")
+
+      display = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+      lines = display.call.sort.map(&:original)
+      expect(lines.join).to eq(<<~'EOM')
+        class Dog
+          def bark
+        end
+      EOM
+    end
+
+    it "captures surrounding context on falling indent" do
+      source = <<~'EOM'
+        class Blerg
+        end
+
+        class OH
+
+          def hello
+            it "foo" do
+          end
+        end
+
+        class Zerg
+        end
+      EOM
+      code_lines = CleanDocument.new(source: source).call.lines
+      block = CodeBlock.new(lines: code_lines[6])
+
+      expect(block.to_s.strip).to eq('it "foo" do')
+
+      display = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+      lines = display.call.sort.map(&:original)
+      expect(lines.join).to eq(<<~'EOM')
+        class OH
+          def hello
+            it "foo" do
+          end
+        end
+      EOM
+    end
+
+    it "captures surrounding context on same indent" do
+      source = <<~'EOM'
+        class Blerg
+        end
+        class OH
+
+          def nope
+          end
+
+          def lol
+          end
+
+          end # here
+
+          def haha
+          end
+
+          def nope
+          end
+        end
+
+        class Zerg
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      block = CodeBlock.new(lines: code_lines[7..10])
+      expect(block.to_s).to eq(<<~'EOM'.indent(2))
+        def lol
+        end
+
+        end # here
+      EOM
+
+      code_context = CaptureCodeContext.new(
+        blocks: [block],
+        code_lines: code_lines
+      )
+
+      lines = code_context.call
+      out = DisplayCodeWithLineNumbers.new(
+        lines: lines
+      ).call
+
+      expect(out).to eq(<<~'EOM'.indent(2))
+         3  class OH
+         8    def lol
+         9    end
+        11    end # here
+        18  end
+      EOM
+    end
+  end
+end

spec/syntax_suggest/unit/clean_document_spec.rb

@@ -0,0 +1,259 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CleanDocument do
+    it "heredocs" do
+      source = fixtures_dir.join("this_project_extra_def.rb.txt").read
+      code_lines = CleanDocument.new(source: source).call.lines
+
+      expect(code_lines[18 - 1].to_s).to eq(<<-'EOL')
+      @io.puts <<~EOM
+
+        SyntaxSuggest: A syntax error was detected
+
+        This code has an unmatched `end` this is caused by either
+        missing a syntax keyword (`def`,  `do`, etc.) or inclusion
+        of an extra `end` line:
+      EOM
+      EOL
+      expect(code_lines[18].to_s).to eq("")
+
+      expect(code_lines[27 - 1].to_s).to eq(<<-'EOL')
+      @io.puts(<<~EOM) if filename
+        file: #{filename}
+      EOM
+      EOL
+      expect(code_lines[27].to_s).to eq("")
+
+      expect(code_lines[31 - 1].to_s).to eq(<<-'EOL')
+      @io.puts <<~EOM
+        #{code_with_filename}
+      EOM
+      EOL
+      expect(code_lines[31].to_s).to eq("")
+    end
+
+    it "joins: multi line methods" do
+      source = <<~EOM
+        User
+          .where(name: 'schneems')
+          .first
+      EOM
+
+      doc = CleanDocument.new(source: source).join_consecutive!
+
+      expect(doc.lines[0].to_s).to eq(source)
+      expect(doc.lines[1].to_s).to eq("")
+      expect(doc.lines[2].to_s).to eq("")
+      expect(doc.lines[3]).to eq(nil)
+
+      lines = doc.lines
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: lines
+        ).call
+      ).to eq(<<~'EOM'.indent(2))
+        1  User
+        2    .where(name: 'schneems')
+        3    .first
+      EOM
+
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: lines,
+          highlight_lines: lines[0]
+        ).call
+      ).to eq(<<~'EOM')
+        ❯ 1  User
+        ❯ 2    .where(name: 'schneems')
+        ❯ 3    .first
+      EOM
+    end
+
+    it "helper method: take_while_including" do
+      source = <<~EOM
+        User
+          .where(name: 'schneems')
+          .first
+      EOM
+
+      doc = CleanDocument.new(source: source)
+
+      lines = doc.take_while_including { |line| !line.to_s.include?("where") }
+      expect(lines.count).to eq(2)
+    end
+
+    it "comments: removes comments" do
+      source = <<~EOM
+        # lol
+        puts "what"
+          # yolo
+      EOM
+
+      out = CleanDocument.new(source: source).lines.join
+      expect(out.to_s).to eq(<<~EOM)
+
+        puts "what"
+
+      EOM
+    end
+
+    it "whitespace: removes whitespace" do
+      source = "  \n" + <<~EOM
+        puts "what"
+      EOM
+
+      out = CleanDocument.new(source: source).lines.join
+      expect(out.to_s).to eq(<<~EOM)
+
+        puts "what"
+      EOM
+
+      expect(source.lines.first.to_s).to_not eq("\n")
+      expect(out.lines.first.to_s).to eq("\n")
+    end
+
+    it "trailing slash: does not join trailing do" do
+      # Some keywords and syntaxes trigger the "ignored line"
+      # lex output, we ignore them by filtering by BEG
+      #
+      # The `do` keyword is one of these:
+      # https://gist.github.com/schneems/6a7d7f988d3329fb3bd4b5be3e2efc0c
+      source = <<~EOM
+        foo do
+          puts "lol"
+        end
+      EOM
+
+      doc = CleanDocument.new(source: source).join_consecutive!
+
+      expect(doc.lines[0].to_s).to eq(source.lines[0])
+      expect(doc.lines[1].to_s).to eq(source.lines[1])
+      expect(doc.lines[2].to_s).to eq(source.lines[2])
+    end
+
+    it "trailing slash: formats output" do
+      source = <<~'EOM'
+        context "timezones workaround" do
+          it "should receive a time in UTC format and return the time with the"\
+            "office's UTC offset substracted from it" do
+            travel_to DateTime.new(2020, 10, 1, 10, 0, 0) do
+              office = build(:office)
+            end
+          end
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: code_lines.select(&:visible?)
+        ).call
+      ).to eq(<<~'EOM'.indent(2))
+        1  context "timezones workaround" do
+        2    it "should receive a time in UTC format and return the time with the"\
+        3      "office's UTC offset substracted from it" do
+        4      travel_to DateTime.new(2020, 10, 1, 10, 0, 0) do
+        5        office = build(:office)
+        6      end
+        7    end
+        8  end
+      EOM
+
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: code_lines.select(&:visible?),
+          highlight_lines: code_lines[1]
+        ).call
+      ).to eq(<<~'EOM')
+          1  context "timezones workaround" do
+        ❯ 2    it "should receive a time in UTC format and return the time with the"\
+        ❯ 3      "office's UTC offset substracted from it" do
+          4      travel_to DateTime.new(2020, 10, 1, 10, 0, 0) do
+          5        office = build(:office)
+          6      end
+          7    end
+          8  end
+      EOM
+    end
+
+    it "trailing slash: basic detection" do
+      source = <<~'EOM'
+        it "trailing s" \
+           "lash" do
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+
+      expect(code_lines[0]).to_not be_hidden
+      expect(code_lines[1]).to be_hidden
+
+      expect(
+        code_lines.join
+      ).to eq(code_lines.map(&:original).join)
+    end
+
+    it "trailing slash: joins multiple lines" do
+      source = <<~'EOM'
+        it "should " \
+           "keep " \
+           "going " do
+        end
+      EOM
+
+      doc = CleanDocument.new(source: source).join_trailing_slash!
+      expect(doc.lines[0].to_s).to eq(source.lines[0..2].join)
+      expect(doc.lines[1].to_s).to eq("")
+      expect(doc.lines[2].to_s).to eq("")
+      expect(doc.lines[3].to_s).to eq(source.lines[3])
+
+      lines = doc.lines
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: lines
+        ).call
+      ).to eq(<<~'EOM'.indent(2))
+        1  it "should " \
+        2     "keep " \
+        3     "going " do
+        4  end
+      EOM
+
+      expect(
+        DisplayCodeWithLineNumbers.new(
+          lines: lines,
+          highlight_lines: lines[0]
+        ).call
+      ).to eq(<<~'EOM')
+        ❯ 1  it "should " \
+        ❯ 2     "keep " \
+        ❯ 3     "going " do
+          4  end
+      EOM
+    end
+
+    it "trailing slash: no false positives" do
+      source = <<~'EOM'
+        def formatters
+          @formatters ||=  {
+              amazing_print: ->(obj)  { obj.ai + "\n" },
+              inspect:       ->(obj)  { obj.inspect + "\n" },
+              json:          ->(obj)  { obj.to_json },
+              marshal:       ->(obj)  { Marshal.dump(obj) },
+              none:          ->(_obj) { nil },
+              pretty_json:   ->(obj)  { JSON.pretty_generate(obj) },
+              pretty_print:  ->(obj)  { obj.pretty_inspect },
+              puts:          ->(obj)  { require 'stringio'; sio = StringIO.new; sio.puts(obj); sio.string },
+              to_s:          ->(obj)  { obj.to_s + "\n" },
+              yaml:          ->(obj)  { obj.to_yaml },
+          }
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      expect(code_lines.join).to eq(code_lines.join)
+    end
+  end
+end

