Fix the string literal parsing

Author: Zoxc

src/libsyntax/ext/tt/macro_parser.rs

@@ -586,7 +586,8 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
             }
         },
         "pat" => token::NtPat(panictry!(p.parse_pat())),
-        "expr" | "str" => token::NtExpr(panictry!(p.parse_expr())),
+        "str" => token::NtExpr(panictry!(p.parse_lit_as_expr())),
+        "expr" => token::NtExpr(panictry!(p.parse_expr())),
         "ty" => token::NtTy(panictry!(p.parse_ty())),
         // this could be handled like a token, since it is one
         "ident" => match p.token {

src/libsyntax/parse/parser.rs

@@ -1758,16 +1758,20 @@ impl<'a> Parser<'a> {
         Ok(codemap::Spanned { node: lit, span: lo.to(self.prev_span) })
     }
 
+    pub fn parse_lit_as_expr(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.span;
+        let literal = P(self.parse_lit()?);
+        let hi = self.prev_span;
+        Ok(self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new()))
+    }
+
     /// matches '-' lit | lit (cf. ast_validation::AstValidator::check_expr_within_pat)
     pub fn parse_pat_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
         maybe_whole_expr!(self);
 
         let minus_lo = self.span;
         let minus_present = self.eat(&token::BinOp(token::Minus));
-        let lo = self.span;
-        let literal = P(self.parse_lit()?);
-        let hi = self.prev_span;
-        let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
+        let expr = self.parse_lit_as_expr()?;
 
         if minus_present {
             let minus_hi = self.prev_span;