[rubygems/rubygems] Use a constant empty tar header to avoid extra allocations

[ruby.git] / lib / erb.rb

# -*- coding: us-ascii -*-
# frozen_string_literal: true
# = ERB -- Ruby Templating
#
# Author:: Masatoshi SEKI
# Documentation:: James Edward Gray II, Gavin Sinclair, and Simon Chiang
#
# See ERB for primary documentation and ERB::Util for a couple of utility
# routines.
#
# Copyright (c) 1999-2000,2002,2003 Masatoshi SEKI
#
# You can redistribute it and/or modify it under the same terms as Ruby.

require 'cgi/util'
require 'erb/version'
require 'erb/compiler'
require 'erb/def_method'
require 'erb/util'

#
# = ERB -- Ruby Templating
#
# == Introduction
#
# ERB provides an easy to use but powerful templating system for Ruby.  Using
# ERB, actual Ruby code can be added to any plain text document for the
# purposes of generating document information details and/or flow control.
#
# A very simple example is this:
#
#   require 'erb'
#
#   x = 42
#   template = ERB.new <<-EOF
#     The value of x is: <%= x %>
#   EOF
#   puts template.result(binding)
#
# <em>Prints:</em> The value of x is: 42
#
# More complex examples are given below.
#
#
# == Recognized Tags
#
# ERB recognizes certain tags in the provided template and converts them based
# on the rules below:
#
#   <% Ruby code -- inline with output %>
#   <%= Ruby expression -- replace with result %>
#   <%# comment -- ignored -- useful in testing %> (`<% #` doesn't work. Don't use Ruby comments.)
#   % a line of Ruby code -- treated as <% line %> (optional -- see ERB.new)
#   %% replaced with % if first thing on a line and % processing is used
#   <%% or %%> -- replace with <% or %> respectively
#
# All other text is passed through ERB filtering unchanged.
#
#
# == Options
#
# There are several settings you can change when you use ERB:
# * the nature of the tags that are recognized;
# * the binding used to resolve local variables in the template.
#
# See the ERB.new and ERB#result methods for more detail.
#
# == Character encodings
#
# ERB (or Ruby code generated by ERB) returns a string in the same
# character encoding as the input string.  When the input string has
# a magic comment, however, it returns a string in the encoding specified
# by the magic comment.
#
#   # -*- coding: utf-8 -*-
#   require 'erb'
#
#   template = ERB.new <<EOF
#   <%#-*- coding: Big5 -*-%>
#     \_\_ENCODING\_\_ is <%= \_\_ENCODING\_\_ %>.
#   EOF
#   puts template.result
#
# <em>Prints:</em> \_\_ENCODING\_\_ is Big5.
#
#
# == Examples
#
# === Plain Text
#
# ERB is useful for any generic templating situation.  Note that in this example, we use the
# convenient "% at start of line" tag, and we quote the template literally with
# <tt>%q{...}</tt> to avoid trouble with the backslash.
#
#   require "erb"
#
#   # Create template.
#   template = %q{
#     From:  James Edward Gray II <james@grayproductions.net>
#     To:  <%= to %>
#     Subject:  Addressing Needs
#
#     <%= to[/\w+/] %>:
#
#     Just wanted to send a quick note assuring that your needs are being
#     addressed.
#
#     I want you to know that my team will keep working on the issues,
#     especially:
#
#     <%# ignore numerous minor requests -- focus on priorities %>
#     % priorities.each do |priority|
#       * <%= priority %>
#     % end
#
#     Thanks for your patience.
#
#     James Edward Gray II
#   }.gsub(/^  /, '')
#
#   message = ERB.new(template, trim_mode: "%<>")
#
#   # Set up template data.
#   to = "Community Spokesman <spokesman@ruby_community.org>"
#   priorities = [ "Run Ruby Quiz",
#                  "Document Modules",
#                  "Answer Questions on Ruby Talk" ]
#
#   # Produce result.