spec/syntax_suggest/unit/cli_spec.rb

@@ -0,0 +1,224 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  class FakeExit
+    def initialize
+      @called = false
+      @value = nil
+    end
+
+    def exit(value = nil)
+      @called = true
+      @value = value
+    end
+
+    def called?
+      @called
+    end
+
+    attr_reader :value
+  end
+
+  RSpec.describe Cli do
+    it "parses valid code" do
+      Dir.mktmpdir do |dir|
+        dir = Pathname(dir)
+        file = dir.join("script.rb")
+        file.write("puts 'lol'")
+
+        io = StringIO.new
+        exit_obj = FakeExit.new
+        Cli.new(
+          io: io,
+          argv: [file.to_s],
+          exit_obj: exit_obj
+        ).call
+
+        expect(exit_obj.called?).to be_truthy
+        expect(exit_obj.value).to eq(0)
+        expect(io.string.strip).to eq("Syntax OK")
+      end
+    end
+
+    it "parses invalid code" do
+      file = fixtures_dir.join("this_project_extra_def.rb.txt")
+
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      Cli.new(
+        io: io,
+        argv: [file.to_s],
+        exit_obj: exit_obj
+      ).call
+
+      out = io.string
+      debug_display(out)
+
+      expect(exit_obj.called?).to be_truthy
+      expect(exit_obj.value).to eq(1)
+      expect(out.strip).to include("❯ 36      def filename")
+    end
+
+    it "parses valid code with flags" do
+      Dir.mktmpdir do |dir|
+        dir = Pathname(dir)
+        file = dir.join("script.rb")
+        file.write("puts 'lol'")
+
+        io = StringIO.new
+        exit_obj = FakeExit.new
+        cli = Cli.new(
+          io: io,
+          argv: ["--terminal", file.to_s],
+          exit_obj: exit_obj
+        )
+        cli.call
+
+        expect(exit_obj.called?).to be_truthy
+        expect(exit_obj.value).to eq(0)
+        expect(cli.options[:terminal]).to be_truthy
+        expect(io.string.strip).to eq("Syntax OK")
+      end
+    end
+
+    it "errors when no file given" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: ["--terminal"],
+        exit_obj: exit_obj
+      )
+      cli.call
+
+      expect(exit_obj.called?).to be_truthy
+      expect(exit_obj.value).to eq(1)
+      expect(io.string.strip).to eq("No file given")
+    end
+
+    it "errors when file does not exist" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: ["lol-i-d-o-not-ex-ist-yololo.txtblerglol"],
+        exit_obj: exit_obj
+      )
+      cli.call
+
+      expect(exit_obj.called?).to be_truthy
+      expect(exit_obj.value).to eq(1)
+      expect(io.string.strip).to include("file not found:")
+    end
+
+    # We cannot execute the parser here
+    # because it calls `exit` and it will exit
+    # our tests, however we can assert that the
+    # parser has the right value for version
+    it "-v version" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      parser = Cli.new(
+        io: io,
+        argv: ["-v"],
+        exit_obj: exit_obj
+      ).parser
+
+      expect(parser.version).to include(SyntaxSuggest::VERSION.to_s)
+    end
+
+    it "SYNTAX_SUGGEST_RECORD_DIR" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: [],
+        env: {"SYNTAX_SUGGEST_RECORD_DIR" => "hahaha"},
+        exit_obj: exit_obj
+      ).parse
+
+      expect(exit_obj.called?).to be_falsey
+      expect(cli.options[:record_dir]).to eq("hahaha")
+    end
+
+    it "--record-dir=<dir>" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: ["--record=lol"],
+        exit_obj: exit_obj
+      ).parse
+
+      expect(exit_obj.called?).to be_falsey
+      expect(cli.options[:record_dir]).to eq("lol")
+    end
+
+    it "terminal default to respecting TTY" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: [],
+        exit_obj: exit_obj
+      ).parse
+
+      expect(exit_obj.called?).to be_falsey
+      expect(cli.options[:terminal]).to eq(SyntaxSuggest::DEFAULT_VALUE)
+    end
+
+    it "--terminal" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: ["--terminal"],
+        exit_obj: exit_obj
+      ).parse
+
+      expect(exit_obj.called?).to be_falsey
+      expect(cli.options[:terminal]).to be_truthy
+    end
+
+    it "--no-terminal" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      cli = Cli.new(
+        io: io,
+        argv: ["--no-terminal"],
+        exit_obj: exit_obj
+      ).parse
+
+      expect(exit_obj.called?).to be_falsey
+      expect(cli.options[:terminal]).to be_falsey
+    end
+
+    it "--help outputs help" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      Cli.new(
+        io: io,
+        argv: ["--help"],
+        exit_obj: exit_obj
+      ).call
+
+      expect(exit_obj.called?).to be_truthy
+      expect(io.string).to include("Usage: syntax_suggest <file> [options]")
+    end
+
+    it "<empty args> outputs help" do
+      io = StringIO.new
+      exit_obj = FakeExit.new
+      Cli.new(
+        io: io,
+        argv: [],
+        exit_obj: exit_obj
+      ).call
+
+      expect(exit_obj.called?).to be_truthy
+      expect(io.string).to include("Usage: syntax_suggest <file> [options]")
+    end
+  end
+end

