Rust: Creating a ExtCtxt for quasiquote outside of a syntax extension

test_extctxt.rs

#![feature(quote)]

extern crate syntax;

use syntax::print::pprust;
use syntax::codemap::DUMMY_SP;

fn main() {
	with_fake_extctxt(|cx| {
		let x = quote_expr!(cx, (a+b));
		let e = quote_expr!(cx, 2*$x+c);

		println!("{}", pprust::expr_to_str(e));
	});
}

fn with_fake_extctxt<T>(f: |&syntax::ext::base::ExtCtxt| -> T) -> T {
	let ps = syntax::parse::new_parse_sess();

	let mut cx = syntax::ext::base::ExtCtxt::new(&ps, Vec::new(), syntax::ext::expand::ExpansionConfig {
		deriving_hash_type_parameter: false,
		crate_id: from_str("test").unwrap(),
	});

	cx.bt_push(syntax::codemap::ExpnInfo{
		call_site: DUMMY_SP,
		callee: syntax::codemap::NameAndSpan {
			name: "test".to_string(),
			format: syntax::codemap::MacroBang,
			span: None,
		}
	});

	f(&cx)
}