SASS forking to override paths

example.scss

@path '("bootstrap": "../components/bootstrap-sass/vendor/assets/stylesheets/bootstrap")';
@import  "bootstrap";

import.rb

#sass{$version}/lib/sass/tree/import_node.rb
module Sass
  module Tree
    # A static node that wraps the {Sass::Tree} for an `@import`ed file.
    # It doesn't have a functional purpose other than to add the `@import`ed file
    # to the backtrace if an error occurs.
    class ImportNode < RootNode
      # The name of the imported file as it appears in the Sass document.
      #
      # @return [String]
      attr_reader :imported_filename

      # Sets the imported file.
      attr_writer :imported_file

      attr_accessor :immutable_path

      # @param imported_filename [String] The name of the imported file
      def initialize(imported_filename)
        @imported_filename = imported_filename
        super(nil)
      end

      def invisible?; to_s.empty?; end

      # Returns the imported file.
      #
      # @return [Sass::Engine]
      # @raise [Sass::SyntaxError] If no file could be found to import.
      def imported_file
        @imported_file ||= import
      end

      # Returns whether or not this import should emit a CSS @import declaration
      #
      # @return [Boolean] Whether or not this is a simple CSS @import declaration.
      def css_import?(immutable_path = {})
        self.immutable_path = immutable_path
        self.immutable_path = {} if self.immutable_path.nil?
        if @imported_filename =~ /\.css$/
          @imported_filename
        elsif imported_file.is_a?(String) && imported_file =~ /\.css$/
          imported_file
        end
      end

      private

      def import
        paths = @options[:load_paths]
         
        if @options[:importer]
          if(self.immutable_path[imported_filename])
            @imported_filename = self.immutable_path[imported_filename]
          end
          f = @options[:importer].find_relative(
            @imported_filename, @options[:filename], options_for_importer)
          return f if f
        end

        paths.each do |p|
          f = p.find(@imported_filename, options_for_importer)
          return f if f
        end

        message = "File to import not found or unreadable: #{@imported_filename}.\n"
        if paths.size == 1
          message << "Load path: #{paths.first}"
        else
          message << "Load paths:\n  " << paths.join("\n  ")
        end
        raise SyntaxError.new(message)
      rescue SyntaxError => e
        raise SyntaxError.new(e.message, :line => line, :filename => @filename)
      end

      def options_for_importer
        @options.merge(:_from_import_node => true)
      end
    end
  end
end

perform.rb

#sass{$version}/lib/sass/tree/visitors/perform.rb
require "json"
# A visitor for converting a dynamic Sass tree into a static Sass tree.
class Sass::Tree::Visitors::Perform < Sass::Tree::Visitors::Base
  attr_accessor :immutable_path
  class << self
    # @param root [Tree::Node] The root node of the tree to visit.
    # @param environment [Sass::Environment] The lexical environment.
    # @return [Tree::Node] The resulting tree of static nodes.
    def visit(root, environment = nil)
      new(environment).send(:visit, root)
    end

    # @api private
    # @comment
    #   rubocop:disable MethodLength
    def perform_arguments(callable, args, splat)
      desc = "#{callable.type.capitalize} #{callable.name}"
      downcase_desc = "#{callable.type} #{callable.name}"

      # All keywords are contained in splat.keywords for consistency,
      # even if there were no splats passed in.
      old_keywords_accessed = splat.keywords_accessed
      keywords = splat.keywords
      splat.keywords_accessed = old_keywords_accessed

      begin
        unless keywords.empty?
          unknown_args = Sass::Util.array_minus(keywords.keys,
            callable.args.map {|var| var.first.underscored_name})
          if callable.splat && unknown_args.include?(callable.splat.underscored_name)
            raise Sass::SyntaxError.new("Argument $#{callable.splat.name} of #{downcase_desc} " +
                                        "cannot be used as a named argument.")
          elsif unknown_args.any?
            description = unknown_args.length > 1 ? 'the following arguments:' : 'an argument named'
            raise Sass::SyntaxError.new("#{desc} doesn't have #{description} " +
                                        "#{unknown_args.map {|name| "$#{name}"}.join ', '}.")
          end
        end
      rescue Sass::SyntaxError => keyword_exception
      end

