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 181
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 83
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 CommaSequence#do_extend

# File lib/sass/selector/sequence.rb, line 113
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 && !invisible?

    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 172
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 [Integer] @return [Integer]

# File lib/sass/selector/sequence.rb, line 11
def line=(line)
  members.each {|m| m.line = line if m.is_a?(SimpleSequence)}
  @line = 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|
    path_members = path.map do |seq_or_op|
      next seq_or_op unless seq_or_op.is_a?(Sequence)
      seq_or_op.members
    end
    if path_members.length == 2 && path_members[1][0] == "\n"
      path_members[0].unshift path_members[1].shift
    end
    Sequence.new(path_members.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 189
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 159
def superselector?(seq)
  _superselector?(members, seq.members)
end
to_s(opts = {}) click to toggle source

@see AbstractSequence#to_s

# File lib/sass/selector/sequence.rb, line 164
def to_s(opts = {})
  @members.map {|m| m.is_a?(String) ? m : m.to_s(opts)}.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 141
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 623
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 619
def _hash
  members.reject {|m| m == "\n"}.hash
end
_sources(seq) click to toggle source
# File lib/sass/selector/sequence.rb, line 638
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 489
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 = seq2.each_with_index.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 449
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 644
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 469
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 655
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.
# File lib/sass/selector/sequence.rb, line 347
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 318
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
must_unify?(seq1, seq2) click to toggle source

Returns whether two selectors must be unified to produce a valid combined selector. This is true when both selectors contain the same unique simple selector such as an id.

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

# File lib/sass/selector/sequence.rb, line 550
def must_unify?(seq1, seq2)
  unique_selectors = seq1.map do |sseq|
    next [] if sseq.is_a?(String)
    sseq.members.select {|sel| sel.unique?}
  end.flatten.to_set

  return false if unique_selectors.empty?

  seq2.any? do |sseq|
    next false if sseq.is_a?(String)
    sseq.members.any? do |sel|
      next unless sel.unique?
      unique_selectors.include?(sel)
    end
  end
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 537
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 627
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 262
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)
    next unless must_unify?(s1, s2)
    next unless (unified = Sequence.new(s1).unify(Sequence.new(s2)))
    unified.members.first.members if unified.members.length == 1
  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 578
def trim(seqses)
  # Avoid truly horrific quadratic behavior. TODO: I think there
  # may be a way to get perfect trimming without going quadratic.
  return seqses.flatten(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
  result.flatten(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 226
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 = prefixes.map do |prefix|
      sub = subweave(prefix, current)
      next [] unless sub
      sub.map {|seqs| seqs + last_current}
    end.flatten(1)
  end
  prefixes
end