Compiler options have different effects on command line vs in fourslash test

TypeScript Version: Version 3.0.0-dev.20180616

Code

/// <reference path="fourslash.ts" />

// @target: esnext

////Symbol.iterator;

verify.noErrors();

This fourslash test fails. But putting Symbol.iterator; in a file and running tsc a.ts --target esnext compiles with no error. // @lib: esnext doesn't work either, even though tsc a.ts --lib esnext works.

@rbuckton This works for other options, it probably has something to do with #23893.

This isn't actually about compiler flags, the following compiles fine with no compile flags but fails as a fourslash test:

/// <reference lib="es2015" />
Symbol.iterator;