<===> input.scss
@warn "\"foo\"" + "";
@warn "" + "\"foo\"";
@warn "" + "\"foo";
@warn "\"foo\"" + "bar";
@warn unquote("\"foo\" and \"bar\"");

<===> output.css
<===> warning
WARNING: "foo"
         on line 7 of /sass/spec/libsass-issues/issue_2156/input.scss

WARNING: "foo"
         on line 8 of /sass/spec/libsass-issues/issue_2156/input.scss

WARNING: "foo
         on line 9 of /sass/spec/libsass-issues/issue_2156/input.scss

WARNING: "foo"bar
         on line 10 of /sass/spec/libsass-issues/issue_2156/input.scss

WARNING: "foo" and "bar"
         on line 11 of /sass/spec/libsass-issues/issue_2156/input.scss

<===> warning-dart-sass
WARNING: "foo"
    input.scss 1:1  root stylesheet

WARNING: "foo"
    input.scss 2:1  root stylesheet

WARNING: "foo
    input.scss 3:1  root stylesheet

WARNING: "foo"bar
    input.scss 4:1  root stylesheet

WARNING: "foo" and "bar"
    input.scss 5:1  root stylesheet