class Sass::Selector::Sequence - sass-3.4.14 Documentation

# class Sass::Selector::Sequence

An operator-separated sequence of {SimpleSequence simple selector sequences}.

### Attributes

members[R]

The array of {SimpleSequence simple selector sequences}, operators, and newlines. The operators are strings such as `“+”` and `“>”` representing the corresponding CSS operators, or interpolated SassScript. Newlines are also newline strings; these aren't semantically relevant, but they do affect formatting.

@return [Array<SimpleSequence, String|Array<Sass::Tree::Node, String>>]

### Public Class Methods

new(seqs_and_ops) click to toggle source

@param seqs_and_ops [Array<SimpleSequence, String|Array<Sass::Tree::Node, String>>]

    See \{#members}

    # File lib/sass/selector/sequence.rb, line 38
    def initialize(seqs_and_ops)
      @members = seqs_and_ops
    end

### Public Instance Methods

add_sources!(sources) click to toggle source

Add to the {SimpleSequence#sources} sets of the child simple sequences. This destructively modifies this sequence's members array, but not the child simple sequences.

@param sources [Set<Sequence>]

    # File lib/sass/selector/sequence.rb, line 177
    def add_sources!(sources)
      members.map! {|m| m.is_a?(SimpleSequence) ? m.with_more_sources(sources) : m}
    end

contains_parent_ref?() click to toggle source

Returns whether there's a {Parent} selector anywhere in this sequence.

@return [Boolean]

    # File lib/sass/selector/sequence.rb, line 79
    def contains_parent_ref?
      members.any? do |sseq_or_op|
        next false unless sseq_or_op.is_a?(SimpleSequence)
        next true if sseq_or_op.members.first.is_a?(Parent)
        sseq_or_op.members.any? do |sel|
          sel.is_a?(Pseudo) && sel.selector && sel.selector.contains_parent_ref?
        end
      end
    end

do_extend(extends, parent_directives, replace, seen, original) click to toggle source

Non-destructively extends this selector with the extensions specified in a hash (which should come from {Sass::Tree::Visitors::Cssize}).

@param extends [Sass::Util::SubsetMap{Selector::Simple =>

                                        Sass::Tree::Visitors::Cssize::Extend}]
    The extensions to perform on this selector

@param parent_directives [Array<Sass::Tree::DirectiveNode>]

    The directives containing this selector.

@param replace [Boolean]

    Whether to replace the original selector entirely or include
    it in the result.

@param seen [Set<Array<Selector::Simple>>]

    The set of simple sequences that are currently being replaced.

@param original [Boolean]

    Whether this is the original selector being extended, as opposed to
    the result of a previous extension that's being re-extended.

@return [Array<Sequence>] A list of selectors generated

    by extending this selector with `extends`.
    These correspond to a {CommaSequence}'s {CommaSequence#members members array}.

@see Sass::Selector::CommaSequence#do_extend

    # File lib/sass/selector/sequence.rb, line 109
    def do_extend(extends, parent_directives, replace, seen, original)
      extended_not_expanded = members.map do |sseq_or_op|
        next [[sseq_or_op]] unless sseq_or_op.is_a?(SimpleSequence)
        extended = sseq_or_op.do_extend(extends, parent_directives, replace, seen)

        # The First Law of Extend says that the generated selector should have
        # specificity greater than or equal to that of the original selector.
        # In order to ensure that, we record the original selector's
        # (`extended.first`) original specificity.
        extended.first.add_sources!([self]) if original && !has_placeholder?

        extended.map {|seq| seq.members}
      end
      weaves = Sass::Util.paths(extended_not_expanded).map {|path| weave(path)}
      trim(weaves).map {|p| Sequence.new(p)}
    end

filename=(filename) click to toggle source

Sets the name of the file in which this selector was declared, or `nil` if it was not declared in a file (e.g. on stdin). This also sets the filename for all child selectors.

@param filename [String, nil] @return [String, nil]

    # File lib/sass/selector/sequence.rb, line 22
    def filename=(filename)
      members.each {|m| m.filename = filename if m.is_a?(SimpleSequence)}
      filename
    end

inspect() click to toggle source

Returns a string representation of the sequence. This is basically the selector string.

@return [String]

    # File lib/sass/selector/sequence.rb, line 168
    def inspect
      members.map {|m| m.inspect}.join(" ")
    end

line=(line) click to toggle source

Sets the line of the Sass template on which this selector was declared. This also sets the line for all child selectors.

