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

<===> output.css
<===> warning
/sass/spec/libsass-issues/issue_2156/input.scss:1 DEBUG: "foo"
/sass/spec/libsass-issues/issue_2156/input.scss:2 DEBUG: "foo"
/sass/spec/libsass-issues/issue_2156/input.scss:3 DEBUG: "foo
/sass/spec/libsass-issues/issue_2156/input.scss:4 DEBUG: "foo"bar
/sass/spec/libsass-issues/issue_2156/input.scss:5 DEBUG: "foo" and "bar"