      # If there's no splat, raise the keyword exception immediately. The actual
      # raising happens in the ensure clause at the end of this function.
      return if keyword_exception && !callable.splat

      if args.size > callable.args.size && !callable.splat
        takes = callable.args.size
        passed = args.size
        raise Sass::SyntaxError.new(
          "#{desc} takes #{takes} argument#{'s' unless takes == 1} " +
          "but #{passed} #{passed == 1 ? 'was' : 'were'} passed.")
      end

      splat_sep = :comma
      if splat
        args += splat.to_a
        splat_sep = splat.separator
      end

      env = Sass::Environment.new(callable.environment)
      callable.args.zip(args[0...callable.args.length]) do |(var, default), value|
        if value && keywords.has_key?(var.name)
          raise Sass::SyntaxError.new("#{desc} was passed argument $#{var.name} " +
                                      "both by position and by name.")
        end

        value ||= keywords.delete(var.name)
        value ||= default && default.perform(env)
        raise Sass::SyntaxError.new("#{desc} is missing argument #{var.inspect}.") unless value
        env.set_local_var(var.name, value)
      end

      if callable.splat
        rest = args[callable.args.length..-1] || []
        arg_list = Sass::Script::Value::ArgList.new(rest, keywords, splat_sep)
        arg_list.options = env.options
        env.set_local_var(callable.splat.name, arg_list)
      end

      yield env
    rescue StandardError => e
    ensure
      # If there's a keyword exception, we don't want to throw it immediately,
      # because the invalid keywords may be part of a glob argument that should be
      # passed on to another function. So we only raise it if we reach the end of
      # this function *and* the keywords attached to the argument list glob object
      # haven't been accessed.
      #
      # The keyword exception takes precedence over any Sass errors, but not over
      # non-Sass exceptions.
      if keyword_exception &&
          !(arg_list && arg_list.keywords_accessed) &&
          (e.nil? || e.is_a?(Sass::SyntaxError))
        raise keyword_exception
      elsif e
        raise e
      end
    end

    # @api private
    # @return [Sass::Script::Value::ArgList]
    def perform_splat(splat, performed_keywords, kwarg_splat, environment)
      args, kwargs, separator = [], nil, :comma

      if splat
        splat = splat.perform(environment)
        separator = splat.separator || separator
        if splat.is_a?(Sass::Script::Value::ArgList)
          args = splat.to_a
          kwargs = splat.keywords
        elsif splat.is_a?(Sass::Script::Value::Map)
          kwargs = arg_hash(splat)
        else
          args = splat.to_a
        end
      end
      kwargs ||= Sass::Util::NormalizedMap.new
      kwargs.update(performed_keywords)

      if kwarg_splat
        kwarg_splat = kwarg_splat.perform(environment)
        unless kwarg_splat.is_a?(Sass::Script::Value::Map)
          raise Sass::SyntaxError.new("Variable keyword arguments must be a map " +
                                      "(was #{kwarg_splat.inspect}).")
        end
        kwargs.update(arg_hash(kwarg_splat))
      end

      Sass::Script::Value::ArgList.new(args, kwargs, separator)
    end

    private

    def arg_hash(map)
      Sass::Util.map_keys(map.to_h) do |key|
        next key.value if key.is_a?(Sass::Script::Value::String)
        raise Sass::SyntaxError.new("Variable keyword argument map must have string keys.\n" +
          "#{key.inspect} is not a string in #{map.inspect}.")
      end
    end
  end
  # @comment
  #   rubocop:enable MethodLength

  protected

  def initialize(env)
    @environment = env
  end

  # If an exception is raised, this adds proper metadata to the backtrace.
  def visit(node)
    return super(node.dup) unless @environment
    @environment.stack.with_base(node.filename, node.line) {super(node.dup)}
  rescue Sass::SyntaxError => e
    e.modify_backtrace(:filename => node.filename, :line => node.line)
    raise e
  end

  # Keeps track of the current environment.
  def visit_children(parent)
    with_environment Sass::Environment.new(@environment, parent.options) do
      parent.children = super.flatten
      parent
    end
  end

