"IfStmt" is too specific, this needs to be anywhere that curlies are optional:

`for ( ...; ...; ... ) let a = 1; // illegal`
`for ( ... in ... ) let a = 1; // illegal`
`for ( ... of ... ) let a = 1; // illegal`
`while ( ... ) let a = 1; // illegal`
`else if ( ... ) let a = 1; // illegal`
`else let a = 1; // illegal`
`if (false) let a = 1; else if (true) let a = 1; else let a = 2; // illegal`