json-encoder: report error when hash map key is not string or numeric

src/libserialize/json.rs

@@ -202,7 +202,7 @@ use self::InternalStackElement::*;
 use std;
 use std::collections::{HashMap, BTreeMap};
 use std::{char, f64, fmt, io, num, str};
-use std::mem::{swap, transmute};
+use std::mem::{swap};
 use std::num::{Float, Int};
 use std::num::FpCategory as Fp;
 use std::str::FromStr;
@@ -275,6 +275,12 @@ pub enum DecoderError {
     ApplicationError(string::String)
 }
 
+#[derive(Copy, Show)]
+pub enum EncoderError {
+    FmtError(fmt::Error),
+    BadHashmapKey,
+}
+
 /// Returns a readable error string for a given error code.
 pub fn error_str(error: ErrorCode) -> &'static str {
     match error {
@@ -334,10 +340,19 @@ impl std::error::Error for DecoderError {
     fn detail(&self) -> Option<std::string::String> { Some(format!("{:?}", self)) }
 }
 
-pub type EncodeResult = fmt::Result;
+impl std::error::Error for EncoderError {
+    fn description(&self) -> &str { "encoder error" }
+    fn detail(&self) -> Option<std::string::String> { Some(format!("{:?}", self)) }
+}
+
+impl std::error::FromError<fmt::Error> for EncoderError {
+    fn from_error(err: fmt::Error) -> EncoderError { EncoderError::FmtError(err) }
+}
+
+pub type EncodeResult = Result<(), EncoderError>;
 pub type DecodeResult<T> = Result<T, DecoderError>;
 
-fn escape_str(wr: &mut fmt::Writer, v: &str) -> fmt::Result {
+fn escape_str(wr: &mut fmt::Writer, v: &str) -> EncodeResult {
     try!(wr.write_str("\""));
 
     let mut start = 0;
@@ -395,17 +410,18 @@ fn escape_str(wr: &mut fmt::Writer, v: &str) -> fmt::Result {
         try!(wr.write_str(&v[start..]));
     }
 
-    wr.write_str("\"")
+    try!(wr.write_str("\""));
+    Ok(())
 }
 
-fn escape_char(writer: &mut fmt::Writer, v: char) -> fmt::Result {
+fn escape_char(writer: &mut fmt::Writer, v: char) -> EncodeResult {
     let mut buf = [0; 4];
     let n = v.encode_utf8(&mut buf).unwrap();
     let buf = unsafe { str::from_utf8_unchecked(&buf[..n]) };
     escape_str(writer, buf)
 }
 
-fn spaces(wr: &mut fmt::Writer, mut n: uint) -> fmt::Result {
+fn spaces(wr: &mut fmt::Writer, mut n: uint) -> EncodeResult {
     const BUF: &'static str = "                ";
 
     while n >= BUF.len() {
@@ -414,10 +430,9 @@ fn spaces(wr: &mut fmt::Writer, mut n: uint) -> fmt::Result {
     }
 
     if n > 0 {
-        wr.write_str(&BUF[..n])
+        try!(wr.write_str(&BUF[..n]));
-    } else {
-        Ok(())
     }
+    Ok(())
 }
 
 fn fmt_number_or_null(v: f64) -> string::String {
@@ -431,43 +446,62 @@ fn fmt_number_or_null(v: f64) -> string::String {
 /// A structure for implementing serialization to JSON.
 pub struct Encoder<'a> {
     writer: &'a mut (fmt::Writer+'a),
+    is_emitting_map_key: bool,
 }
 
 impl<'a> Encoder<'a> {
     /// Creates a new JSON encoder whose output will be written to the writer
     /// specified.
     pub fn new(writer: &'a mut fmt::Writer) -> Encoder<'a> {
-        Encoder { writer: writer }
+        Encoder { writer: writer, is_emitting_map_key: false, }
+    }
+}
+
+macro_rules! emit_enquoted_if_mapkey {
+    ($enc:ident,$e:expr) => {
+        if $enc.is_emitting_map_key {
+            try!(write!($enc.writer, "\"{}\"", $e));
+            Ok(())
+        } else {
+            try!(write!($enc.writer, "{}", $e));
+            Ok(())
+        }
     }
 }
 
 impl<'a> ::Encoder for Encoder<'a> {
-    type Error = fmt::Error;
+    type Error = EncoderError;
 
