path: root/lib/error_highlight/base.rb

require_relative "version"

module ErrorHighlight
  # Identify the code fragment at that a given exception occurred.
  #
  # Options:
  #
  # point_type: :name | :args
  #   :name (default) points the method/variable name that the exception occurred.
  #   :args points the arguments of the method call that the exception occurred.
  #
  # backtrace_location: Thread::Backtrace::Location
  #   It locates the code fragment of the given backtrace_location.
  #   By default, it uses the first frame of backtrace_locations of the given exception.
  #
  # Returns:
  #  {
  #    first_lineno: Integer,
  #    first_column: Integer,
  #    last_lineno: Integer,
  #    last_column: Integer,
  #    snippet: String,
  #    script_lines: [String],
  #  } | nil
  #
  # Limitations:
  #
  # Currently, ErrorHighlight.spot only supports a single-line code fragment.
  # Therefore, if the return value is not nil, first_lineno and last_lineno will have
  # the same value. If the relevant code fragment spans multiple lines
  # (e.g., Array#[] of +ary[(newline)expr(newline)]+), the method will return nil.
  # This restriction may be removed in the future.
  def self.spot(obj, **opts)
    case obj
    when Exception
      exc = obj
      loc = opts[:backtrace_location]
      opts = { point_type: opts.fetch(:point_type, :name) }

      unless loc
        case exc
        when TypeError, ArgumentError
          opts[:point_type] = :args
        end

        locs = exc.backtrace_locations
        return nil unless locs

        loc = locs.first
        return nil unless loc

        opts[:name] = exc.name if NameError === obj
      end

      return nil unless Thread::Backtrace::Location === loc

      node =
        begin
          RubyVM::AbstractSyntaxTree.of(loc, keep_script_lines: true)
        rescue RuntimeError => error
          # RubyVM::AbstractSyntaxTree.of raises an error with a message that
          # includes "prism" when the ISEQ was compiled with the prism compiler.
          # In this case, we'll set the node to `nil`. In the future, we will
          # reparse with the prism parser and pass the parsed node to Spotter.
          raise unless error.message.include?("prism")
        end

      Spotter.new(node, **opts).spot

    when RubyVM::AbstractSyntaxTree::Node
      Spotter.new(obj, **opts).spot

    else
      raise TypeError, "Exception is expected"
    end

  rescue SyntaxError,
         SystemCallError, # file not found or something
         ArgumentError # eval'ed code

    return nil
  end

  class Spotter
    class NonAscii < Exception; end
    private_constant :NonAscii

    def initialize(node, point_type: :name, name: nil)
      @node = node
      @point_type = point_type
      @name = name

      # Not-implemented-yet options
      @arg = nil # Specify the index or keyword at which argument caused the TypeError/ArgumentError
      @multiline = false # Allow multiline spot

      @fetch = -> (lineno, last_lineno = lineno) do
        snippet = @node.script_lines[lineno - 1 .. last_lineno - 1].join("")
        snippet += "\n" unless snippet.end_with?("\n")

        # It require some work to support Unicode (or multibyte) characters.
        # Tentatively, we stop highlighting if the code snippet has non-ascii characters.
        # See https://github.com/ruby/error_highlight/issues/4
        raise NonAscii unless snippet.ascii_only?

        snippet
      end
    end

    OPT_GETCONSTANT_PATH = (RUBY_VERSION.split(".").map {|s| s.to_i } <=> [3, 2]) >= 0
    private_constant :OPT_GETCONSTANT_PATH

    def spot
      return nil unless @node

      if OPT_GETCONSTANT_PATH && @node.type == :COLON2
        # In Ruby 3.2 or later, a nested constant access (like `Foo::Bar::Baz`)
        # is compiled to one instruction (opt_getconstant_path).
        # @node points to the node of the whole `Foo::Bar::Baz` even if `Foo`
        # or `Foo::Bar` causes NameError.
        # So we try to spot the sub-node that causes the NameError by using
        # `NameError#name`.
        subnodes = []
        node = @node
        while node.type == :COLON2
          node2, const = node.children
          subnodes << node if const == @name
          node = node2
        end
        if node.type == :CONST || node.type == :COLON3
          if node.children.first == @name
            subnodes << node
          end

