rollup merge of #21463: sanxiyn/demut

diff --cc src/libsyntax/parse/mod.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
index 865a71106964f0c2a04bb1390dcfd9cfcb636064,e538877edc8619d5f7aa2ff89d04b0c6de564ee6..2955ccb95ffd6a802fdb4dc0b04839bfcb6236a4
--- 1/src/libsyntax/parse/parser.rs
--- 2/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@@ -973,23 -973,23 +973,23 @@@ impl<'a> Parser<'a> 
          }
          return (4 - self.buffer_start) + self.buffer_end;
      }
 -    pub fn look_ahead<R, F>(&mut self, distance: uint, f: F) -> R where
 +    pub fn look_ahead<R, F>(&mut self, distance: usize, f: F) -> R where
          F: FnOnce(&token::Token) -> R,
      {
 -        let dist = distance as int;
 +        let dist = distance as isize;
          while self.buffer_length() < dist {
 -            self.buffer[self.buffer_end as uint] = self.reader.real_token();
 +            self.buffer[self.buffer_end as usize] = self.reader.real_token();
              self.buffer_end = (self.buffer_end + 1) & 3;
          }
 -        f(&self.buffer[((self.buffer_start + dist - 1) & 3) as uint].tok)
 +        f(&self.buffer[((self.buffer_start + dist - 1) & 3) as usize].tok)
      }
-     pub fn fatal(&mut self, m: &str) -> ! {
+     pub fn fatal(&self, m: &str) -> ! {
          self.sess.span_diagnostic.span_fatal(self.span, m)
      }
-     pub fn span_fatal(&mut self, sp: Span, m: &str) -> ! {
+     pub fn span_fatal(&self, sp: Span, m: &str) -> ! {
          self.sess.span_diagnostic.span_fatal(sp, m)
      }
-     pub fn span_fatal_help(&mut self, sp: Span, m: &str, help: &str) -> ! {
+     pub fn span_fatal_help(&self, sp: Span, m: &str, help: &str) -> ! {
          self.span_err(sp, m);
          self.span_help(sp, help);
          panic!(diagnostic::FatalError);