-    fn emit_nil(&mut self) -> EncodeResult { write!(self.writer, "null") }
+    fn emit_nil(&mut self) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
+        try!(write!(self.writer, "null"));
+        Ok(())
+    }
 
-    fn emit_uint(&mut self, v: uint) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_uint(&mut self, v: uint) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u64(&mut self, v: u64) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u64(&mut self, v: u64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u32(&mut self, v: u32) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u32(&mut self, v: u32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u16(&mut self, v: u16) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u16(&mut self, v: u16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u8(&mut self, v: u8) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u8(&mut self, v: u8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
 
-    fn emit_int(&mut self, v: int) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_int(&mut self, v: int) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i64(&mut self, v: i64) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i64(&mut self, v: i64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i32(&mut self, v: i32) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i32(&mut self, v: i32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i16(&mut self, v: i16) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i16(&mut self, v: i16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i8(&mut self, v: i8) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i8(&mut self, v: i8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
 
     fn emit_bool(&mut self, v: bool) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if v {
-            write!(self.writer, "true")
+            try!(write!(self.writer, "true"));
         } else {
-            write!(self.writer, "false")
+            try!(write!(self.writer, "false"));
         }
+        Ok(())
     }
 
     fn emit_f64(&mut self, v: f64) -> EncodeResult {
-        write!(self.writer, "{}", fmt_number_or_null(v))
+        emit_enquoted_if_mapkey!(self, fmt_number_or_null(v))
     }
     fn emit_f32(&mut self, v: f32) -> EncodeResult {
         self.emit_f64(v as f64)
@@ -483,6 +517,7 @@ impl<'a> ::Encoder for Encoder<'a> {
     fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
 
@@ -496,6 +531,7 @@ impl<'a> ::Encoder for Encoder<'a> {
         // enums are encoded as strings or objects
         // Bunny => "Bunny"
         // Kangaroo(34,"William") => {"variant": "Kangaroo", "fields": [34,"William"]}
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if cnt == 0 {
             escape_str(self.writer, name)
         } else {
@@ -503,13 +539,15 @@ impl<'a> ::Encoder for Encoder<'a> {
             try!(escape_str(self.writer, name));
             try!(write!(self.writer, ",\"fields\":["));
             try!(f(self));
-            write!(self.writer, "]}}")
+            try!(write!(self.writer, "]}}"));
+            Ok(())
         }
     }
 
     fn emit_enum_variant_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx != 0 {
             try!(write!(self.writer, ","));
         }
@@ -523,6 +561,7 @@ impl<'a> ::Encoder for Encoder<'a> {
                                    f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_enum_variant(name, id, cnt, f)
     }
 
@@ -532,20 +571,24 @@ impl<'a> ::Encoder for Encoder<'a> {
                                          f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_enum_variant_arg(idx, f)
     }
 
     fn emit_struct<F>(&mut self, _: &str, _: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         try!(write!(self.writer, "{{"));
         try!(f(self));
-        write!(self.writer, "}}")
+        try!(write!(self.writer, "}}"));
+        Ok(())
     }
 
     fn emit_struct_field<F>(&mut self, name: &str, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx != 0 { try!(write!(self.writer, ",")); }
         try!(escape_str(self.writer, name));
         try!(write!(self.writer, ":"));
@@ -555,48 +598,60 @@ impl<'a> ::Encoder for Encoder<'a> {
     fn emit_tuple<F>(&mut self, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq(len, f)
     }
     fn emit_tuple_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq_elt(idx, f)
     }
 
     fn emit_tuple_struct<F>(&mut self, _name: &str, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq(len, f)
     }
     fn emit_tuple_struct_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq_elt(idx, f)
     }
 
     fn emit_option<F>(&mut self, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
-    fn emit_option_none(&mut self) -> EncodeResult { self.emit_nil() }
+    fn emit_option_none(&mut self) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
+        self.emit_nil()
+    }
     fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
 