spec/syntax_suggest/unit/code_block_spec.rb

@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CodeBlock do
+    it "can detect if it's valid or not" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts 'lol'
+        end
+      EOM
+
+      block = CodeBlock.new(lines: code_lines[1])
+      expect(block.valid?).to be_truthy
+    end
+
+    it "can be sorted in indentation order" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts 'lol'
+            end
+      EOM
+
+      block_0 = CodeBlock.new(lines: code_lines[0])
+      block_1 = CodeBlock.new(lines: code_lines[1])
+      block_2 = CodeBlock.new(lines: code_lines[2])
+
+      expect(block_0 <=> block_0.dup).to eq(0)
+      expect(block_1 <=> block_0).to eq(1)
+      expect(block_1 <=> block_2).to eq(-1)
+
+      array = [block_2, block_1, block_0].sort
+      expect(array.last).to eq(block_2)
+
+      block = CodeBlock.new(lines: CodeLine.new(line: " " * 8 + "foo", index: 4, lex: []))
+      array.prepend(block)
+      expect(array.max).to eq(block)
+    end
+
+    it "knows it's current indentation level" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts 'lol'
+        end
+      EOM
+
+      block = CodeBlock.new(lines: code_lines[1])
+      expect(block.current_indent).to eq(2)
+
+      block = CodeBlock.new(lines: code_lines[0])
+      expect(block.current_indent).to eq(0)
+    end
+
+    it "knows it's current indentation level when mismatched indents" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts 'lol'
+         end
+      EOM
+
+      block = CodeBlock.new(lines: [code_lines[1], code_lines[2]])
+      expect(block.current_indent).to eq(1)
+    end
+
+    it "before lines and after lines" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          bar; end
+        end
+      EOM
+
+      block = CodeBlock.new(lines: code_lines[1])
+      expect(block.valid?).to be_falsey
+    end
+  end
+end

spec/syntax_suggest/unit/code_frontier_spec.rb

@@ -0,0 +1,135 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CodeFrontier do
+    it "detect_bad_blocks" do
+      code_lines = code_line_array(<<~EOM)
+        describe "lol" do
+          end
+        end
+
+        it "lol" do
+          end
+        end
+      EOM
+
+      frontier = CodeFrontier.new(code_lines: code_lines)
+      blocks = []
+      blocks << CodeBlock.new(lines: code_lines[1])
+      blocks << CodeBlock.new(lines: code_lines[5])
+      blocks.each do |b|
+        frontier << b
+      end
+
+      expect(frontier.detect_invalid_blocks.sort).to eq(blocks.sort)
+    end
+
+    it "self.combination" do
+      expect(
+        CodeFrontier.combination([:a, :b, :c, :d])
+      ).to eq(
+        [
+          [:a], [:b], [:c], [:d],
+          [:a, :b],
+          [:a, :c],
+          [:a, :d],
+          [:b, :c],
+          [:b, :d],
+          [:c, :d],
+          [:a, :b, :c],
+          [:a, :b, :d],
+          [:a, :c, :d],
+          [:b, :c, :d],
+          [:a, :b, :c, :d]
+        ]
+      )
+    end
+
+    it "doesn't duplicate blocks" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts "lol"
+          puts "lol"
+          puts "lol"
+        end
+      EOM
+
+      frontier = CodeFrontier.new(code_lines: code_lines)
+      frontier << CodeBlock.new(lines: [code_lines[2]])
+      expect(frontier.count).to eq(1)
+
+      frontier << CodeBlock.new(lines: [code_lines[1], code_lines[2], code_lines[3]])
+      # expect(frontier.count).to eq(1)
+      expect(frontier.pop.to_s).to eq(<<~EOM.indent(2))
+        puts "lol"
+        puts "lol"
+        puts "lol"
+      EOM
+
+      expect(frontier.pop).to be_nil
+
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts "lol"
+          puts "lol"
+          puts "lol"
+        end
+      EOM
+
+      frontier = CodeFrontier.new(code_lines: code_lines)
+      frontier << CodeBlock.new(lines: [code_lines[2]])
+      expect(frontier.count).to eq(1)
+
+      frontier << CodeBlock.new(lines: [code_lines[3]])
+      expect(frontier.count).to eq(2)
+      expect(frontier.pop.to_s).to eq(<<~EOM.indent(2))
+        puts "lol"
+      EOM
+    end
+
+    it "detects if multiple syntax errors are found" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          end
+        end
+      EOM
+
+      frontier = CodeFrontier.new(code_lines: code_lines)
+
+      frontier << CodeBlock.new(lines: code_lines[1])
+      block = frontier.pop
+      expect(block.to_s).to eq(<<~EOM.indent(2))
+        end
+      EOM
+      frontier << block
+
+      expect(frontier.holds_all_syntax_errors?).to be_truthy
+    end
+
+    it "detects if it has not captured all syntax errors" do
+      code_lines = code_line_array(<<~EOM)
+        def foo
+          puts "lol"
+        end
+
+        describe "lol"
+        end
+
+        it "lol"
+        end
+      EOM
+
+      frontier = CodeFrontier.new(code_lines: code_lines)
+      frontier << CodeBlock.new(lines: [code_lines[1]])
+      block = frontier.pop
+      expect(block.to_s).to eq(<<~EOM.indent(2))
+        puts "lol"
+      EOM
+      frontier << block
+
+      expect(frontier.holds_all_syntax_errors?).to be_falsey
+    end
+  end
+end