@param line [Fixnum] @return [Fixnum]

    # File lib/sass/selector/sequence.rb, line 11
    def line=(line)
      members.each {|m| m.line = line if m.is_a?(SimpleSequence)}
      line
    end

resolve_parent_refs(super_cseq, implicit_parent) click to toggle source

Resolves the {Parent} selectors within this selector by replacing them with the given parent selector, handling commas appropriately.

@param super_cseq [CommaSequence] The parent selector @param implicit_parent [Boolean] Whether the the parent

    selector should automatically be prepended to the resolved
    selector if it contains no parent refs.

@return [CommaSequence] This selector, with parent references resolved @raise [Sass::SyntaxError] If a parent selector is invalid

    # File lib/sass/selector/sequence.rb, line 52
    def resolve_parent_refs(super_cseq, implicit_parent)
      members = @members.dup
      nl = (members.first == "\n" && members.shift)
      contains_parent_ref = contains_parent_ref?
      return CommaSequence.new([self]) if !implicit_parent && !contains_parent_ref

      unless contains_parent_ref
        old_members, members = members, []
        members << nl if nl
        members << SimpleSequence.new([Parent.new], false)
        members += old_members
      end

      CommaSequence.new(Sass::Util.paths(members.map do |sseq_or_op|
        next [sseq_or_op] unless sseq_or_op.is_a?(SimpleSequence)
        sseq_or_op.resolve_parent_refs(super_cseq).members
      end).map do |path|
        Sequence.new(path.map do |seq_or_op|
          next seq_or_op unless seq_or_op.is_a?(Sequence)
          seq_or_op.members
        end.flatten)
      end)
    end

subjectless() click to toggle source

Converts the subject operator “!”, if it exists, into a “:has()” selector.

@retur [Sequence]

    # File lib/sass/selector/sequence.rb, line 185
    def subjectless
      pre_subject = []
      has = []
      subject = nil
      members.each do |sseq_or_op|
        if subject
          has << sseq_or_op
        elsif sseq_or_op.is_a?(String) || !sseq_or_op.subject?
          pre_subject << sseq_or_op
        else
          subject = sseq_or_op.dup
          subject.members = sseq_or_op.members.dup
          subject.subject = false
          has = []
        end
      end

      return self unless subject

      unless has.empty?
        subject.members << Pseudo.new(:class, 'has', nil, CommaSequence.new([Sequence.new(has)]))
      end
      Sequence.new(pre_subject + [subject])
    end

superselector?(seq) click to toggle source

Returns whether or not this selector matches all elements that the given selector matches (as well as possibly more).

@example

    (.foo).superselector?(.foo.bar) #=> true
    (.foo).superselector?(.bar) #=> false

@param cseq [Sequence] @return [Boolean]

    # File lib/sass/selector/sequence.rb, line 155
    def superselector?(seq)
      _superselector?(members, seq.members)
    end

to_s() click to toggle source

@see Sass::Selector::AbstractSequence#to_s

    # File lib/sass/selector/sequence.rb, line 160
    def to_s
      @members.join(" ").gsub(/ ?\n ?/, "\n")
    end

unify(other) click to toggle source

Unifies this with another selector sequence to produce a selector that matches (a subset of) the intersection of the two inputs.

@param other [Sequence] @return [CommaSequence, nil] The unified selector, or nil if unification failed. @raise [Sass::SyntaxError] If this selector cannot be unified.

    This will only ever occur when a dynamic selector,
    such as {Parent} or {Interpolation}, is used in unification.
    Since these selectors should be resolved
    by the time extension and unification happen,
    this exception will only ever be raised as a result of programmer error

    # File lib/sass/selector/sequence.rb, line 137
    def unify(other)
      base = members.last
      other_base = other.members.last
      return unless base.is_a?(SimpleSequence) && other_base.is_a?(SimpleSequence)
      return unless (unified = other_base.unify(base))

      woven = weave([members[0...-1], other.members[0...-1] + [unified]])
      CommaSequence.new(woven.map {|w| Sequence.new(w)})
    end

### Private Instance Methods

_eql?(other) click to toggle source

    # File lib/sass/selector/sequence.rb, line 596
    def _eql?(other)
      other.members.reject {|m| m == "\n"}.eql?(members.reject {|m| m == "\n"})
    end

