rollup merge of #19980: erickt/cleanup-serialize

This brings over some changes from [rustc-serialize](https://github.com/rust-lang/rustc-serialize). It makes sense to keep the two in sync until we finally remove libserialize, just to make sure they don't diverge from each other.

src/libserialize/json.rs

@@ -2012,7 +2012,6 @@ macro_rules! read_primitive {
 
 impl ::Decoder<DecoderError> for Decoder {
     fn read_nil(&mut self) -> DecodeResult<()> {
-        debug!("read_nil");
         expect!(self.pop(), Null)
     }
 
@@ -2030,7 +2029,6 @@ impl ::Decoder<DecoderError> for Decoder {
     fn read_f32(&mut self) -> DecodeResult<f32> { self.read_f64().map(|x| x as f32) }
 
     fn read_f64(&mut self) -> DecodeResult<f64> {
-        debug!("read_f64");
         match self.pop() {
             Json::I64(f) => Ok(f as f64),
             Json::U64(f) => Ok(f as f64),
@@ -2049,7 +2047,6 @@ impl ::Decoder<DecoderError> for Decoder {
     }
 
     fn read_bool(&mut self) -> DecodeResult<bool> {
-        debug!("read_bool");
         expect!(self.pop(), Boolean)
     }
 
@@ -2067,14 +2064,12 @@ impl ::Decoder<DecoderError> for Decoder {
     }
 
     fn read_str(&mut self) -> DecodeResult<string::String> {
-        debug!("read_str");
         expect!(self.pop(), String)
     }
 
-    fn read_enum<T, F>(&mut self, name: &str, f: F) -> DecodeResult<T> where
+    fn read_enum<T, F>(&mut self, _name: &str, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_enum({})", name);
         f(self)
     }
 
@@ -2082,7 +2077,6 @@ impl ::Decoder<DecoderError> for Decoder {
                                mut f: F) -> DecodeResult<T>
         where F: FnMut(&mut Decoder, uint) -> DecodeResult<T>,
     {
-        debug!("read_enum_variant(names={})", names);
         let name = match self.pop() {
             Json::String(s) => s,
             Json::Object(mut o) => {
@@ -2122,36 +2116,32 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, idx)
     }
 
-    fn read_enum_variant_arg<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+    fn read_enum_variant_arg<T, F>(&mut self, _idx: uint, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_enum_variant_arg(idx={})", idx);
         f(self)
     }
 
     fn read_enum_struct_variant<T, F>(&mut self, names: &[&str], f: F) -> DecodeResult<T> where
         F: FnMut(&mut Decoder, uint) -> DecodeResult<T>,
     {
-        debug!("read_enum_struct_variant(names={})", names);
         self.read_enum_variant(names, f)
     }
 
 
     fn read_enum_struct_variant_field<T, F>(&mut self,
-                                         name: &str,
+                                         _name: &str,
                                          idx: uint,
                                          f: F)
                                          -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_enum_struct_variant_field(name={}, idx={})", name, idx);
         self.read_enum_variant_arg(idx, f)
     }
 
-    fn read_struct<T, F>(&mut self, name: &str, len: uint, f: F) -> DecodeResult<T> where
+    fn read_struct<T, F>(&mut self, _name: &str, _len: uint, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_struct(name={}, len={})", name, len);
         let value = try!(f(self));
         self.pop();
         Ok(value)
@@ -2159,12 +2149,11 @@ impl ::Decoder<DecoderError> for Decoder {
 
     fn read_struct_field<T, F>(&mut self,
                                name: &str,
-                               idx: uint,
+                               _idx: uint,
                                f: F)
                                -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_struct_field(name={}, idx={})", name, idx);
         let mut obj = try!(expect!(self.pop(), Object));
 
         let value = match obj.remove(&name.to_string()) {
@@ -2189,7 +2178,6 @@ impl ::Decoder<DecoderError> for Decoder {
     fn read_tuple<T, F>(&mut self, tuple_len: uint, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_tuple()");
         self.read_seq(move |d, len| {
             if len == tuple_len {
                 f(d)
@@ -2202,18 +2190,16 @@ impl ::Decoder<DecoderError> for Decoder {
     fn read_tuple_arg<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_tuple_arg(idx={})", idx);
         self.read_seq_elt(idx, f)
     }
 
     fn read_tuple_struct<T, F>(&mut self,
-                               name: &str,
+                               _name: &str,
                                len: uint,
                                f: F)
                                -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_tuple_struct(name={})", name);
         self.read_tuple(len, f)
     }
 
@@ -2223,14 +2209,12 @@ impl ::Decoder<DecoderError> for Decoder {
                                    -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_tuple_struct_arg(idx={})", idx);
         self.read_tuple_arg(idx, f)
     }
 
     fn read_option<T, F>(&mut self, mut f: F) -> DecodeResult<T> where
         F: FnMut(&mut Decoder, bool) -> DecodeResult<T>,
     {
-        debug!("read_option()");
         match self.pop() {
             Json::Null => f(self, false),
             value => { self.stack.push(value); f(self, true) }
@@ -2240,7 +2224,6 @@ impl ::Decoder<DecoderError> for Decoder {
     fn read_seq<T, F>(&mut self, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
     {
-        debug!("read_seq()");
         let array = try!(expect!(self.pop(), Array));
         let len = array.len();
         for v in array.into_iter().rev() {
@@ -2249,17 +2232,15 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, len)
     }
 
-    fn read_seq_elt<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+    fn read_seq_elt<T, F>(&mut self, _idx: uint, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_seq_elt(idx={})", idx);
         f(self)
     }
 
     fn read_map<T, F>(&mut self, f: F) -> DecodeResult<T> where
         F: FnOnce(&mut Decoder, uint) -> DecodeResult<T>,
     {
-        debug!("read_map()");
         let obj = try!(expect!(self.pop(), Object));
         let len = obj.len();
         for (key, value) in obj.into_iter() {
@@ -2269,17 +2250,15 @@ impl ::Decoder<DecoderError> for Decoder {
         f(self, len)
     }
 
-    fn read_map_elt_key<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+    fn read_map_elt_key<T, F>(&mut self, _idx: uint, f: F) -> DecodeResult<T> where
        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_map_elt_key(idx={})", idx);
         f(self)
     }
 
-    fn read_map_elt_val<T, F>(&mut self, idx: uint, f: F) -> DecodeResult<T> where
+    fn read_map_elt_val<T, F>(&mut self, _idx: uint, f: F) -> DecodeResult<T> where
        F: FnOnce(&mut Decoder) -> DecodeResult<T>,
     {
-        debug!("read_map_elt_val(idx={})", idx);
         f(self)
     }
 
@@ -2441,9 +2420,7 @@ mod tests {
     use super::ParserError::*;
     use super::DecoderError::*;
     use super::JsonEvent::*;
-    use super::ParserState::*;
     use super::StackElement::*;
-    use super::InternalStackElement::*;
     use super::{PrettyEncoder, Json, from_str, DecodeResult, DecoderError, JsonEvent, Parser,
                 StackElement, Stack, Encoder, Decoder};
     use std::{i64, u64, f32, f64, io};
@@ -2678,8 +2655,6 @@ mod tests {
     }
 
     fn with_str_writer<F>(f: F) -> string::String where F: FnOnce(&mut io::Writer){
-        use std::str;
-
         let mut m = Vec::new();
         f(&mut m as &mut io::Writer);
         string::String::from_utf8(m).unwrap()