1 files changed, 249 insertions, 0 deletions
diff --git a/lib/rubygems/commands/exec_command.rb b/lib/rubygems/commands/exec_command.rb
new file mode 100644
index 0000000000..d588804290
--- /dev/null
+++ b/lib/rubygems/commands/exec_command.rb
@@ -0,0 +1,249 @@
+# frozen_string_literal: true
+
+require_relative "../command"
+require_relative "../dependency_installer"
+require_relative "../gem_runner"
+require_relative "../package"
+require_relative "../version_option"
+
+class Gem::Commands::ExecCommand < Gem::Command
+  include Gem::VersionOption
+
+  def initialize
+    super "exec", "Run a command from a gem", {
+      version: Gem::Requirement.default,
+    }
+
+    add_version_option
+    add_prerelease_option "to be installed"
+
+    add_option "-g", "--gem GEM", "run the executable from the given gem" do |value, options|
+      options[:gem_name] = value
+    end
+
+    add_option(:"Install/Update", "--conservative",
+      "Prefer the most recent installed version, ",
+      "rather than the latest version overall") do |_value, options|
+      options[:conservative] = true
+    end
+  end
+
+  def arguments # :nodoc:
+    "COMMAND  the executable command to run"
+  end
+
+  def defaults_str # :nodoc:
+    "--version '#{Gem::Requirement.default}'"
+  end
+
+  def description # :nodoc:
+    <<-EOF
+The exec command handles installing (if necessary) and running an executable
+from a gem, regardless of whether that gem is currently installed.
+
+The exec command can be thought of as a shortcut to running `gem install` and
+then the executable from the installed gem.
+
+For example, `gem exec rails new .` will run `rails new .` in the current
+directory, without having to manually run `gem install rails`.
+Additionally, the exec command ensures the most recent version of the gem
+is used (unless run with `--conservative`), and that the gem is not installed
+to the same gem path as user-installed gems.
+    EOF
+  end
+
+  def usage # :nodoc:
+    "#{program_name} [options --] COMMAND [args]"
+  end
+
+  def execute
+    gem_paths = { "GEM_HOME" => Gem.paths.home, "GEM_PATH" => Gem.paths.path.join(File::PATH_SEPARATOR), "GEM_SPEC_CACHE" => Gem.paths.spec_cache_dir }.compact
+
+    check_executable
+
+    print_command
+    if options[:gem_name] == "gem" && options[:executable] == "gem"
+      set_gem_exec_install_paths
+      Gem::GemRunner.new.run options[:args]
+      return
+    elsif options[:conservative]
+      install_if_needed
+    else
+      install
+      activate!
+    end
+
+    load!
+  ensure
+    ENV.update(gem_paths) if gem_paths
+    Gem.clear_paths
+  end
+
+  private
+
+  def handle_options(args)
+    args = add_extra_args(args)
+    check_deprecated_options(args)
+    @options = Marshal.load Marshal.dump @defaults # deep copy
+    parser.order!(args) do |v|
+      # put the non-option back at the front of the list of arguments
+      args.unshift(v)
+
+      # stop parsing once we hit the first non-option,
+      # so you can call `gem exec rails --version` and it prints the rails
+      # version rather than rubygem's
+      break
+    end
+    @options[:args] = args
+
+    options[:executable], gem_version = extract_gem_name_and_version(options[:args].shift)
+    options[:gem_name] ||= options[:executable]
+
+    if gem_version
+      if options[:version].none?
+        options[:version] = Gem::Requirement.new(gem_version)
+      else
+        options[:version].concat [gem_version]
+      end
+    end
+
+    if options[:prerelease] && !options[:version].prerelease?
+      if options[:version].none?
+        options[:version] = Gem::Requirement.default_prerelease
+      else
+        options[:version].concat [Gem::Requirement.default_prerelease]
+      end
+    end
+  end
+
+  def check_executable
+    if options[:executable].nil?
