Generated by SassMeister.com.

SassMeister-input-HTML.html

<p class="qualifyClassname-p">
  Hello. I am a p tag;
</p>

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

@function first-char($str) { @return str-slice($str, 1, 1); }

@function remove-first-char($str) { @return str-slice($str, 2, str-length($str)); }

@function has-prefix-selector($str) {
  $prefix-selectors: ".", "#";
  @return index($prefix-selectors, first-char($str));
}

@function unprefix-parent($str) {
  @if has-prefix-selector($str) { $str: remove-first-char($str); }
  @return $str;
}

@mixin qualify($selector) { @at-root #{$selector + &} { @content; } }

@mixin true-qualify($type, $name) {
  $selector: $type + $name + unprefix-parent(#{&});
  @at-root #{$selector} { @content; }
}

$prefix: 'login-';

$class: '.';
$class-prefix: $class + $prefix;

$id: '#';
$id-prefix: $id + $prefix;

@mixin tq($type, $selector) { $parent: #{&};
  // color: gray;
  @include true-qualify($type, $selector) { context: $parent; }

  p { $parent: #{&};
    // color: green;
    @include true-qualify($type, $selector) { context: $parent; }

    .div { $parent: #{&};
      // color: red;
      @include true-qualify($type, $selector) { context: $parent; }
    }
  }
}

@mixin q($selector) { $parent: #{&};
  // color: black;
  @include qualify($selector) { context: $parent; }

  p { $parent: #{&};
    // color: blue;
    @include qualify($selector) { context: $parent; }

    .div { $parent: #{&};
      // color: yellow;
      @include qualify($selector) { context: $parent; }
    }
  }
}

nav {
  @include tq($class, $prefix);
  @include tq($id, $prefix);
  
  @include q($class-prefix); 
  @include q($id-prefix); 
}

.true-qualify { @include tq($class, $prefix); }
.qualify      { @include q($class-prefix); }

#true-qualify { @include tq($id, $prefix);  }
#qualify      { @include q($id-prefix); }

SassMeister-output.css

.login-nav { context: nav; }
.login-nav p { context: nav p; }
.login-nav p .div { context: nav p .div; }
#login-nav { context: nav; }
#login-nav p { context: nav p; }
#login-nav p .div { context: nav p .div; }
.login-nav { context: nav; }
.login-nav p { context: nav p; }
.login-nav p .div { context: nav p .div; }
#login-nav { context: nav; }
#login-nav p { context: nav p; }
#login-nav p .div { context: nav p .div; }

.login-true-qualify { context: .true-qualify; }
.login-true-qualify p { context: .true-qualify p; }
.login-true-qualify p .div { context: .true-qualify p .div; }

.login-.qualify { context: .qualify; }
.login-.qualify p { context: .qualify p; }
.login-.qualify p .div { context: .qualify p .div; }

#login-true-qualify { context: #true-qualify; }
#login-true-qualify p { context: #true-qualify p; }
#login-true-qualify p .div { context: #true-qualify p .div; }

#login-#qualify { context: #qualify; }
#login-#qualify p { context: #qualify p; }
#login-#qualify p .div { context: #qualify p .div; }

SassMeister-rendered.html

<p class="qualifyClassname-p">
  Hello. I am a p tag;
</p>