Class: JsDuck::Css::Lexer

Inherits:
Object
  • Object
show all
Defined in:
lib/jsduck/css/lexer.rb

Overview

Tokenizes CSS or SCSS code into lexical tokens.

Each token has a type and value. Types and possible values for them are as follows:

  • :number – “25.8”

  • :percentage – “25%”

  • :dimension – “2em”

  • :string – ‘“Hello world”’

  • :ident – “foo-bar”

  • :at_keyword – “@mixin”

  • :hash – “#00FF66”

  • :delim – “{”

  • :doc_comment – “/** My comment */”

Notice that doc-comments are recognized as tokens while normal comments are ignored just as whitespace.

Constant Summary collapse

IDENT =

Simplified token syntax based on: www.w3.org/TR/CSS21/syndata.html

/-?[_a-z][_a-z0-9-]*/i
NAME = 
/[_a-z0-9-]+/i
NUM = 
/[0-9]*\.[0-9]+|[0-9]+/

Instance Method Summary collapse

Constructor Details

#initialize(input) ⇒ Lexer

Initializes lexer with input string.



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# File 'lib/jsduck/css/lexer.rb', line 26

def initialize(input)
  @input = StringScanner.new(input)
  @buffer = []
end

Instance Method Details

#buffer_tokens(n) ⇒ Object

Ensures next n tokens are read in buffer

At the end of buffering the initial position scanpointer is restored. Only the #next method will advance the scanpointer in a way that’s visible outside this class.



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# File 'lib/jsduck/css/lexer.rb', line 84

def buffer_tokens(n)
  prev_pos = @input.pos
  @input.pos = @buffer.last[:pos] if @buffer.last
  (n - @buffer.length).times do
    @previous_token = tok = next_token
    if tok
      # remember scanpointer position after each token
      tok[:pos] = @input.pos
      @buffer << tok
    end
  end
  @input.pos = prev_pos
end

#empty? ⇒ Boolean

True when no more tokens.

Returns:

  • (Boolean) 


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# File 'lib/jsduck/css/lexer.rb', line 74

def empty?
  buffer_tokens(1)
  return !@buffer.first
end

#look(*tokens) ⇒ Object

Tests if given pattern matches the tokens that follow at current position.

Takes list of strings and symbols. Symbols are compared to token type, while strings to token value. For example:

look(:ident, ":", :dimension)



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# File 'lib/jsduck/css/lexer.rb', line 39

def look(*tokens)
  buffer_tokens(tokens.length)
  i = 0
  tokens.all? do |t|
    tok = @buffer[i]
    i += 1
    if !tok
      false
    elsif t.instance_of?(Symbol)
      tok[:type] == t
    else
      tok[:value] == t
    end
  end
end

#maybe(token_type, before_re, after_re) ⇒ Object

Returns token of given type when both regexes match. Otherwise returns :delim token with value of first regex match. First regex must always match.



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# File 'lib/jsduck/css/lexer.rb', line 175

def maybe(token_type, before_re, after_re)
  before = @input.scan(before_re)
  if @input.check(after_re)
    return {
      :type => token_type,
      :value => before + @input.scan(after_re)
    }
  else
    return {
      :type => :delim,
      :value => before
    }
  end
end

#next(full = false) ⇒ Object

Returns the value of next token, moving the current token cursor also to next token.

When full=true, returns full token as hash like so:

{:type => :ident, :value => "foo"}

For doc-comments the full token also contains the field :linenr, pointing to the line where the doc-comment began.



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# File 'lib/jsduck/css/lexer.rb', line 65

def next(full=false)
  buffer_tokens(1)
  tok = @buffer.shift
  # advance the scanpointer to the position after this token
  @input.pos = tok[:pos]
  full ? tok : tok[:value]
end

#next_token ⇒ Object

Parses out next token from input stream.



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# File 'lib/jsduck/css/lexer.rb', line 99

def next_token
  while !@input.eos? do
    skip_white
    if @input.check(IDENT)
      return {
        :type => :ident,
        :value => @input.scan(IDENT)
      }
    elsif @input.check(/'/)
      return {
        :type => :string,
        :value => @input.scan(/'([^'\\]|\\.)*('|\z)/m)
      }
    elsif @input.check(/"/)
      return {
        :type => :string,
        :value => @input.scan(/"([^"\\]|\\.)*("|\z)/m)
      }
    elsif @input.check(/\//)
      # Several things begin with dash:
      # - comments, regexes, division-operators
      if @input.check(/\/\*\*[^\/]/)
        return {
          :type => :doc_comment,
          # Calculate current line number, starting with 1
          :linenr => @input.string[0...@input.pos].count("\n") + 1,
          :value => @input.scan_until(/\*\/|\z/).sub(/\A\/\*\*/, "").sub(/\*\/\z/, "")
        }
      elsif @input.check(/\/\*/)
        # skip multiline comment
        @input.scan_until(/\*\/|\z/)
      elsif @input.check(/\/\//)
        # skip line comment
        @input.scan_until(/\n|\z/)
      else
        return {
          :type => :operator,
          :value => @input.scan(/\//)
        }
      end
    elsif @input.check(NUM)
      nr = @input.scan(NUM)
      if @input.check(/%/)
        return {
          :type => :percentage,
          :value => nr + @input.scan(/%/)
        }
      elsif @input.check(IDENT)
        return {
          :type => :dimension,
          :value => nr + @input.scan(IDENT)
        }
      else
        return {
          :type => :number,
          :value => nr
        }
      end
    elsif @input.check(/@/)
      return maybe(:at_keyword, /@/, IDENT)
    elsif @input.check(/#/)
      return maybe(:hash, /#/, NAME)
    elsif @input.check(/\$/)
      return maybe(:var, /\$/, IDENT)
    elsif @input.check(/./)
      return {
        :type => :delim,
        :value => @input.scan(/./)
      }
    end
  end
end

#skip_white ⇒ Object 



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# File 'lib/jsduck/css/lexer.rb', line 190

def skip_white
  @input.scan(/\s+/)
end