Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// ----

// First comments - whether the placeholder is added via a mixin, variable or function is 
// a red herring. It doesn't even have to be a placeholder - could be a normal selector.
// The problem is essentially to do with using @extend when you're not sure 
// if a part of the selector you're extending already targets the html element
// your new fragment of selector is supposed to target

//this approach doesn't work
%test1a {
  %placeholder-from-module1 {
    %test1b & {
        content: 'test1';
    }
  }
}

.test1a {
  @extend %test1a;
}

.test1b {
  @extend %test1b;
}

.test1 {
  .result1 {
    @extend %placeholder-from-module1;
  }
}

// this approach fixes the problem (although with an extraneous selector 
// due to nested selectors which could do with being tidied up)
%test2a {
  &%test2b %placeholder-from-module2 {
      content: 'test2';
  }
}

.test2a {
  @extend %test2a;
}

.test2b {
  @extend %test2b;
}

.test2 {
  .result2 {
    @extend %placeholder-from-module2;
  }
}


// this is broken again, and is the biggest worry because the point 
// where intermediate-wrapper and test3b are added could be in a different 
// module to where test3a is added so %test3b can't make any assumptions
// about whether it shoudl concatenate itself to existing selector fragments
%test3a {
  %placeholder-from-module3 {
    content: 'test3';
  }
}

%test3b .intermediate-wrapper {
  @extend %placeholder-from-module3;
}

.test3a {
  @extend %test3a;
}

.test3b {
  @extend %test3b;
}

.test3 {
  .result3 {
    @extend %placeholder-from-module3;
  }
}

SassMeister-output.css

.test1b .test1a .test1 .result1, .test1 .test1b .test1a .result1 {
  content: 'test1';
}

.test2a.test2b .test2 .result2, .test2 .test2a.test2b .result2 {
  content: 'test2';
}

.test3a .test3b .intermediate-wrapper, .test3b .test3a .intermediate-wrapper, .test3a .test3 .result3, .test3 .test3a .result3 {
  content: 'test3';
}