Generated by SassMeister.com.

input.scss

@function add($value1, $value2, $return-calc: true) {
  @if $value1 == null {
    @return $value2;
  }

  @if $value2 == null {
    @return $value1;
  }
    
  @if type-of($value1) == number and type-of($value2) == number and comparable($value1, $value2) {
    @return $value1 + $value2;
  }
  
  @if type-of($value1) != number {
    $value1:  unquote("(") + $value1 + unquote(")");
  } 
  
  @if type-of($value2) != number {
    $value2:  unquote("(") + $value2 + unquote(")");
  }
  
  @if $return-calc == true {
    @return calc(#{$value1} + #{$value2});
  }

  @return $value1 + unquote(" + ") + $value2;
}

$value: add(1rem, 1em, false);

a {
    font-size: add(1vw, $value);
    type: type-of($value);
}

b {
    font-size: add(1rem, 1em);
}

output.css

a {
  font-size: calc(1vw + (1rem + 1em));
  type: string;
}

b {
  font-size: calc(1rem + 1em);
}

settings.json

{
  "sass": {
    "compiler": "dart-sass/1.32.12",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}