+      raise Gem::CommandLineError,
+        "Please specify an executable to run (e.g. #{program_name} COMMAND)"
+    end
+  end
+
+  def print_command
+    verbose "running #{program_name} with:\n"
+    opts = options.reject {|_, v| v.nil? || Array(v).empty? }
+    max_length = opts.map {|k, _| k.size }.max
+    opts.each do |k, v|
+      next if v.nil?
+      verbose "\t#{k.to_s.rjust(max_length)}: #{v}"
+    end
+    verbose ""
+  end
+
+  def install_if_needed
+    activate!
+  rescue Gem::MissingSpecError
+    verbose "#{Gem::Dependency.new(options[:gem_name], options[:version])} not available locally, installing from remote"
+    install
+    activate!
+  end
+
+  def set_gem_exec_install_paths
+    home = File.join(Gem.dir, "gem_exec")
+
+    ENV["GEM_PATH"] = ([home] + Gem.path).join(File::PATH_SEPARATOR)
+    ENV["GEM_HOME"] = home
+    Gem.clear_paths
+  end
+
+  def install
+    set_gem_exec_install_paths
+
+    gem_name = options[:gem_name]
+    gem_version = options[:version]
+
+    install_options = options.merge(
+      minimal_deps: false,
+      wrappers: true
+    )
+
+    suppress_always_install do
+      dep_installer = Gem::DependencyInstaller.new install_options
+
+      request_set = dep_installer.resolve_dependencies gem_name, gem_version
+
+      verbose "Gems to install:"
+      request_set.sorted_requests.each do |activation_request|
+        verbose "\t#{activation_request.full_name}"
+      end
+
+      request_set.install install_options
+    end
+
+    Gem::Specification.reset
+  rescue Gem::InstallError => e
+    alert_error "Error installing #{gem_name}:\n\t#{e.message}"
+    terminate_interaction 1
+  rescue Gem::GemNotFoundException => e
+    show_lookup_failure e.name, e.version, e.errors, false
+
+    terminate_interaction 2
+  rescue Gem::UnsatisfiableDependencyError => e
+    show_lookup_failure e.name, e.version, e.errors, false,
+                        "'#{gem_name}' (#{gem_version})"
+
+    terminate_interaction 2
+  end
+
+  def activate!
+    gem(options[:gem_name], options[:version])
+    Gem.finish_resolve
+
+    verbose "activated #{options[:gem_name]} (#{Gem.loaded_specs[options[:gem_name]].version})"
+  end
+
+  def load!
+    argv = ARGV.clone
+    ARGV.replace options[:args]
+
+    exe = executable = options[:executable]
+
+    contains_executable = Gem.loaded_specs.values.select do |spec|
+      spec.executables.include?(executable)
+    end
+
+    if contains_executable.any? {|s| s.name == executable }
+      contains_executable.select! {|s| s.name == executable }
+    end
+
+    if contains_executable.empty?
+      if (spec = Gem.loaded_specs[executable]) && (exe = spec.executable)
+        contains_executable << spec
+      else
+        alert_error "Failed to load executable `#{executable}`," \
+              " are you sure the gem `#{options[:gem_name]}` contains it?"
+        terminate_interaction 1
+      end
+    end
+
+    if contains_executable.size > 1
+      alert_error "Ambiguous which gem `#{executable}` should come from: " \
+            "the options are #{contains_executable.map(&:name)}, " \
+            "specify one via `-g`"
+      terminate_interaction 1
+    end
+
+    load Gem.activate_bin_path(contains_executable.first.name, exe, ">= 0.a")
+  ensure
+    ARGV.replace argv
+  end
+
+  def suppress_always_install
+    name = :always_install
+    cls = ::Gem::Resolver::InstallerSet
+    method = cls.instance_method(name)
+    cls.remove_method(name)
+    cls.define_method(name) { [] }
+
+    begin
+      yield
+    ensure
+      cls.remove_method(name)
+      cls.define_method(name, method)
+    end
+  end
+end