Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

// Our project defines some themes
$themes: (
  foo: (
    foreground: #5b5b5b,
    background: #f3f3f3
  )
);

// Our library also defines some themes
$libraryThemes: (
  foo: (
    foreground: #ccc,
    background: #3b3b3b
  ),
  bar: (
    foreground: #ccc,
    background: #3b3b3b
  ),
);

// Our library checks to see if there any priority themes to use
@if (variable-exists(themes)) {
  // if some exist, merge with the library giving the project themes priority
  $themes: map-merge($libraryThemes, $themes);
} @else {
  // if there aren't, just use the library themes
  $themes: $libraryThemes;
}

// Now, how do we automate the production of themes in a centralised file?

$themeMixins: ()!default;

@mixin button-theme($name) {
  $theme: map-get($themes, $name);
  
  .btn-t-#{$name} {
    color: map-get($theme, foreground);
    background-color: map-get($theme, background);
  }
}

// add this mixin to our list
$themeMixins: append($themeMixins, button-theme);

@each $mixin in $themeMixins {
  @each $name in map-keys($themes) {
    test: call($mixin, $name);
    .debug { 
      mixin: inspect($mixin);
      theme: inspect($name);
    }
  }
}

.debug{
  themes: inspect($themeMixins);
}

SassMeister-output.css

test: button-theme(foo);
.debug {
  mixin: button-theme;
  theme: foo;
}

test: button-theme(bar);
.debug {
  mixin: button-theme;
  theme: bar;
}

.debug {
  themes: button-theme;
}