          # If we found only one sub-node whose name is equal to @name, use it
          return nil if subnodes.size != 1
          @node = subnodes.first
        else
          # Do nothing; opt_getconstant_path is used only when the const base is
          # NODE_CONST (`Foo`) or NODE_COLON3 (`::Foo`)
        end
      end

      case @node.type

      when :CALL, :QCALL
        case @point_type
        when :name
          spot_call_for_name
        when :args
          spot_call_for_args
        end

      when :ATTRASGN
        case @point_type
        when :name
          spot_attrasgn_for_name
        when :args
          spot_attrasgn_for_args
        end

      when :OPCALL
        case @point_type
        when :name
          spot_opcall_for_name
        when :args
          spot_opcall_for_args
        end

      when :FCALL
        case @point_type
        when :name
          spot_fcall_for_name
        when :args
          spot_fcall_for_args
        end

      when :VCALL
        spot_vcall

      when :OP_ASGN1
        case @point_type
        when :name
          spot_op_asgn1_for_name
        when :args
          spot_op_asgn1_for_args
        end

      when :OP_ASGN2
        case @point_type
        when :name
          spot_op_asgn2_for_name
        when :args
          spot_op_asgn2_for_args
        end

      when :CONST
        spot_vcall

      when :COLON2
        spot_colon2

      when :COLON3
        spot_vcall

      when :OP_CDECL
        spot_op_cdecl
      end

      if @snippet && @beg_column && @end_column && @beg_column < @end_column
        return {
          first_lineno: @beg_lineno,
          first_column: @beg_column,
          last_lineno: @end_lineno,
          last_column: @end_column,
          snippet: @snippet,
          script_lines: @node.script_lines,
        }
      else
        return nil
      end

    rescue NonAscii
      nil
    end

    private

    # Example:
    #   x.foo
    #    ^^^^
    #   x.foo(42)
    #    ^^^^
    #   x&.foo
    #    ^^^^^
    #   x[42]
    #    ^^^^
    #   x += 1
    #     ^
    def spot_call_for_name
      nd_recv, mid, nd_args = @node.children
      lineno = nd_recv.last_lineno
      lines = @fetch[lineno, @node.last_lineno]
      if mid == :[] && lines.match(/\G[\s)]*(\[(?:\s*\])?)/, nd_recv.last_column)
        @beg_column = $~.begin(1)
        @snippet = lines[/.*\n/]
        @beg_lineno = @end_lineno = lineno
        if nd_args
          if nd_recv.last_lineno == nd_args.last_lineno && @snippet.match(/\s*\]/, nd_args.last_column)
            @end_column = $~.end(0)
          end
        else
          if lines.match(/\G[\s)]*?\[\s*\]/, nd_recv.last_column)
            @end_column = $~.end(0)
          end
        end
      elsif lines.match(/\G[\s)]*?(\&?\.)(\s*?)(#{ Regexp.quote(mid) }).*\n/, nd_recv.last_column)
        lines = $` + $&
        @beg_column = $~.begin($2.include?("\n") ? 3 : 1)
        @end_column = $~.end(3)
        if i = lines[..@beg_column].rindex("\n")
          @beg_lineno = @end_lineno = lineno + lines[..@beg_column].count("\n")
          @snippet = lines[i + 1..]
          @beg_column -= i + 1
          @end_column -= i + 1
        else
          @snippet = lines
          @beg_lineno = @end_lineno = lineno
        end
      elsif mid.to_s =~ /\A\W+\z/ && lines.match(/\G\s*(#{ Regexp.quote(mid) })=.*\n/, nd_recv.last_column)
        @snippet = $` + $&
        @beg_column = $~.begin(1)
        @end_column = $~.end(1)
      end
    end

    # Example:
    #   x.foo(42)
    #         ^^
    #   x[42]
    #     ^^
    #   x += 1
    #        ^
    def spot_call_for_args
      _nd_recv, _mid, nd_args = @node.children
      if nd_args && nd_args.first_lineno == nd_args.last_lineno
        fetch_line(nd_args.first_lineno)
        @beg_column = nd_args.first_column
        @end_column = nd_args.last_column
      end
      # TODO: support @arg
    end

