BEM-style mixin produces invalid selectors

[vladcosorg]

BEM-style mixin produces invalid selectors when compiled with libsass 3.2.4, whereas ruby sass produces expected output.

source.sass

@import mixins/bem

+b(address)
  +e(headline)
    color: #bebebe
    +m(footer)
      display: none

  +m(footer)
    +e(headline)
      font-weight: bold

ruby sass:

.address__headline {
  color: #bebebe;
}

.address__headline--footer {
  display: none;
}

.address--footer .address__headline {
  font-weight: bold;
}

libsass:

.address .address__headline {
  color: #bebebe; 
}
.address .address__headline .address .address__headline--footer {
    display: none; 
}

.address .address--footer .address .address--footer address .address__headline {
  font-weight: bold; 
}

BEM mixin helper:

// mixin use  bem style coding
$elementSeparator: "__"
$modifierSeparator: "--"

@function selectorToString($selector)
  $selector: inspect($selector)
  //cast to string
  $selector: str-slice($selector, 2, -2)
  //remove bracket
  @return $selector

@function containsModifier($selector)
  $selector: selectorToString($selector)
  @if str-index($selector, $modifierSeparator)
    @return true
  @else
    @return false

@function getBlock($selector)
  $selector: selectorToString($selector)
  @if str-index($selector, $modifierSeparator)
    $modifierStart: str-index($selector, $modifierSeparator) - 1
    @return str-slice($selector, 0, $modifierStart)
  @else
    @return $selector

=b($block)
  .#{$block}
    @content

=e($element)
  $selector: &
  $block: getBlock($selector)
  @if containsModifier($selector)
    @at-root #{$selector}
      #{$block + $elementSeparator + $element}
        @content
  @else
    @at-root #{$selector + $elementSeparator + $element}
      @content


=m($modifier)
  @at-root
    #{&}#{$modifierSeparator + $modifier}
      @content

[xzyfer]

Duplicate #1210

[vladcosorg]

Having the parent ticket marked as fixed, this specific case still does not work on latest beta.
Now the output is

.address__headline {
  color: #bebebe;
}

.address__headline--footer {
  display: none;
}

.address--footer address__headline {
  font-weight: bold;
}

Almost right, but notice the missing dot in the last selector.

[xzyfer]

@chetzof I've reduced this down to the core issue in #1583