path: root/actionpack/lib/action_view/template/error.rb

require "active_support/core_ext/enumerable"

module ActionView
  class Template
    # The Template::Error exception is raised when the compilation of the template fails. This exception then gathers a
    # bunch of intimate details and uses it to report a very precise exception message.
    class Error < ActionViewError #:nodoc:
      SOURCE_CODE_RADIUS = 3

      attr_reader :original_exception

      def initialize(template, assigns, original_exception)
        @template, @assigns, @original_exception = template, assigns.dup, original_exception
        @backtrace = compute_backtrace
      end

      def file_name
        @template.identifier
      end

      def message
        ActiveSupport::Deprecation.silence { original_exception.message }
      end

      def clean_backtrace
        if defined?(Rails) && Rails.respond_to?(:backtrace_cleaner)
          Rails.backtrace_cleaner.clean(original_exception.backtrace)
        else
          original_exception.backtrace
        end
      end

      def sub_template_message
        if @sub_templates
          "Trace of template inclusion: " +
          @sub_templates.collect { |template| template.inspect }.join(", ")
        else
          ""
        end
      end

      def source_extract(indentation = 0)
        return unless num = line_number
        num = num.to_i

        source_code = @template.source.split("\n")

        start_on_line = [ num - SOURCE_CODE_RADIUS - 1, 0 ].max
        end_on_line   = [ num + SOURCE_CODE_RADIUS - 1, source_code.length].min

        indent = ' ' * indentation
        line_counter = start_on_line
        return unless source_code = source_code[start_on_line..end_on_line]

        source_code.sum do |line|
          line_counter += 1
          "#{indent}#{line_counter}: #{line}\n"
        end
      end

      def sub_template_of(template_path)
        @sub_templates ||= []
        @sub_templates << template_path
      end

      def line_number
        @line_number ||=
          if file_name
            regexp = /#{Regexp.escape File.basename(file_name)}:(\d+)/

            $1 if message =~ regexp or clean_backtrace.find { |line| line =~ regexp }
          end
      end

      def to_s
        "\n#{self.class} (#{message}) #{source_location}:\n" + 
        "#{source_extract}\n    #{clean_backtrace.join("\n    ")}\n\n"
      end

      # don't do anything nontrivial here. Any raised exception from here becomes fatal 
      # (and can't be rescued).
      def backtrace
        @backtrace
      end

      private
        def compute_backtrace
          [
            "#{source_location.capitalize}\n\n#{source_extract(4)}\n    " +
            clean_backtrace.join("\n    ")
          ]
        end

        def source_location
          if line_number
            "on line ##{line_number} of "
          else
            'in '
          end + file_name
        end
    end
  end

  TemplateError = Template::Error
end