_hash() click to toggle source

    # File lib/sass/selector/sequence.rb, line 592
    def _hash
      members.reject {|m| m == "\n"}.hash
    end

_sources(seq) click to toggle source

    # File lib/sass/selector/sequence.rb, line 613
    def _sources(seq)
      s = Set.new
      seq.map {|sseq_or_op| s.merge sseq_or_op.sources if sseq_or_op.is_a?(SimpleSequence)}
      s
    end

_superselector?(seq1, seq2) click to toggle source

Given two selector sequences, returns whether `seq1` is a superselector of `seq2`; that is, whether `seq1` matches every element `seq2` matches.

@param seq1 [Array<SimpleSequence or String>] @param seq2 [Array<SimpleSequence or String>] @return [Boolean]

    # File lib/sass/selector/sequence.rb, line 486
    def _superselector?(seq1, seq2)
      seq1 = seq1.reject {|e| e == "\n"}
      seq2 = seq2.reject {|e| e == "\n"}
      # Selectors with leading or trailing operators are neither
      # superselectors nor subselectors.
      return if seq1.last.is_a?(String) || seq2.last.is_a?(String) ||
        seq1.first.is_a?(String) || seq2.first.is_a?(String)
      # More complex selectors are never superselectors of less complex ones
      return if seq1.size > seq2.size
      return seq1.first.superselector?(seq2.last, seq2[0...-1]) if seq1.size == 1

      _, si = Sass::Util.enum_with_index(seq2).find do |e, i|
        return if i == seq2.size - 1
        next if e.is_a?(String)
        seq1.first.superselector?(e, seq2[0...i])
      end
      return unless si

      if seq1[1].is_a?(String)
        return unless seq2[si + 1].is_a?(String)

        # .foo ~ .bar is a superselector of .foo + .bar
        return unless seq1[1] == "~" ? seq2[si + 1] != ">" : seq1[1] == seq2[si + 1]

        # .foo > .baz is not a superselector of .foo > .bar > .baz or .foo >
        # .bar .baz, despite the fact that .baz is a superselector of .bar >
        # .baz and .bar .baz. Same goes for + and ~.
        return if seq1.length == 3 && seq2.length > 3

        return _superselector?(seq1[2..-1], seq2[si + 2..-1])
      elsif seq2[si + 1].is_a?(String)
        return unless seq2[si + 1] == ">"
        return _superselector?(seq1[1..-1], seq2[si + 2..-1])
      else
        return _superselector?(seq1[1..-1], seq2[si + 1..-1])
      end
    end

chunks(seq1, seq2) { |seq1| ... } click to toggle source

Takes initial subsequences of `seq1` and `seq2` and returns all orderings of those subsequences. The initial subsequences are determined by a block.

Destructively removes the initial subsequences of `seq1` and `seq2`.

For example, given `(A B C | D E)` and `(1 2 | 3 4 5)` (with `|` denoting the boundary of the initial subsequence), this would return `[(A B C 1 2), (1 2 A B C)]`. The sequences would then be `(D E)` and `(3 4 5)`.

@param seq1 [Array] @param seq2 [Array] @yield [a] Used to determine when to cut off the initial subsequences.

    Called repeatedly for each sequence until it returns true.

@yieldparam a [Array] A final subsequence of one input sequence after

    cutting off some initial subsequence.

@yieldreturn [Boolean] Whether or not to cut off the initial subsequence

    here.

@return [Array<Array>] All possible orderings of the initial subsequences.

    # File lib/sass/selector/sequence.rb, line 446
    def chunks(seq1, seq2)
      chunk1 = []
      chunk1 << seq1.shift until yield seq1
      chunk2 = []
      chunk2 << seq2.shift until yield seq2
      return [] if chunk1.empty? && chunk2.empty?
      return [chunk2] if chunk1.empty?
      return [chunk1] if chunk2.empty?
      [chunk1 + chunk2, chunk2 + chunk1]
    end

extended_not_expanded_to_s(extended_not_expanded) click to toggle source

    # File lib/sass/selector/sequence.rb, line 619
    def extended_not_expanded_to_s(extended_not_expanded)
      extended_not_expanded.map do |choices|
        choices = choices.map do |sel|
          next sel.first.to_s if sel.size == 1
          "#{sel.join ' '}"
        end
        next choices.first if choices.size == 1 && !choices.include?(' ')
        "(#{choices.join ', '})"
      end.join ' '
    end

group_selectors(seq) click to toggle source

Groups a sequence into subsequences. The subsequences are determined by strings; adjacent non-string elements will be put into separate groups, but any element adjacent to a string will be grouped with that string.