  # Runs a block of code with the current environment replaced with the given one.
  #
  # @param env [Sass::Environment] The new environment for the duration of the block.
  # @yield A block in which the environment is set to `env`.
  # @return [Object] The return value of the block.
  def with_environment(env)
    old_env, @environment = @environment, env
    yield
  ensure
    @environment = old_env
  end

  # Sets the options on the environment if this is the top-level root.
  def visit_root(node)
    yield
  rescue Sass::SyntaxError => e
    e.sass_template ||= node.template
    raise e
  end

  # Removes this node from the tree if it's a silent comment.
  def visit_comment(node)
    return [] if node.invisible?
    node.resolved_value = run_interp_no_strip(node.value)
    node.resolved_value.gsub!(/\\([\\#])/, '\1')
    node
  end

  # Prints the expression to STDERR.
  def visit_debug(node)
    res = node.expr.perform(@environment)
    if res.is_a?(Sass::Script::Value::String)
      res = res.value
    else
      res = res.to_sass
    end
    if node.filename
      Sass::Util.sass_warn "#{node.filename}:#{node.line} DEBUG: #{res}"
    else
      Sass::Util.sass_warn "Line #{node.line} DEBUG: #{res}"
    end
    []
  end

  # Runs the child nodes once for each value in the list.
  def visit_each(node)
    list = node.list.perform(@environment)

    with_environment Sass::Environment.new(@environment) do
      list.to_a.map do |value|
        if node.vars.length == 1
          @environment.set_local_var(node.vars.first, value)
        else
          node.vars.zip(value.to_a) do |(var, sub_value)|
            @environment.set_local_var(var, sub_value || Sass::Script::Value::Null.new)
          end
        end
        node.children.map {|c| visit(c)}
      end.flatten
    end
  end

  # Runs SassScript interpolation in the selector,
  # and then parses the result into a {Sass::Selector::CommaSequence}.
  def visit_extend(node)
    parser = Sass::SCSS::StaticParser.new(run_interp(node.selector),
      node.filename, node.options[:importer], node.line)
    node.resolved_selector = parser.parse_selector
    node
  end

  # Runs the child nodes once for each time through the loop, varying the variable each time.
  def visit_for(node)
    from = node.from.perform(@environment)
    to = node.to.perform(@environment)
    from.assert_int!
    to.assert_int!

    to = to.coerce(from.numerator_units, from.denominator_units)
    direction = from.to_i > to.to_i ? -1 : 1
    range = Range.new(direction * from.to_i, direction * to.to_i, node.exclusive)

    with_environment Sass::Environment.new(@environment) do
      range.map do |i|
        @environment.set_local_var(node.var,
          Sass::Script::Value::Number.new(direction * i,
            from.numerator_units, from.denominator_units))
        node.children.map {|c| visit(c)}
      end.flatten
    end
  end

  # Loads the function into the environment.
  def visit_function(node)
    env = Sass::Environment.new(@environment, node.options)
    @environment.set_local_function(node.name,
      Sass::Callable.new(node.name, node.args, node.splat, env,
                         node.children, !:has_content, "function"))
    []
  end

  # Runs the child nodes if the conditional expression is true;
  # otherwise, tries the else nodes.
  def visit_if(node)
    if node.expr.nil? || node.expr.perform(@environment).to_bool
      yield
      node.children
    elsif node.else
      visit(node.else)
    else
      []
    end
  end

  # Returns a static DirectiveNode if this is importing a CSS file,
  # or parses and includes the imported Sass file.
  def visit_import(node)
    if (path = node.css_import?(@immutable_path))
      resolved_node = Sass::Tree::CssImportNode.resolved("url(#{path})")
      resolved_node.source_range = node.source_range
      return resolved_node
    end
    file = node.imported_file
    if @environment.stack.frames.any? {|f| f.is_import? && f.filename == file.options[:filename]}
      handle_import_loop!(node)
    end

    begin
      @environment.stack.with_import(node.filename, node.line) do
        root = file.to_tree
        Sass::Tree::Visitors::CheckNesting.visit(root)
        node.children = root.children.map {|c| visit(c)}.flatten
        node
      end
    rescue Sass::SyntaxError => e
      e.modify_backtrace(:filename => node.imported_file.options[:filename])
      e.add_backtrace(:filename => node.filename, :line => node.line)
      raise e
    end
  end