    # Example:
    #   x.foo = 1
    #    ^^^^^^
    #   x[42] = 1
    #    ^^^^^^
    def spot_attrasgn_for_name
      nd_recv, mid, nd_args = @node.children
      *nd_args, _nd_last_arg, _nil = nd_args.children
      fetch_line(nd_recv.last_lineno)
      if mid == :[]= && @snippet.match(/\G[\s)]*(\[)/, nd_recv.last_column)
        @beg_column = $~.begin(1)
        args_last_column = $~.end(0)
        if nd_args.last && nd_recv.last_lineno == nd_args.last.last_lineno
          args_last_column = nd_args.last.last_column
        end
        if @snippet.match(/[\s)]*\]\s*=/, args_last_column)
          @end_column = $~.end(0)
        end
      elsif @snippet.match(/\G[\s)]*(\.\s*#{ Regexp.quote(mid.to_s.sub(/=\z/, "")) }\s*=)/, nd_recv.last_column)
        @beg_column = $~.begin(1)
        @end_column = $~.end(1)
      end
    end

    # Example:
    #   x.foo = 1
    #           ^
    #   x[42] = 1
    #     ^^^^^^^
    #   x[] = 1
    #     ^^^^^
    def spot_attrasgn_for_args
      nd_recv, mid, nd_args = @node.children
      fetch_line(nd_recv.last_lineno)
      if mid == :[]= && @snippet.match(/\G[\s)]*\[/, nd_recv.last_column)
        @beg_column = $~.end(0)
        if nd_recv.last_lineno == nd_args.last_lineno
          @end_column = nd_args.last_column
        end
      elsif nd_args && nd_args.first_lineno == nd_args.last_lineno
        @beg_column = nd_args.first_column
        @end_column = nd_args.last_column
      end
      # TODO: support @arg
    end

    # Example:
    #   x + 1
    #     ^
    #   +x
    #   ^
    def spot_opcall_for_name
      nd_recv, op, nd_arg = @node.children
      fetch_line(nd_recv.last_lineno)
      if nd_arg
        # binary operator
        if @snippet.match(/\G[\s)]*(#{ Regexp.quote(op) })/, nd_recv.last_column)
          @beg_column = $~.begin(1)
          @end_column = $~.end(1)
        end
      else
        # unary operator
        if @snippet[...nd_recv.first_column].match(/(#{ Regexp.quote(op.to_s.sub(/@\z/, "")) })\s*\(?\s*\z/)
          @beg_column = $~.begin(1)
          @end_column = $~.end(1)
        end
      end
    end

    # Example:
    #   x + 1
    #       ^
    def spot_opcall_for_args
      _nd_recv, _op, nd_arg = @node.children
      if nd_arg && nd_arg.first_lineno == nd_arg.last_lineno
        # binary operator
        fetch_line(nd_arg.first_lineno)
        @beg_column = nd_arg.first_column
        @end_column = nd_arg.last_column
      end
    end

    # Example:
    #   foo(42)
    #   ^^^
    #   foo 42
    #   ^^^
    def spot_fcall_for_name
      mid, _nd_args = @node.children
      fetch_line(@node.first_lineno)
      if @snippet.match(/(#{ Regexp.quote(mid) })/, @node.first_column)
        @beg_column = $~.begin(1)
        @end_column = $~.end(1)
      end
    end

    # Example:
    #   foo(42)
    #       ^^
    #   foo 42
    #       ^^
    def spot_fcall_for_args
      _mid, nd_args = @node.children
      if nd_args && nd_args.first_lineno == nd_args.last_lineno
        # binary operator
        fetch_line(nd_args.first_lineno)
        @beg_column = nd_args.first_column
        @end_column = nd_args.last_column
      end
    end

    # Example:
    #   foo
    #   ^^^
    def spot_vcall
      if @node.first_lineno == @node.last_lineno
        fetch_line(@node.last_lineno)
        @beg_column = @node.first_column
        @end_column = @node.last_column
      end
    end

    # Example:
    #   x[1] += 42
    #    ^^^    (for [])
    #   x[1] += 42
    #        ^  (for +)
    #   x[1] += 42
    #    ^^^^^^ (for []=)
    def spot_op_asgn1_for_name
      nd_recv, op, nd_args, _nd_rhs = @node.children
      fetch_line(nd_recv.last_lineno)
      if @snippet.match(/\G[\s)]*(\[)/, nd_recv.last_column)
        bracket_beg_column = $~.begin(1)
        args_last_column = $~.end(0)
        if nd_args && nd_recv.last_lineno == nd_args.last_lineno
          args_last_column = nd_args.last_column
        end
        if @snippet.match(/\s*\](\s*)(#{ Regexp.quote(op) })=()/, args_last_column)
          case @name
          when :[], :[]=
            @beg_column = bracket_beg_column
            @end_column = $~.begin(@name == :[] ? 1 : 3)
          when op
            @beg_column = $~.begin(2)
            @end_column = $~.end(2)
          end
        end
      end
    end