For example, `(A B “C” D E “F” G “H” “I” J)` will become `[(A) (B “C” D) (E “F” G “H” “I” J)]`.

@param seq [Array] @return [Array<Array>]

    # File lib/sass/selector/sequence.rb, line 466
    def group_selectors(seq)
      newseq = []
      tail = seq.dup
      until tail.empty?
        head = []
        begin
          head << tail.shift
        end while !tail.empty? && head.last.is_a?(String) || tail.first.is_a?(String)
        newseq << head
      end
      newseq
    end

has_root?(sseq) click to toggle source

    # File lib/sass/selector/sequence.rb, line 630
    def has_root?(sseq)
      sseq.is_a?(SimpleSequence) &&
        sseq.members.any? {|sel| sel.is_a?(Pseudo) && sel.normalized_name == "root"}
    end

merge_final_ops(seq1, seq2, res = []) click to toggle source

Extracts final selector combinators (`“+”`, `“>”`, `“~”`) and the selectors to which they apply from two sequences and merges them together into a single array.

@param seq1 [Array<SimpleSequence or String>] @param seq2 [Array<SimpleSequence or String>] @return [Array<SimpleSequence or String or

      Array<Array<SimpleSequence or String>>]
    If there are no trailing combinators to be merged, this will be the
    empty array. If the trailing combinators cannot be merged, this will
    be nil. Otherwise, this will contained the merged selector. Array
    elements are [Sass::Util#paths]-style options; conceptually, an "or"
    of multiple selectors.

@comment

    rubocop:disable MethodLength

    # File lib/sass/selector/sequence.rb, line 342
    def merge_final_ops(seq1, seq2, res = [])
      ops1, ops2 = [], []
      ops1 << seq1.pop while seq1.last.is_a?(String)
      ops2 << seq2.pop while seq2.last.is_a?(String)

      # Not worth the headache of trying to preserve newlines here. The most
      # important use of newlines is at the beginning of the selector to wrap
      # across lines anyway.
      ops1.reject! {|o| o == "\n"}
      ops2.reject! {|o| o == "\n"}

      return res if ops1.empty? && ops2.empty?
      if ops1.size > 1 || ops2.size > 1
        # If there are multiple operators, something hacky's going on. If one
        # is a supersequence of the other, use that, otherwise give up.
        lcs = Sass::Util.lcs(ops1, ops2)
        return unless lcs == ops1 || lcs == ops2
        res.unshift(*(ops1.size > ops2.size ? ops1 : ops2).reverse)
        return res
      end

      # This code looks complicated, but it's actually just a bunch of special
      # cases for interactions between different combinators.
      op1, op2 = ops1.first, ops2.first
      if op1 && op2
        sel1 = seq1.pop
        sel2 = seq2.pop
        if op1 == '~' && op2 == '~'
          if sel1.superselector?(sel2)
            res.unshift sel2, '~'
          elsif sel2.superselector?(sel1)
            res.unshift sel1, '~'
          else
            merged = sel1.unify(sel2)
            res.unshift [
              [sel1, '~', sel2, '~'],
              [sel2, '~', sel1, '~'],
              ([merged, '~'] if merged)
            ].compact
          end
        elsif (op1 == '~' && op2 == '+') || (op1 == '+' && op2 == '~')
          if op1 == '~'
            tilde_sel, plus_sel = sel1, sel2
          else
            tilde_sel, plus_sel = sel2, sel1
          end