  # Loads a mixin into the environment.
  def visit_mixindef(node)
    env = Sass::Environment.new(@environment, node.options)
    @environment.set_local_mixin(node.name,
      Sass::Callable.new(node.name, node.args, node.splat, env,
                         node.children, node.has_content, "mixin"))
    []
  end

  # Runs a mixin.
  def visit_mixin(node)
    @environment.stack.with_mixin(node.filename, node.line, node.name) do
      mixin = @environment.mixin(node.name)
      raise Sass::SyntaxError.new("Undefined mixin '#{node.name}'.") unless mixin

      if node.children.any? && !mixin.has_content
        raise Sass::SyntaxError.new(%Q{Mixin "#{node.name}" does not accept a content block.})
      end

      args = node.args.map {|a| a.perform(@environment)}
      keywords = Sass::Util.map_vals(node.keywords) {|v| v.perform(@environment)}
      splat = self.class.perform_splat(node.splat, keywords, node.kwarg_splat, @environment)

      self.class.perform_arguments(mixin, args, splat) do |env|
        env.caller = Sass::Environment.new(@environment)
        env.content = [node.children, @environment] if node.has_children

        trace_node = Sass::Tree::TraceNode.from_node(node.name, node)
        with_environment(env) {trace_node.children = mixin.tree.map {|c| visit(c)}.flatten}
        trace_node
      end
    end
  rescue Sass::SyntaxError => e
    e.modify_backtrace(:mixin => node.name, :line => node.line)
    e.add_backtrace(:line => node.line)
    raise e
  end

  def visit_content(node)
    content, content_env = @environment.content
    return [] unless content
    @environment.stack.with_mixin(node.filename, node.line, '@content') do
      trace_node = Sass::Tree::TraceNode.from_node('@content', node)
      content_env = Sass::Environment.new(content_env)
      content_env.caller = Sass::Environment.new(@environment)
      with_environment(content_env) do
        trace_node.children = content.map {|c| visit(c.dup)}.flatten
      end
      trace_node
    end
  rescue Sass::SyntaxError => e
    e.modify_backtrace(:mixin => '@content', :line => node.line)
    e.add_backtrace(:line => node.line)
    raise e
  end

  # Runs any SassScript that may be embedded in a property.
  def visit_prop(node)
    node.resolved_name = run_interp(node.name)
    val = node.value.perform(@environment)
    node.resolved_value = val.to_s
    node.value_source_range = val.source_range if val.source_range
    yield
  end

  # Returns the value of the expression.
  def visit_return(node)
    throw :_sass_return, node.expr.perform(@environment)
  end

  # Runs SassScript interpolation in the selector,
  # and then parses the result into a {Sass::Selector::CommaSequence}.
  def visit_rule(node)
    old_at_root_without_rule, @at_root_without_rule = @at_root_without_rule, false
    parser = Sass::SCSS::StaticParser.new(run_interp(node.rule),
      node.filename, node.options[:importer], node.line)
    node.parsed_rules ||= parser.parse_selector
    node.resolved_rules = node.parsed_rules.resolve_parent_refs(
      @environment.selector, !old_at_root_without_rule)
    node.stack_trace = @environment.stack.to_s if node.options[:trace_selectors]
    with_environment Sass::Environment.new(@environment, node.options) do
      @environment.selector = node.resolved_rules
      node.children = node.children.map {|c| visit(c)}.flatten
    end
    node
  ensure
    @at_root_without_rule = old_at_root_without_rule
  end

  # Sets a variable that indicates that the first level of rule nodes
  # shouldn't include the parent selector by default.
  def visit_atroot(node)
    if node.query
      parser = Sass::SCSS::StaticParser.new(run_interp(node.query),
        node.filename, node.options[:importer], node.line)
      node.resolved_type, node.resolved_value = parser.parse_static_at_root_query
    else
      node.resolved_type, node.resolved_value = :without, ['rule']
    end

    old_at_root_without_rule = @at_root_without_rule
    @at_root_without_rule = true if node.exclude?('rule')
    yield
  ensure
    @at_root_without_rule = old_at_root_without_rule
  end

