replace parse_lifetime with expect_lifetime

made `parser::Parser::expect_lifetime` public, so it can be called from `macro_parser::parse_nt`

Author: mikeyhew

src/libsyntax/ext/tt/macro_parser.rs

@@ -603,7 +603,7 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
         "path" => token::NtPath(panictry!(p.parse_path_common(PathStyle::Type, false))),
         "meta" => token::NtMeta(panictry!(p.parse_meta_item())),
         "vis" => token::NtVis(panictry!(p.parse_visibility(true))),
-        "lifetime" => token::NtLifetime(panictry!(p.parse_lifetime())),
+        "lifetime" => token::NtLifetime(p.expect_lifetime()),
         // this is not supposed to happen, since it has been checked
         // when compiling the macro.
         _ => p.span_bug(sp, "invalid fragment specifier")

src/libsyntax/parse/parser.rs

@@ -2031,7 +2031,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse single lifetime 'a or panic.
-    fn expect_lifetime(&mut self) -> Lifetime {
+    pub fn expect_lifetime(&mut self) -> Lifetime {
         match self.token {
             token::Lifetime(ident) => {
                 let ident_span = self.span;