expected_one_set_type_arguments

Set literals require one type argument or none, but {0} were found.

The analyzer produces this diagnostic when a set literal has more than one type argument.

The following code produces this diagnostic because the set literal has three type arguments when it can have at most one:

var s = <int, String, int>{0, 'a', 1};

Remove all except one of the type arguments:

var s = <int>{0, 1};