  # Loads the new variable value into the environment.
  def visit_variable(node)
    env = @environment
    identifier = [node.name, node.filename, node.line]
    if node.global
      env = env.global_env
    elsif env.parent && env.is_var_global?(node.name) &&
        !env.global_env.global_warning_given.include?(identifier)
      env.global_env.global_warning_given.add(identifier)
      var_expr = "$#{node.name}: #{node.expr.to_sass(env.options)} !global"
      var_expr << " !default" if node.guarded
      location = "on line #{node.line}"
      location << " of #{node.filename}" if node.filename
      Sass::Util.sass_warn <<WARNING
DEPRECATION WARNING #{location}:
Assigning to global variable "$#{node.name}" by default is deprecated.
In future versions of Sass, this will create a new local variable.
If you want to assign to the global variable, use "#{var_expr}" instead.
Note that this will be incompatible with Sass 3.2.
WARNING
    end

    var = env.var(node.name)
    return [] if node.guarded && var && !var.null?
    val = node.expr.perform(@environment)
    if node.expr.source_range
      val.source_range = node.expr.source_range
    else
      val.source_range = node.source_range
    end
    env.set_var(node.name, val)
    []
  end

  # Prints the expression to STDERR with a stylesheet trace.
  def visit_warn(node)
    res = node.expr.perform(@environment)
    res = res.value if res.is_a?(Sass::Script::Value::String)
    msg = "WARNING: #{res}\n         "
    msg << @environment.stack.to_s.gsub("\n", "\n         ") << "\n"
    Sass::Util.sass_warn msg
    []
  end

  # Runs the child nodes until the continuation expression becomes false.
  def visit_while(node)
    children = []
    with_environment Sass::Environment.new(@environment) do
      children += node.children.map {|c| visit(c)} while node.expr.perform(@environment).to_bool
    end
    children.flatten
  end

  def visit_directive(node)
    node.resolved_value = run_interp(node.value)
    with_environment Sass::Environment.new(@environment) do
      node.children = node.children.map {|c| visit(c)}.flatten
      node
    end
  end

  def visit_media(node)
    parser = Sass::SCSS::StaticParser.new(run_interp(node.query),
      node.filename, node.options[:importer], node.line)
    node.resolved_query ||= parser.parse_media_query_list
    yield
  end

  def visit_supports(node)
    node.condition = node.condition.deep_copy
    node.condition.perform(@environment)
    yield
  end

  def visit_cssimport(node)
    node.resolved_uri = run_interp([node.uri])
    if node.query
      parser = Sass::SCSS::StaticParser.new(run_interp(node.query),
        node.filename, node.options[:importer], node.line)
      node.resolved_query ||= parser.parse_media_query_list
    end
    yield
  end

  private

  def run_interp_no_strip(text)
    text.map do |r|
      next r if r.is_a?(String)
      val = r.perform(@environment)
      # Interpolated strings should never render with quotes
      next val.value if val.is_a?(Sass::Script::Value::String)
      val.to_s
    end.join
  end

  def run_interp(text)
    run_interp_no_strip(text).strip
  end

  def handle_import_loop!(node)
    msg = "An @import loop has been found:"
    files = @environment.stack.frames.select {|f| f.is_import?}.map {|f| f.filename}.compact
    if node.filename == node.imported_file.options[:filename]
      raise Sass::SyntaxError.new("#{msg} #{node.filename} imports itself")
    end

    files << node.filename << node.imported_file.options[:filename]
    msg << "\n" << Sass::Util.enum_cons(files, 2).map do |m1, m2|
      "    #{m1} imports #{m2}"
    end.join("\n")
    raise Sass::SyntaxError.new(msg)
  end
  def visit_path(node)
    @immutable_path = {} if @immutable_path.nil?
    get_path(node)
  end
 
  def get_path(node)
    raw_path = run_interp(node.value)
    cleaned_path = clean_path(raw_path)
    puts cleaned_path
    cleaned_path = JSON.parse(cleaned_path);
 
    cleaned_path.each do |old_path, new_path|
      @immutable_path[old_path] = new_path
    end
  end
 
  def clean_path(path)
    parsed_path = path[6..-1]
    parsed_path.gsub!(/\A'|'\Z/, '')
    parsed_path.gsub!("(", "{")
    parsed_path.gsub!(")", "}")
    return parsed_path
  end
end