          if tilde_sel.superselector?(plus_sel)
            res.unshift plus_sel, '+'
          else
            merged = plus_sel.unify(tilde_sel)
            res.unshift [
              [tilde_sel, '~', plus_sel, '+'],
              ([merged, '+'] if merged)
            ].compact
          end
        elsif op1 == '>' && %w[~ +].include?(op2)
          res.unshift sel2, op2
          seq1.push sel1, op1
        elsif op2 == '>' && %w[~ +].include?(op1)
          res.unshift sel1, op1
          seq2.push sel2, op2
        elsif op1 == op2
          merged = sel1.unify(sel2)
          return unless merged
          res.unshift merged, op1
        else
          # Unknown selector combinators can't be unified
          return
        end
        return merge_final_ops(seq1, seq2, res)
      elsif op1
        seq2.pop if op1 == '>' && seq2.last && seq2.last.superselector?(seq1.last)
        res.unshift seq1.pop, op1
        return merge_final_ops(seq1, seq2, res)
      else # op2
        seq1.pop if op2 == '>' && seq1.last && seq1.last.superselector?(seq2.last)
        res.unshift seq2.pop, op2
        return merge_final_ops(seq1, seq2, res)
      end
    end

merge_initial_ops(seq1, seq2) click to toggle source

Extracts initial selector combinators (`“+”`, `“>”`, `“~”`, and `“n”`) from two sequences and merges them together into a single array of selector combinators.

@param seq1 [Array<SimpleSequence or String>] @param seq2 [Array<SimpleSequence or String>] @return [Array<String>, nil] If there are no operators in the merged

    sequence, this will be the empty array. If the operators cannot be
    merged, this will be nil.

    # File lib/sass/selector/sequence.rb, line 311
    def merge_initial_ops(seq1, seq2)
      ops1, ops2 = [], []
      ops1 << seq1.shift while seq1.first.is_a?(String)
      ops2 << seq2.shift while seq2.first.is_a?(String)

      newline = false
      newline ||= !!ops1.shift if ops1.first == "\n"
      newline ||= !!ops2.shift if ops2.first == "\n"

      # If neither sequence is a subsequence of the other, they cannot be
      # merged successfully
      lcs = Sass::Util.lcs(ops1, ops2)
      return unless lcs == ops1 || lcs == ops2
      (newline ? ["\n"] : []) + (ops1.size > ops2.size ? ops1 : ops2)
    end

parent_superselector?(seq1, seq2) click to toggle source

Like {#_superselector?}, but compares the selectors in the context of parent selectors, as though they shared an implicit base simple selector. For example, `B` is not normally a superselector of `B A`, since it doesn't match `A` elements. However, it is a parent superselector, since `B X` is a superselector of `B A X`.

@param seq1 [Array<SimpleSequence or String>] @param seq2 [Array<SimpleSequence or String>] @return [Boolean]

    # File lib/sass/selector/sequence.rb, line 534
    def parent_superselector?(seq1, seq2)
      base = Sass::Selector::SimpleSequence.new([Sass::Selector::Placeholder.new('<temp>')],
                                                false)
      _superselector?(seq1 + [base], seq2 + [base])
    end

path_has_two_subjects?(path) click to toggle source

    # File lib/sass/selector/sequence.rb, line 602
    def path_has_two_subjects?(path)
      subject = false
      path.each do |sseq_or_op|
        next unless sseq_or_op.is_a?(SimpleSequence)
        next unless sseq_or_op.subject?
        return true if subject
        subject = true
      end
      false
    end

subweave(seq1, seq2) click to toggle source

This interweaves two lists of selectors, returning all possible orderings of them (including using unification) that maintain the relative ordering of the input arrays.

For example, given `.foo .bar` and `.baz .bang`, this would return `.foo .bar .baz .bang`, `.foo .bar.baz .bang`, `.foo .baz .bar .bang`, `.foo .baz .bar.bang`, `.foo .baz .bang .bar`, and so on until `.baz .bang .foo .bar`.

Semantically, for selectors A and B, this returns all selectors `AB_i` such that the union over all i of elements matched by `AB_i X` is identical to the intersection of all elements matched by `A X` and all elements matched by `B X`. Some `AB_i` are elided to reduce the size of the output.

@param seq1 [Array<SimpleSequence or String>] @param seq2 [Array<SimpleSequence or String>] @return [Array<Array<SimpleSequence or String>>]

    # File lib/sass/selector/sequence.rb, line 258
    def subweave(seq1, seq2)
      return [seq2] if seq1.empty?
      return [seq1] if seq2.empty?

      seq1, seq2 = seq1.dup, seq2.dup
      return unless (init = merge_initial_ops(seq1, seq2))
      return unless (fin = merge_final_ops(seq1, seq2))

