<===> input.scss
@function foo($arg2) {
  @return type-of($arg2);
}

@function foo_($arg2...) {
  @return type-of($arg2);
}

@function bar($arg1, $arg2) {
  @return type-of($arg1) + "::" + type-of($arg2);
}

@function bar_($arg1, $arg2...) {
  @return type-of($arg1) + "::" + type-of($arg2);
}

foo {
  foo: foo(one);
  foo: foo(one...);
  bar: bar(one, two);
  bar: bar(one, two...);
  foo: call('foo', one);
  foo: call('foo', one...);
  bar: call('bar', one, two);
  bar: call('bar', one, two...);
}

bar {
  foo: foo_(one);
  foo: foo_(one...);
  bar: bar_(one, two);
  bar: bar_(one, two...);
  foo: call('foo_', one);
  foo: call('foo_', one...);
  bar: call('bar_', one, two);
  bar: call('bar_', one, two...);
}
<===> output.css
foo {
  foo: string;
  foo: string;
  bar: string::string;
  bar: string::string;
  foo: string;
  foo: string;
  bar: string::string;
  bar: string::string;
}

bar {
  foo: arglist;
  foo: arglist;
  bar: string::arglist;
  bar: string::arglist;
  foo: arglist;
  foo: arglist;
  bar: string::arglist;
  bar: string::arglist;
}

<===> warning
DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(foo)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(foo)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(bar)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(bar)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(foo_)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(foo_)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(bar_)) instead.

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Sass 4.0. Use call(function-reference(bar_)) instead.

<===> warning-dart-sass
DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("foo")) instead.

   ,
22 |   foo: call('foo', one);
   |        ^^^^^^^^^^^^^^^^
   '
    input.scss 22:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("foo")) instead.

   ,
23 |   foo: call('foo', one...);
   |        ^^^^^^^^^^^^^^^^^^^
   '
    input.scss 23:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("bar")) instead.

   ,
24 |   bar: call('bar', one, two);
   |        ^^^^^^^^^^^^^^^^^^^^^
   '
    input.scss 24:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("bar")) instead.

   ,
25 |   bar: call('bar', one, two...);
   |        ^^^^^^^^^^^^^^^^^^^^^^^^
   '
    input.scss 25:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("foo_")) instead.

   ,
33 |   foo: call('foo_', one);
   |        ^^^^^^^^^^^^^^^^^
   '
    input.scss 33:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("foo_")) instead.

   ,
34 |   foo: call('foo_', one...);
   |        ^^^^^^^^^^^^^^^^^^^^
   '
    input.scss 34:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("bar_")) instead.

   ,
35 |   bar: call('bar_', one, two);
   |        ^^^^^^^^^^^^^^^^^^^^^^
   '
    input.scss 35:8  root stylesheet

DEPRECATION WARNING: Passing a string to call() is deprecated and will be illegal
in Dart Sass 2.0.0. Use call(get-function("bar_")) instead.

   ,
36 |   bar: call('bar_', one, two...);
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^
   '
    input.scss 36:8  root stylesheet