#   email = message.result
#   puts email
#
# <i>Generates:</i>
#
#   From:  James Edward Gray II <james@grayproductions.net>
#   To:  Community Spokesman <spokesman@ruby_community.org>
#   Subject:  Addressing Needs
#
#   Community:
#
#   Just wanted to send a quick note assuring that your needs are being addressed.
#
#   I want you to know that my team will keep working on the issues, especially:
#
#       * Run Ruby Quiz
#       * Document Modules
#       * Answer Questions on Ruby Talk
#
#   Thanks for your patience.
#
#   James Edward Gray II
#
# === Ruby in HTML
#
# ERB is often used in <tt>.rhtml</tt> files (HTML with embedded Ruby).  Notice the need in
# this example to provide a special binding when the template is run, so that the instance
# variables in the Product object can be resolved.
#
#   require "erb"
#
#   # Build template data class.
#   class Product
#     def initialize( code, name, desc, cost )
#       @code = code
#       @name = name
#       @desc = desc
#       @cost = cost
#
#       @features = [ ]
#     end
#
#     def add_feature( feature )
#       @features << feature
#     end
#
#     # Support templating of member data.
#     def get_binding
#       binding
#     end
#
#     # ...
#   end
#
#   # Create template.
#   template = %{
#     <html>
#       <head><title>Ruby Toys -- <%= @name %></title></head>
#       <body>
#
#         <h1><%= @name %> (<%= @code %>)</h1>
#         <p><%= @desc %></p>
#
#         <ul>
#           <% @features.each do |f| %>
#             <li><b><%= f %></b></li>
#           <% end %>
#         </ul>
#
#         <p>
#           <% if @cost < 10 %>
#             <b>Only <%= @cost %>!!!</b>
#           <% else %>
#              Call for a price, today!
#           <% end %>
#         </p>
#
#       </body>
#     </html>
#   }.gsub(/^  /, '')
#
#   rhtml = ERB.new(template)
#
#   # Set up template data.
#   toy = Product.new( "TZ-1002",
#                      "Rubysapien",
#                      "Geek's Best Friend!  Responds to Ruby commands...",
#                      999.95 )
#   toy.add_feature("Listens for verbal commands in the Ruby language!")
#   toy.add_feature("Ignores Perl, Java, and all C variants.")
#   toy.add_feature("Karate-Chop Action!!!")
#   toy.add_feature("Matz signature on left leg.")
#   toy.add_feature("Gem studded eyes... Rubies, of course!")
#
#   # Produce result.
#   rhtml.run(toy.get_binding)
#
# <i>Generates (some blank lines removed):</i>
#
#    <html>
#      <head><title>Ruby Toys -- Rubysapien</title></head>
#      <body>
#
#        <h1>Rubysapien (TZ-1002)</h1>
#        <p>Geek's Best Friend!  Responds to Ruby commands...</p>
#
#        <ul>
#            <li><b>Listens for verbal commands in the Ruby language!</b></li>
#            <li><b>Ignores Perl, Java, and all C variants.</b></li>
#            <li><b>Karate-Chop Action!!!</b></li>
#            <li><b>Matz signature on left leg.</b></li>
#            <li><b>Gem studded eyes... Rubies, of course!</b></li>
#        </ul>
#
#        <p>
#             Call for a price, today!
#        </p>
#
#      </body>
#    </html>
#
#
# == Notes
#
# There are a variety of templating solutions available in various Ruby projects.
# For example, RDoc, distributed with Ruby, uses its own template engine, which
# can be reused elsewhere.
#
# Other popular engines could be found in the corresponding
# {Category}[https://www.ruby-toolbox.com/categories/template_engines] of
# The Ruby Toolbox.
#
class ERB
  Revision = '$Date::                           $' # :nodoc: #'
  deprecate_constant :Revision