    # Example:
    #   x[1] += 42
    #     ^^^^^^^^
    def spot_op_asgn1_for_args
      nd_recv, mid, nd_args, nd_rhs = @node.children
      fetch_line(nd_recv.last_lineno)
      if mid == :[]= && @snippet.match(/\G\s*\[/, nd_recv.last_column)
        @beg_column = $~.end(0)
        if nd_recv.last_lineno == nd_rhs.last_lineno
          @end_column = nd_rhs.last_column
        end
      elsif nd_args && nd_args.first_lineno == nd_rhs.last_lineno
        @beg_column = nd_args.first_column
        @end_column = nd_rhs.last_column
      end
      # TODO: support @arg
    end

    # Example:
    #   x.foo += 42
    #    ^^^     (for foo)
    #   x.foo += 42
    #         ^  (for +)
    #   x.foo += 42
    #    ^^^^^^^ (for foo=)
    def spot_op_asgn2_for_name
      nd_recv, _qcall, attr, op, _nd_rhs = @node.children
      fetch_line(nd_recv.last_lineno)
      if @snippet.match(/\G[\s)]*(\.)\s*#{ Regexp.quote(attr) }()\s*(#{ Regexp.quote(op) })(=)/, nd_recv.last_column)
        case @name
        when attr
          @beg_column = $~.begin(1)
          @end_column = $~.begin(2)
        when op
          @beg_column = $~.begin(3)
          @end_column = $~.end(3)
        when :"#{ attr }="
          @beg_column = $~.begin(1)
          @end_column = $~.end(4)
        end
      end
    end

    # Example:
    #   x.foo += 42
    #            ^^
    def spot_op_asgn2_for_args
      _nd_recv, _qcall, _attr, _op, nd_rhs = @node.children
      if nd_rhs.first_lineno == nd_rhs.last_lineno
        fetch_line(nd_rhs.first_lineno)
        @beg_column = nd_rhs.first_column
        @end_column = nd_rhs.last_column
      end
    end

    # Example:
    #   Foo::Bar
    #      ^^^^^
    def spot_colon2
      nd_parent, const = @node.children
      if nd_parent.last_lineno == @node.last_lineno
        fetch_line(nd_parent.last_lineno)
        @beg_column = nd_parent.last_column
        @end_column = @node.last_column
      else
        @snippet = @fetch[@node.last_lineno]
        if @snippet[...@node.last_column].match(/#{ Regexp.quote(const) }\z/)
          @beg_column = $~.begin(0)
          @end_column = $~.end(0)
        end
      end
    end

    # Example:
    #   Foo::Bar += 1
    #      ^^^^^^^^
    def spot_op_cdecl
      nd_lhs, op, _nd_rhs = @node.children
      *nd_parent_lhs, _const = nd_lhs.children
      if @name == op
        @snippet = @fetch[nd_lhs.last_lineno]
        if @snippet.match(/\G\s*(#{ Regexp.quote(op) })=/, nd_lhs.last_column)
          @beg_column = $~.begin(1)
          @end_column = $~.end(1)
        end
      else
        # constant access error
        @end_column = nd_lhs.last_column
        if nd_parent_lhs.empty? # example: ::C += 1
          if nd_lhs.first_lineno == nd_lhs.last_lineno
            @snippet = @fetch[nd_lhs.last_lineno]
            @beg_column = nd_lhs.first_column
          end
        else # example: Foo::Bar::C += 1
          if nd_parent_lhs.last.last_lineno == nd_lhs.last_lineno
            @snippet = @fetch[nd_lhs.last_lineno]
            @beg_column = nd_parent_lhs.last.last_column
          end
        end
      end
    end

    def fetch_line(lineno)
      @beg_lineno = @end_lineno = lineno
      @snippet = @fetch[lineno]
    end
  end

  private_constant :Spotter
end