spec/syntax_suggest/unit/code_line_spec.rb

@@ -0,0 +1,164 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CodeLine do
+    it "bug in keyword detection" do
+      lines = CodeLine.from_source(<<~'EOM')
+        def to_json(*opts)
+          {
+            type: :module,
+          }.to_json(*opts)
+        end
+      EOM
+      expect(lines.count(&:is_kw?)).to eq(1)
+      expect(lines.count(&:is_end?)).to eq(1)
+    end
+
+    it "supports endless method definitions" do
+      skip("Unsupported ruby version") unless Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3")
+
+      line = CodeLine.from_source(<<~'EOM').first
+        def square(x) = x * x
+      EOM
+
+      expect(line.is_kw?).to be_falsey
+      expect(line.is_end?).to be_falsey
+    end
+
+    it "retains original line value, after being marked invisible" do
+      line = CodeLine.from_source(<<~'EOM').first
+        puts "lol"
+      EOM
+      expect(line.line).to match('puts "lol"')
+      line.mark_invisible
+      expect(line.line).to eq("")
+      expect(line.original).to match('puts "lol"')
+    end
+
+    it "knows which lines can be joined" do
+      code_lines = CodeLine.from_source(<<~'EOM')
+        user = User.
+          where(name: 'schneems').
+          first
+        puts user.name
+      EOM
+
+      # Indicates line 1 can join 2, 2 can join 3, but 3 won't join it's next line
+      expect(code_lines.map(&:ignore_newline_not_beg?)).to eq([true, true, false, false])
+    end
+    it "trailing if" do
+      code_lines = CodeLine.from_source(<<~'EOM')
+        puts "lol" if foo
+        if foo
+        end
+      EOM
+
+      expect(code_lines.map(&:is_kw?)).to eq([false, true, false])
+    end
+
+    it "trailing unless" do
+      code_lines = CodeLine.from_source(<<~'EOM')
+        puts "lol" unless foo
+        unless foo
+        end
+      EOM
+
+      expect(code_lines.map(&:is_kw?)).to eq([false, true, false])
+    end
+
+    it "trailing slash" do
+      code_lines = CodeLine.from_source(<<~'EOM')
+        it "trailing s" \
+           "lash" do
+      EOM
+
+      expect(code_lines.map(&:trailing_slash?)).to eq([true, false])
+
+      code_lines = CodeLine.from_source(<<~'EOM')
+        amazing_print: ->(obj)  { obj.ai + "\n" },
+      EOM
+      expect(code_lines.map(&:trailing_slash?)).to eq([false])
+    end
+
+    it "knows it's got an end" do
+      line = CodeLine.from_source("   end").first
+
+      expect(line.is_end?).to be_truthy
+      expect(line.is_kw?).to be_falsey
+    end
+
+    it "knows it's got a keyword" do
+      line = CodeLine.from_source("  if").first
+
+      expect(line.is_end?).to be_falsey
+      expect(line.is_kw?).to be_truthy
+    end
+
+    it "ignores marked lines" do
+      code_lines = CodeLine.from_source(<<~EOM)
+        def foo
+          Array(value) |x|
+          end
+        end
+      EOM
+
+      expect(SyntaxSuggest.valid?(code_lines)).to be_falsey
+      expect(code_lines.join).to eq(<<~EOM)
+        def foo
+          Array(value) |x|
+          end
+        end
+      EOM
+
+      expect(code_lines[0].visible?).to be_truthy
+      expect(code_lines[3].visible?).to be_truthy
+
+      code_lines[0].mark_invisible
+      code_lines[3].mark_invisible
+
+      expect(code_lines[0].visible?).to be_falsey
+      expect(code_lines[3].visible?).to be_falsey
+
+      expect(code_lines.join).to eq(<<~EOM.indent(2))
+        Array(value) |x|
+        end
+      EOM
+      expect(SyntaxSuggest.valid?(code_lines)).to be_falsey
+    end
+
+    it "knows empty lines" do
+      code_lines = CodeLine.from_source(<<~EOM)
+        # Not empty
+
+        # Not empty
+      EOM
+
+      expect(code_lines.map(&:empty?)).to eq([false, true, false])
+      expect(code_lines.map(&:not_empty?)).to eq([true, false, true])
+      expect(code_lines.map { |l| SyntaxSuggest.valid?(l) }).to eq([true, true, true])
+    end
+
+    it "counts indentations" do
+      code_lines = CodeLine.from_source(<<~EOM)
+        def foo
+          Array(value) |x|
+            puts 'lol'
+          end
+        end
+      EOM
+
+      expect(code_lines.map(&:indent)).to eq([0, 2, 4, 2, 0])
+    end
+
+    it "doesn't count empty lines as having an indentation" do
+      code_lines = CodeLine.from_source(<<~EOM)
+
+
+      EOM
+
+      expect(code_lines.map(&:indent)).to eq([0, 0])
+    end
+  end
+end