  # Returns revision information for the erb.rb module.
  def self.version
    VERSION
  end

  #
  # Constructs a new ERB object with the template specified in _str_.
  #
  # An ERB object works by building a chunk of Ruby code that will output
  # the completed template when run.
  #
  # If _trim_mode_ is passed a String containing one or more of the following
  # modifiers, ERB will adjust its code generation as listed:
  #
  #     %  enables Ruby code processing for lines beginning with %
  #     <> omit newline for lines starting with <% and ending in %>
  #     >  omit newline for lines ending in %>
  #     -  omit blank lines ending in -%>
  #
  # _eoutvar_ can be used to set the name of the variable ERB will build up
  # its output in.  This is useful when you need to run multiple ERB
  # templates through the same binding and/or when you want to control where
  # output ends up.  Pass the name of the variable to be used inside a String.
  #
  # === Example
  #
  #  require "erb"
  #
  #  # build data class
  #  class Listings
  #    PRODUCT = { :name => "Chicken Fried Steak",
  #                :desc => "A well messages pattie, breaded and fried.",
  #                :cost => 9.95 }
  #
  #    attr_reader :product, :price
  #
  #    def initialize( product = "", price = "" )
  #      @product = product
  #      @price = price
  #    end
  #
  #    def build
  #      b = binding
  #      # create and run templates, filling member data variables
  #      ERB.new(<<~'END_PRODUCT', trim_mode: "", eoutvar: "@product").result b
  #        <%= PRODUCT[:name] %>
  #        <%= PRODUCT[:desc] %>
  #      END_PRODUCT
  #      ERB.new(<<~'END_PRICE', trim_mode: "", eoutvar: "@price").result b
  #        <%= PRODUCT[:name] %> -- <%= PRODUCT[:cost] %>
  #        <%= PRODUCT[:desc] %>
  #      END_PRICE
  #    end
  #  end
  #
  #  # setup template data
  #  listings = Listings.new
  #  listings.build
  #
  #  puts listings.product + "\n" + listings.price
  #
  # _Generates_
  #
  #  Chicken Fried Steak
  #  A well messages pattie, breaded and fried.
  #
  #  Chicken Fried Steak -- 9.95
  #  A well messages pattie, breaded and fried.
  #
  def initialize(str, safe_level=NOT_GIVEN, legacy_trim_mode=NOT_GIVEN, legacy_eoutvar=NOT_GIVEN, trim_mode: nil, eoutvar: '_erbout')
    # Complex initializer for $SAFE deprecation at [Feature #14256]. Use keyword arguments to pass trim_mode or eoutvar.
    if safe_level != NOT_GIVEN
      warn 'Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.', uplevel: 1
    end
    if legacy_trim_mode != NOT_GIVEN
      warn 'Passing trim_mode with the 3rd argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode: ...) instead.', uplevel: 1
      trim_mode = legacy_trim_mode
    end
    if legacy_eoutvar != NOT_GIVEN
      warn 'Passing eoutvar with the 4th argument of ERB.new is deprecated. Use keyword argument like ERB.new(str, eoutvar: ...) instead.', uplevel: 1
      eoutvar = legacy_eoutvar
    end

    compiler = make_compiler(trim_mode)
    set_eoutvar(compiler, eoutvar)
    @src, @encoding, @frozen_string = *compiler.compile(str)
    @filename = nil
    @lineno = 0
    @_init = self.class.singleton_class
  end
  NOT_GIVEN = Object.new
  private_constant :NOT_GIVEN

  ##
  # Creates a new compiler for ERB.  See ERB::Compiler.new for details

  def make_compiler(trim_mode)
    ERB::Compiler.new(trim_mode)
  end

  # The Ruby code generated by ERB
  attr_reader :src

  # The encoding to eval
  attr_reader :encoding

  # The optional _filename_ argument passed to Kernel#eval when the ERB code
  # is run
  attr_accessor :filename

  # The optional _lineno_ argument passed to Kernel#eval when the ERB code
  # is run
  attr_accessor :lineno

  #
  # Sets optional filename and line number that will be used in ERB code
  # evaluation and error reporting. See also #filename= and #lineno=
  #
  #   erb = ERB.new('<%= some_x %>')
  #   erb.render
  #   # undefined local variable or method `some_x'
  #   #   from (erb):1
  #
  #   erb.location = ['file.erb', 3]
  #   # All subsequent error reporting would use new location
  #   erb.render
  #   # undefined local variable or method `some_x'
  #   #   from file.erb:4
  #
  def location=((filename, lineno))
    @filename = filename
    @lineno = lineno if lineno
  end