      # Make sure there's only one root selector in the output.
      root1 = has_root?(seq1.first) && seq1.shift
      root2 = has_root?(seq2.first) && seq2.shift
      if root1 && root2
        return unless (root = root1.unify(root2))
        seq1.unshift root
        seq2.unshift root
      elsif root1
        seq2.unshift root1
      elsif root2
        seq1.unshift root2
      end

      seq1 = group_selectors(seq1)
      seq2 = group_selectors(seq2)
      lcs = Sass::Util.lcs(seq2, seq1) do |s1, s2|
        next s1 if s1 == s2
        next unless s1.first.is_a?(SimpleSequence) && s2.first.is_a?(SimpleSequence)
        next s2 if parent_superselector?(s1, s2)
        next s1 if parent_superselector?(s2, s1)
      end

      diff = [[init]]

      until lcs.empty?
        diff << chunks(seq1, seq2) {|s| parent_superselector?(s.first, lcs.first)} << [lcs.shift]
        seq1.shift
        seq2.shift
      end
      diff << chunks(seq1, seq2) {|s| s.empty?}
      diff += fin.map {|sel| sel.is_a?(Array) ? sel : [sel]}
      diff.reject! {|c| c.empty?}

      Sass::Util.paths(diff).map {|p| p.flatten}.reject {|p| path_has_two_subjects?(p)}
    end

trim(seqses) click to toggle source

Removes redundant selectors from between multiple lists of selectors. This takes a list of lists of selector sequences; each individual list is assumed to have no redundancy within itself. A selector is only removed if it's redundant with a selector in another list.

“Redundant” here means that one selector is a superselector of the other. The more specific selector is removed.

@param seqses [Array<Array<Array<SimpleSequence or String>>>] @return [Array<Array<SimpleSequence or String>>]

    # File lib/sass/selector/sequence.rb, line 551
    def trim(seqses)
      # Avoid truly horrific quadratic behavior. TODO: I think there
      # may be a way to get perfect trimming without going quadratic.
      return Sass::Util.flatten(seqses, 1) if seqses.size > 100

      # Keep the results in a separate array so we can be sure we aren't
      # comparing against an already-trimmed selector. This ensures that two
      # identical selectors don't mutually trim one another.
      result = seqses.dup

      # This is n^2 on the sequences, but only comparing between
      # separate sequences should limit the quadratic behavior.
      seqses.each_with_index do |seqs1, i|
        result[i] = seqs1.reject do |seq1|
          # The maximum specificity of the sources that caused [seq1] to be
          # generated. In order for [seq1] to be removed, there must be
          # another selector that's a superselector of it *and* that has
          # specificity greater or equal to this.
          max_spec = _sources(seq1).map do |seq|
            spec = seq.specificity
            spec.is_a?(Range) ? spec.max : spec
          end.max || 0

          result.any? do |seqs2|
            next if seqs1.equal?(seqs2)
            # Second Law of Extend: the specificity of a generated selector
            # should never be less than the specificity of the extending
            # selector.
            #
            # See https://github.com/nex3/sass/issues/324.
            seqs2.any? do |seq2|
              spec2 = _specificity(seq2)
              spec2 = spec2.begin if spec2.is_a?(Range)
              spec2 >= max_spec && _superselector?(seq2, seq1)
            end
          end
        end
      end
      Sass::Util.flatten(result, 1)
    end

weave(path) click to toggle source

Conceptually, this expands “parenthesized selectors”. That is, if we have `.A .B {@extend .C}` and `.D .C {…}`, this conceptually expands into `.D .C, .D (.A .B)`, and this function translates `.D (.A .B)` into `.D .A .B, .A .D .B`. For thoroughness, `.A.D .B` would also be required, but including merged selectors results in exponential output for very little gain.

@param path [Array<Array<SimpleSequence or String>>]

    A list of parenthesized selector groups.

@return [Array<Array<SimpleSequence or String>>] A list of fully-expanded selectors.

    # File lib/sass/selector/sequence.rb, line 222
    def weave(path)
      # This function works by moving through the selector path left-to-right,
      # building all possible prefixes simultaneously.
      prefixes = [[]]

      path.each do |current|
        next if current.empty?
        current = current.dup
        last_current = [current.pop]
        prefixes = Sass::Util.flatten(prefixes.map do |prefix|
          sub = subweave(prefix, current)
          next [] unless sub
          sub.map {|seqs| seqs + last_current}
        end, 1)
      end
      prefixes
    end