spec/syntax_suggest/unit/code_search_spec.rb

@@ -0,0 +1,505 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe CodeSearch do
+    it "rexe regression" do
+      lines = fixtures_dir.join("rexe.rb.txt").read.lines
+      lines.delete_at(148 - 1)
+      source = lines.join
+
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join.strip).to eq(<<~'EOM'.strip)
+        class Lookups
+      EOM
+    end
+
+    it "squished do regression" do
+      source = <<~'EOM'
+        def call
+          trydo
+
+            @options = CommandLineParser.new.parse
+
+            options.requires.each { |r| require!(r) }
+            load_global_config_if_exists
+            options.loads.each { |file| load(file) }
+
+            @user_source_code = ARGV.join(' ')
+            @user_source_code = 'self' if @user_source_code == ''
+
+            @callable = create_callable
+
+            init_rexe_context
+            init_parser_and_formatters
+
+            # This is where the user's source code will be executed; the action will in turn call `execute`.
+            lookup_action(options.input_mode).call unless options.noop
+
+            output_log_entry
+          end # one
+        end # two
+      EOM
+
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        trydo
+        end # one
+      EOM
+    end
+
+    it "regression test ambiguous end" do
+      source = <<~'EOM'
+        def call          # 0
+            print "lol"   # 1
+          end # one       # 2
+        end # two         # 3
+      EOM
+
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM')
+        end # two         # 3
+      EOM
+    end
+
+    it "regression dog test" do
+      source = <<~'EOM'
+        class Dog
+          def bark
+            puts "woof"
+        end
+      EOM
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM')
+        class Dog
+      EOM
+      expect(search.invalid_blocks.first.lines.length).to eq(4)
+    end
+
+    it "handles mismatched |" do
+      source = <<~EOM
+        class Blerg
+          Foo.call do |a
+          end # one
+
+          puts lol
+          class Foo
+          end # two
+        end # three
+      EOM
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        Foo.call do |a
+        end # one
+      EOM
+    end
+
+    it "handles mismatched }" do
+      source = <<~EOM
+        class Blerg
+          Foo.call do {
+
+          puts lol
+          class Foo
+          end # two
+        end # three
+      EOM
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        Foo.call do {
+      EOM
+    end
+
+    it "handles no spaces between blocks and trailing slash" do
+      source = <<~'EOM'
+        require "rails_helper"
+        RSpec.describe Foo, type: :model do
+          describe "#bar" do
+            context "context" do
+              it "foos the bar with a foo and then bazes the foo with a bar to"\
+                "fooify the barred bar" do
+                travel_to DateTime.new(2020, 10, 1, 10, 0, 0) do
+                  foo = build(:foo)
+                end
+              end
+            end
+          end
+          describe "#baz?" do
+            context "baz has barred the foo" do
+              it "returns true" do # <== HERE
+            end
+          end
+        end
+      EOM
+
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join.strip).to eq('it "returns true" do # <== HERE')
+    end
+
+    it "handles no spaces between blocks" do
+      source = <<~'EOM'
+        context "foo bar" do
+          it "bars the foo" do
+            travel_to DateTime.new(2020, 10, 1, 10, 0, 0) do
+            end
+          end
+        end
+        context "test" do
+          it "should" do
+        end
+      EOM
+      search = CodeSearch.new(source)
+      search.call
+
+      expect(search.invalid_blocks.join.strip).to eq('it "should" do')
+    end
+
+    it "records debugging steps to a directory" do
+      Dir.mktmpdir do |dir|
+        dir = Pathname(dir)
+        search = CodeSearch.new(<<~'EOM', record_dir: dir)
+          class OH
+            def hello
+            def hai
+            end
+          end
+        EOM
+        search.call
+
+        expect(search.record_dir.entries.map(&:to_s)).to include("1-add-1-(3__4).txt")
+        expect(search.record_dir.join("1-add-1-(3__4).txt").read).to include(<<~EOM)
+            1  class OH
+            2    def hello
+          ❯ 3    def hai
+          ❯ 4    end
+            5  end
+        EOM
+      end
+    end
+
+    it "def with missing end" do
+      search = CodeSearch.new(<<~'EOM')
+        class OH
+          def hello
+
+          def hai
+            puts "lol"
+          end
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join.strip).to eq("def hello")
+
+      search = CodeSearch.new(<<~'EOM')
+        class OH
+          def hello
+
+          def hai
+          end
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join.strip).to eq("def hello")
+
+      search = CodeSearch.new(<<~'EOM')
+        class OH
+          def hello
+          def hai
+          end
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        def hello
+      EOM
+    end
+
+    describe "real world cases" do
+      it "finds hanging def in this project" do
+        source_string = fixtures_dir.join("this_project_extra_def.rb.txt").read
+        search = CodeSearch.new(source_string)
+        search.call
+
+        document = DisplayCodeWithLineNumbers.new(
+          lines: search.code_lines.select(&:visible?),
+          terminal: false,
+          highlight_lines: search.invalid_blocks.flat_map(&:lines)
+        ).call
+
+        expect(document).to include(<<~'EOM')
+          ❯ 36      def filename
+        EOM
+      end
+
+      it "Format Code blocks real world example" do
