Avoid cargo always re-compiling crates that use the syntax extension

The filename passed to new_parser_from_source_str gets added to the
codemap, which is used to generate the dep-info list, so cargo thought the
crate depended on a non-existent file called "peg". The dep-info output
ignores filenames surrounded by "<>".

It should probably instead somehow use the crate map entry for the
.rustpeg file, but that can wait for the new plugin API, if it applies
there.

Author: kevinmehall

src/rustast.rs

@@ -17,7 +17,7 @@ pub fn module(items: Vec<P<Item>>) -> P<Mod> {
 }
 
 pub fn parse_path(ctxt: &ExtCtxt, e: &str) -> ast::Path {
-	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "peg".to_string(), e.to_string());
+	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "<peg>".to_string(), e.to_string());
 	let r = panictry!(p.parse_path(syntax::parse::parser::NoTypesAllowed));
 	p.abort_if_errors();
 	r
@@ -28,14 +28,14 @@ pub fn parse_path_vec(s: &str) -> Vec<ast::Ident> {
 }
 
 pub fn parse_block(ctxt: &ExtCtxt, e: &str) -> P<ast::Block> {
-	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "peg".to_string(), e.to_string());
+	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "<peg>".to_string(), e.to_string());
 	let r = panictry!(p.parse_block());
 	p.abort_if_errors();
 	r
 }
 
 pub fn parse_type(ctxt: &ExtCtxt, e: &str) -> P<ast::Ty> {
-	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "peg".to_string(), e.to_string());
+	let mut p = syntax::parse::new_parser_from_source_str(&ctxt.parse_sess, Vec::new(), "<peg>".to_string(), e.to_string());
 	let r = panictry!(p.parse_ty());
 	p.abort_if_errors();
 	r