  #
  # Can be used to set _eoutvar_ as described in ERB::new.  It's probably
  # easier to just use the constructor though, since calling this method
  # requires the setup of an ERB _compiler_ object.
  #
  def set_eoutvar(compiler, eoutvar = '_erbout')
    compiler.put_cmd = "#{eoutvar}.<<"
    compiler.insert_cmd = "#{eoutvar}.<<"
    compiler.pre_cmd = ["#{eoutvar} = +''"]
    compiler.post_cmd = [eoutvar]
  end

  # Generate results and print them. (see ERB#result)
  def run(b=new_toplevel)
    print self.result(b)
  end

  #
  # Executes the generated ERB code to produce a completed template, returning
  # the results of that code.  (See ERB::new for details on how this process
  # can be affected by _safe_level_.)
  #
  # _b_ accepts a Binding object which is used to set the context of
  # code evaluation.
  #
  def result(b=new_toplevel)
    unless @_init.equal?(self.class.singleton_class)
      raise ArgumentError, "not initialized"
    end
    eval(@src, b, (@filename || '(erb)'), @lineno)
  end

  # Render a template on a new toplevel binding with local variables specified
  # by a Hash object.
  def result_with_hash(hash)
    b = new_toplevel(hash.keys)
    hash.each_pair do |key, value|
      b.local_variable_set(key, value)
    end
    result(b)
  end

  ##
  # Returns a new binding each time *near* TOPLEVEL_BINDING for runs that do
  # not specify a binding.

  def new_toplevel(vars = nil)
    b = TOPLEVEL_BINDING
    if vars
      vars = vars.select {|v| b.local_variable_defined?(v)}
      unless vars.empty?
        return b.eval("tap {|;#{vars.join(',')}| break binding}")
      end
    end
    b.dup
  end
  private :new_toplevel

  # Define _methodname_ as instance method of _mod_ from compiled Ruby source.
  #
  # example:
  #   filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
  #   erb = ERB.new(File.read(filename))
  #   erb.def_method(MyClass, 'render(arg1, arg2)', filename)
  #   print MyClass.new.render('foo', 123)
  def def_method(mod, methodname, fname='(ERB)')
    src = self.src.sub(/^(?!#|$)/) {"def #{methodname}\n"} << "\nend\n"
    mod.module_eval do
      eval(src, binding, fname, -1)
    end
  end

  # Create unnamed module, define _methodname_ as instance method of it, and return it.
  #
  # example:
  #   filename = 'example.rhtml'   # 'arg1' and 'arg2' are used in example.rhtml
  #   erb = ERB.new(File.read(filename))
  #   erb.filename = filename
  #   MyModule = erb.def_module('render(arg1, arg2)')
  #   class MyClass
  #     include MyModule
  #   end
  def def_module(methodname='erb')
    mod = Module.new
    def_method(mod, methodname, @filename || '(ERB)')
    mod
  end

  # Define unnamed class which has _methodname_ as instance method, and return it.
  #
  # example:
  #   class MyClass_
  #     def initialize(arg1, arg2)
  #       @arg1 = arg1;  @arg2 = arg2
  #     end
  #   end
  #   filename = 'example.rhtml'  # @arg1 and @arg2 are used in example.rhtml
  #   erb = ERB.new(File.read(filename))
  #   erb.filename = filename
  #   MyClass = erb.def_class(MyClass_, 'render()')
  #   print MyClass.new('foo', 123).render()
  def def_class(superklass=Object, methodname='result')
    cls = Class.new(superklass)
    def_method(cls, methodname, @filename || '(ERB)')
    cls
  end
end