+        search = CodeSearch.new(<<~'EOM')
+          require 'rails_helper'
+
+          RSpec.describe AclassNameHere, type: :worker do
+            describe "thing" do
+              context "when" do
+                let(:thing) { stuff }
+                let(:another_thing) { moarstuff }
+                subject { foo.new.perform(foo.id, true) }
+
+                it "stuff" do
+                  subject
+
+                  expect(foo.foo.foo).to eq(true)
+                end
+              end
+            end # line 16 accidental end, but valid block
+
+              context "stuff" do
+                let(:thing) { create(:foo, foo: stuff) }
+                let(:another_thing) { create(:stuff) }
+
+                subject { described_class.new.perform(foo.id, false) }
+
+                it "more stuff" do
+                  subject
+
+                  expect(foo.foo.foo).to eq(false)
+                end
+              end
+            end # mismatched due to 16
+          end
+        EOM
+        search.call
+
+        document = DisplayCodeWithLineNumbers.new(
+          lines: search.code_lines.select(&:visible?),
+          terminal: false,
+          highlight_lines: search.invalid_blocks.flat_map(&:lines)
+        ).call
+
+        expect(document).to include(<<~'EOM')
+             1  require 'rails_helper'
+             2
+             3  RSpec.describe AclassNameHere, type: :worker do
+          ❯  4    describe "thing" do
+          ❯ 16    end # line 16 accidental end, but valid block
+          ❯ 30    end # mismatched due to 16
+            31  end
+        EOM
+      end
+    end
+
+    # For code that's not perfectly formatted, we ideally want to do our best
+    # These examples represent the results that exist today, but I would like to improve upon them
+    describe "needs improvement" do
+      describe "mis-matched-indentation" do
+        it "extra space before end" do
+          search = CodeSearch.new(<<~'EOM')
+            Foo.call
+              def foo
+                puts "lol"
+                puts "lol"
+               end # one
+            end # two
+          EOM
+          search.call
+
+          expect(search.invalid_blocks.join).to eq(<<~'EOM')
+            Foo.call
+            end # two
+          EOM
+        end
+
+        it "stacked ends 2" do
+          search = CodeSearch.new(<<~'EOM')
+            def cat
+              blerg
+            end
+
+            Foo.call do
+            end # one
+            end # two
+
+            def dog
+            end
+          EOM
+          search.call
+
+          expect(search.invalid_blocks.join).to eq(<<~'EOM')
+            Foo.call do
+            end # one
+            end # two
+
+          EOM
+        end
+
+        it "stacked ends " do
+          search = CodeSearch.new(<<~'EOM')
+            Foo.call
+              def foo
+                puts "lol"
+                puts "lol"
+            end
+            end
+          EOM
+          search.call
+
+          expect(search.invalid_blocks.join).to eq(<<~'EOM')
+            Foo.call
+            end
+          EOM
+        end
+
+        it "missing space before end" do
+          search = CodeSearch.new(<<~'EOM')
+            Foo.call
+
+              def foo
+                puts "lol"
+                puts "lol"
+             end
+            end
+          EOM
+          search.call
+
+          # expand-1 and expand-2 seem to be broken?
+          expect(search.invalid_blocks.join).to eq(<<~'EOM')
+            Foo.call
+            end
+          EOM
+        end
+      end
+    end
+
+    it "returns syntax error in outer block without inner block" do
+      search = CodeSearch.new(<<~'EOM')
+        Foo.call
+          def foo
+            puts "lol"
+            puts "lol"
+          end # one
+        end # two
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM')
+        Foo.call
+        end # two
+      EOM
+    end
+
+    it "doesn't just return an empty `end`" do
+      search = CodeSearch.new(<<~'EOM')
+        Foo.call
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM')
+        Foo.call
+        end
+      EOM
+    end
+
+    it "finds multiple syntax errors" do
+      search = CodeSearch.new(<<~'EOM')
+        describe "hi" do
+          Foo.call
+          end
+        end
+
+        it "blerg" do
+          Bar.call
+          end
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        Foo.call
+        end
+        Bar.call
+        end
+      EOM
+    end
+
+    it "finds a typo def" do
+      search = CodeSearch.new(<<~'EOM')
+        defzfoo
+          puts "lol"
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM')
+        defzfoo
+        end
+      EOM
+    end
+
+    it "finds a mis-matched def" do
+      search = CodeSearch.new(<<~'EOM')
+        def foo
+          def blerg
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        def blerg
+      EOM
+    end
+
+    it "finds a naked end" do
+      search = CodeSearch.new(<<~'EOM')
+        def foo
+          end # one
+        end # two
+      EOM
+      search.call
+
+      expect(search.invalid_blocks.join).to eq(<<~'EOM'.indent(2))
+        end # one
+      EOM
+    end
+
+    it "returns when no invalid blocks are found" do
+      search = CodeSearch.new(<<~'EOM')
+        def foo
+          puts 'lol'
+        end
+      EOM
+      search.call
+
+      expect(search.invalid_blocks).to eq([])
+    end
+
+    it "expands frontier by eliminating valid lines" do
+      search = CodeSearch.new(<<~'EOM')
+        def foo
+          puts 'lol'
+        end
+      EOM
+      search.create_blocks_from_untracked_lines
+
+      expect(search.code_lines.join).to eq(<<~'EOM')
+        def foo
+        end
+      EOM
+    end
+  end
+end

spec/syntax_suggest/unit/display_invalid_blocks_spec.rb

@@ -0,0 +1,172 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe DisplayInvalidBlocks do
+    it "works with valid code" do
+      syntax_string = <<~EOM
+        class OH
+          def hello
+          end
+          def hai
+          end
+        end
+      EOM
+
+      search = CodeSearch.new(syntax_string)
+      search.call
+
+      io = StringIO.new
+      display = DisplayInvalidBlocks.new(
+        io: io,
+        blocks: search.invalid_blocks,
+        terminal: false,
+        code_lines: search.code_lines
+      )
+      display.call
+      expect(io.string).to include("Syntax OK")
+    end
+
+    it "selectively prints to terminal if input is a tty by default" do
+      source = <<~EOM
+        class OH
+          def hello
+          def hai
+          end
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+
+      io = StringIO.new
+      def io.isatty
+        true
+      end
+
+      block = CodeBlock.new(lines: code_lines[1])
+      display = DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        code_lines: code_lines
+      )
+      display.call
+      expect(io.string).to include([
+        "❯ 2  ",
+        DisplayCodeWithLineNumbers::TERMINAL_HIGHLIGHT,
+        "  def hello"
+      ].join)
+
+      io = StringIO.new
+      def io.isatty
+        false
+      end
+
+      block = CodeBlock.new(lines: code_lines[1])
+      display = DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        code_lines: code_lines
+      )
+      display.call
+      expect(io.string).to include("❯ 2    def hello")
+    end
+
+    it "outputs to io when using `call`" do
+      source = <<~EOM
+        class OH
+          def hello
+          def hai
+          end
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+
+      io = StringIO.new
+      block = CodeBlock.new(lines: code_lines[1])
+      display = DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        terminal: false,
+        code_lines: code_lines
+      )
+      display.call
+      expect(io.string).to include("❯ 2    def hello")
+    end
+
+    it " wraps code with github style codeblocks" do
+      source = <<~EOM
+        class OH
+          def hello
+
+          def hai
+          end
+        end
+      EOM
+
+      code_lines = CleanDocument.new(source: source).call.lines
+      block = CodeBlock.new(lines: code_lines[1])
+      io = StringIO.new
+      DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        terminal: false,
+        code_lines: code_lines
+      ).call
+      expect(io.string).to include(<<~EOM)
+          1  class OH
+        ❯ 2    def hello
+          4    def hai
+          5    end
+          6  end
+      EOM
+    end
+
+    it "shows terminal characters" do
+      code_lines = code_line_array(<<~EOM)
+        class OH
+          def hello
+          def hai
+          end
+        end
+      EOM
+
+      io = StringIO.new
+      block = CodeBlock.new(lines: code_lines[1])
+      DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        terminal: false,
+        code_lines: code_lines
+      ).call
+
+      expect(io.string).to include([
+        "  1  class OH",
+        "❯ 2    def hello",
+        "  4    end",
+        "  5  end",
+        ""
+      ].join($/))
+
+      block = CodeBlock.new(lines: code_lines[1])
+      io = StringIO.new
+      DisplayInvalidBlocks.new(
+        io: io,
+        blocks: block,
+        terminal: true,
+        code_lines: code_lines
+      ).call
+
+      expect(io.string).to include(
+        [
+          "  1  class OH",
+          ["❯ 2  ", DisplayCodeWithLineNumbers::TERMINAL_HIGHLIGHT, "  def hello"].join,
+          "  4    end",
+          "  5  end",
+          ""
+        ].join($/ + DisplayCodeWithLineNumbers::TERMINAL_END)
+      )
+    end
+  end
+end

spec/syntax_suggest/unit/explain_syntax_spec.rb

@@ -0,0 +1,255 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "ExplainSyntax" do
+    it "handles shorthand syntaxes with non-bracket characters" do
+      source = <<~EOM
+        %Q* lol
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([])
+      expect(explain.errors.join).to include("unterminated string")
+    end
+
+    it "handles %w[]" do
+      source = <<~EOM
+        node.is_a?(Op) && %w[| ||].include?(node.value) &&
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([])
+    end
+
+    it "doesn't falsely identify strings or symbols as critical chars" do
+      source = <<~EOM
+        a = ['(', '{', '[', '|']
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([])
+
+      source = <<~EOM
+        a = [:'(', :'{', :'[', :'|']
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([])
+    end
+
+    it "finds missing |" do
+      source = <<~EOM
+        Foo.call do |
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["|"])
+      expect(explain.errors).to eq([explain.why("|")])
+    end
+
+    it "finds missing {" do
+      source = <<~EOM
+        class Cat
+          lol = {
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["}"])
+      expect(explain.errors).to eq([explain.why("}")])
+    end
+
+    it "finds missing }" do
+      source = <<~EOM
+        def foo
+          lol = "foo" => :bar }
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["{"])
+      expect(explain.errors).to eq([explain.why("{")])
+    end
+
+    it "finds missing [" do
+      source = <<~EOM
+        class Cat
+          lol = [
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["]"])
+      expect(explain.errors).to eq([explain.why("]")])
+    end
+
+    it "finds missing ]" do
+      source = <<~EOM
+        def foo
+          lol = ]
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["["])
+      expect(explain.errors).to eq([explain.why("[")])
+    end
+
+    it "finds missing (" do
+      source = "def initialize; ); end"
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["("])
+      expect(explain.errors).to eq([explain.why("(")])
+    end
+
+    it "finds missing )" do
+      source = "def initialize; (; end"
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([")"])
+      expect(explain.errors).to eq([explain.why(")")])
+    end
+
+    it "finds missing keyword" do
+      source = <<~EOM
+        class Cat
+          end
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["keyword"])
+      expect(explain.errors).to eq([explain.why("keyword")])
+    end
+
+    it "finds missing end" do
+      source = <<~EOM
+        class Cat
+          def meow
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["end"])
+      expect(explain.errors).to eq([explain.why("end")])
+    end
+
+    it "falls back to ripper on unknown errors" do
+      source = <<~EOM
+        class Cat
+          def meow
+            1 *
+          end
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq([])
+      expect(explain.errors).to eq(RipperErrors.new(source).call.errors)
+    end
+
+    it "handles an unexpected rescue" do
+      source = <<~EOM
+        def foo
+          if bar
+            "baz"
+          else
+            "foo"
+        rescue FooBar
+          nil
+        end
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["end"])
+    end
+
+    # String embeds are `"#{foo} <-- here`
+    #
+    # We need to count a `#{` as a `{`
+    # otherwise it will report that we are
+    # missing a curly when we are using valid
+    # string embed syntax
+    it "is not confused by valid string embed" do
+      source = <<~'EOM'
+        foo = "#{hello}"
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+      expect(explain.missing).to eq([])
+    end
+
+    # Missing string embed beginnings are not a
+    # syntax error. i.e. `"foo}"` or `"{foo}` or "#foo}"
+    # would just be strings with extra characters.
+    #
+    # However missing the end curly will trigger
+    # an error: i.e. `"#{foo`
+    #
+    # String embed beginning is a `#{` rather than
+    # a `{`, make sure we handle that case and
+    # report the correct missing `}` diagnosis
+    it "finds missing string embed end" do
+      source = <<~'EOM'
+        "#{foo
+      EOM
+
+      explain = ExplainSyntax.new(
+        code_lines: CodeLine.from_source(source)
+      ).call
+
+      expect(explain.missing).to eq(["}"])
+    end
+  end
+end

spec/syntax_suggest/unit/lex_all_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "EndBlockParse" do
+    it "finds blocks based on `end` keyword" do
+      source = <<~EOM
+        describe "cat" # 1
+          Cat.call do  # 2
+          end          # 3
+        end            # 4
+                       # 5
+        it "dog" do    # 6
+          Dog.call do  # 7
+          end          # 8
+        end            # 9
+      EOM
+
+      # raw_lex = Ripper.lex(source)
+      # expect(raw_lex.to_s).to_not include("dog")
+
+      lex = LexAll.new(source: source)
+      expect(lex.map(&:token).to_s).to include("dog")
+      expect(lex.first.line).to eq(1)
+      expect(lex.last.line).to eq(9)
+    end
+  end
+end

spec/syntax_suggest/unit/pathname_from_message_spec.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  RSpec.describe "PathnameFromMessage" do
+    it "handles filenames with colons in them" do
+      Dir.mktmpdir do |dir|
+        dir = Pathname(dir)
+
+        file = dir.join("scr:atch.rb").tap { |p| FileUtils.touch(p) }
+
+        message = "#{file}:2:in `require_relative': /private/tmp/bad.rb:1: syntax error, unexpected `end' (SyntaxError)"
+        file = PathnameFromMessage.new(message).call.name
+
+        expect(file).to be_truthy
+      end
+    end
+
+    it "checks if the file exists" do
+      Dir.mktmpdir do |dir|
+        dir = Pathname(dir)
+
+        file = dir.join("scratch.rb")
+        # No touch, file does not exist
+        expect(file.exist?).to be_falsey
+
+        message = "#{file}:2:in `require_relative': /private/tmp/bad.rb:1: syntax error, unexpected `end' (SyntaxError)"
+        io = StringIO.new
+        file = PathnameFromMessage.new(message, io: io).call.name
+
+        expect(io.string).to include(file.to_s)
+        expect(file).to be_falsey
+      end
+    end
+
+    it "does not output error message on syntax error inside of an (eval)" do
+      message = "(eval):1: invalid multibyte char (UTF-8) (SyntaxError)\n"
+      io = StringIO.new
+      file = PathnameFromMessage.new(message, io: io).call.name
+
+      expect(io.string).to eq("")
+      expect(file).to be_falsey
+    end
+
+    it "does not output error message on syntax error inside of streamed code" do
+      # An example of streamed code is: $ echo "def foo" | ruby
+      message = "-:1: syntax error, unexpected end-of-input\n"
+      io = StringIO.new
+      file = PathnameFromMessage.new(message, io: io).call.name
+
+      expect(io.string).to eq("")
+      expect(file).to be_falsey
+    end
+  end
+end

spec/syntax_suggest/unit/priority_queue_spec.rb

@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+module SyntaxSuggest
+  class CurrentIndex
+    attr_reader :current_indent
+
+    def initialize(value)
+      @current_indent = value
+    end
+
+    def <=>(other)
+      @current_indent <=> other.current_indent
+    end
+
+    def inspect
+      @current_indent
+    end
+  end
+
+  RSpec.describe CodeFrontier do
+    it "works" do
+      q = PriorityQueue.new
+      q << 1
+      q << 2
+      expect(q.elements).to eq([2, 1])
+
+      q << 3
+      expect(q.elements).to eq([3, 1, 2])
+
+      expect(q.pop).to eq(3)
+      expect(q.pop).to eq(2)
+      expect(q.pop).to eq(1)
+      expect(q.pop).to eq(nil)
+
+      array = []
+      q = PriorityQueue.new
+      array.reverse_each do |v|
+        q << v
+      end
+      expect(q.elements).to eq(array)
+
+      array = [100, 36, 17, 19, 25, 0, 3, 1, 7, 2]
+      array.reverse_each do |v|
+        q << v
+      end
+
+      expect(q.pop).to eq(100)
+      expect(q.elements).to eq([36, 25, 19, 17, 0, 1, 7, 2, 3])
+
+      # expected [36, 25, 19, 17, 0, 1, 7, 2, 3]
+      expect(q.pop).to eq(36)
+      expect(q.pop).to eq(25)
+      expect(q.pop).to eq(19)
+      expect(q.pop).to eq(17)
+      expect(q.pop).to eq(7)
+      expect(q.pop).to eq(3)
+      expect(q.pop).to eq(2)
+      expect(q.pop).to eq(1)
+      expect(q.pop).to eq(0)
+      expect(q.pop).to eq(nil)
+    end
+
+    it "priority queue" do
+      frontier = PriorityQueue.new
+      frontier << CurrentIndex.new(0)
+      frontier << CurrentIndex.new(1)
+
+      expect(frontier.sorted.map(&:current_indent)).to eq([0, 1])
+
+      frontier << CurrentIndex.new(1)
+      expect(frontier.sorted.map(&:current_indent)).to eq([0, 1, 1])
+
+      frontier << CurrentIndex.new(0)
+      expect(frontier.sorted.map(&:current_indent)).to eq([0, 0, 1, 1])
+
+      frontier << CurrentIndex.new(10)
+      expect(frontier.sorted.map(&:current_indent)).to eq([0, 0, 1, 1, 10])
+
+      frontier << CurrentIndex.new(2)
+      expect(frontier.sorted.map(&:current_indent)).to eq([0, 0, 1, 1, 2, 10])
+
+      frontier = PriorityQueue.new
+      values = [18, 18, 0, 18, 0, 18, 18, 18, 18, 16, 18, 8, 18, 8, 8, 8, 16, 6, 0, 0, 16, 16, 4, 14, 14, 12, 12, 12, 10, 12, 12, 12, 12, 8, 10, 10, 8, 8, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 8, 10, 6, 6, 6, 6, 6, 6, 8, 10, 8, 8, 10, 8, 10, 8, 10, 8, 6, 8, 8, 6, 8, 6, 6, 8, 0, 8, 0, 0, 8, 8, 0, 8, 0, 8, 8, 0, 8, 8, 8, 0, 8, 0, 8, 8, 8, 8, 8, 8, 8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8, 6, 8, 6, 6, 6, 6, 8, 6, 8, 6, 6, 4, 4, 6, 6, 4, 6, 4, 6, 6, 4, 6, 4, 4, 6, 6, 6, 6, 4, 4, 4, 2, 4, 4, 4, 4, 4, 4, 6, 6, 0, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 0, 0, 6, 6, 2]
+
+      values.each do |v|
+        value = CurrentIndex.new(v)
+        frontier << value # CurrentIndex.new(v)
+      end
+
+      expect(frontier.sorted.map(&:current_indent)).to eq(values.sort)
+    end
+  end
+end