     fn emit_seq<F>(&mut self, _len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         try!(write!(self.writer, "["));
         try!(f(self));
-        write!(self.writer, "]")
+        try!(write!(self.writer, "]"));
+        Ok(())
     }
 
     fn emit_seq_elt<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx != 0 {
             try!(write!(self.writer, ","));
         }
@@ -606,34 +661,28 @@ impl<'a> ::Encoder for Encoder<'a> {
     fn emit_map<F>(&mut self, _len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         try!(write!(self.writer, "{{"));
         try!(f(self));
-        write!(self.writer, "}}")
+        try!(write!(self.writer, "}}"));
+        Ok(())
     }
 
     fn emit_map_elt_key<F>(&mut self, idx: uint, mut f: F) -> EncodeResult where
         F: FnMut(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx != 0 { try!(write!(self.writer, ",")) }
-        // ref #12967, make sure to wrap a key in double quotes,
+        self.is_emitting_map_key = true;
-        // in the event that its of a type that omits them (eg numbers)
-        let mut buf = Vec::new();
-        // FIXME(14302) remove the transmute and unsafe block.
-        unsafe {
-            let mut check_encoder = Encoder::new(&mut buf);
-            try!(f(transmute(&mut check_encoder)));
-        }
-        let out = str::from_utf8(&buf[]).unwrap();
-        let needs_wrapping = out.char_at(0) != '"' && out.char_at_reverse(out.len()) != '"';
-        if needs_wrapping { try!(write!(self.writer, "\"")); }
         try!(f(self));
-        if needs_wrapping { try!(write!(self.writer, "\"")); }
+        self.is_emitting_map_key = false;
         Ok(())
     }
 
     fn emit_map_elt_val<F>(&mut self, _idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut Encoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         try!(write!(self.writer, ":"));
         f(self)
     }
@@ -645,12 +694,18 @@ pub struct PrettyEncoder<'a> {
     writer: &'a mut (fmt::Writer+'a),
     curr_indent: uint,
     indent: uint,
+    is_emitting_map_key: bool,
 }
 
 impl<'a> PrettyEncoder<'a> {
     /// Creates a new encoder whose output will be written to the specified writer
     pub fn new(writer: &'a mut fmt::Writer) -> PrettyEncoder<'a> {
-        PrettyEncoder { writer: writer, curr_indent: 0, indent: 2, }
+        PrettyEncoder {
+            writer: writer,
+            curr_indent: 0,
+            indent: 2,
+            is_emitting_map_key: false,
+        }
     }
 
     /// Set the number of spaces to indent for each level.
@@ -664,32 +719,38 @@ impl<'a> PrettyEncoder<'a> {
 }
 
 impl<'a> ::Encoder for PrettyEncoder<'a> {
-    type Error = fmt::Error;
+    type Error = EncoderError;
 
-    fn emit_nil(&mut self) -> EncodeResult { write!(self.writer, "null") }
+    fn emit_nil(&mut self) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
+        try!(write!(self.writer, "null"));
+        Ok(())
+    }
 
-    fn emit_uint(&mut self, v: uint) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_uint(&mut self, v: uint) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u64(&mut self, v: u64) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u64(&mut self, v: u64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u32(&mut self, v: u32) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u32(&mut self, v: u32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u16(&mut self, v: u16) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u16(&mut self, v: u16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_u8(&mut self, v: u8) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_u8(&mut self, v: u8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
 
-    fn emit_int(&mut self, v: int) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_int(&mut self, v: int) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i64(&mut self, v: i64) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i64(&mut self, v: i64) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i32(&mut self, v: i32) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i32(&mut self, v: i32) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i16(&mut self, v: i16) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i16(&mut self, v: i16) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
-    fn emit_i8(&mut self, v: i8) -> EncodeResult { write!(self.writer, "{}", v) }
+    fn emit_i8(&mut self, v: i8) -> EncodeResult { emit_enquoted_if_mapkey!(self, v) }
 
     fn emit_bool(&mut self, v: bool) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if v {
-            write!(self.writer, "true")
+            try!(write!(self.writer, "true"));
         } else {
-            write!(self.writer, "false")
+            try!(write!(self.writer, "false"));
         }
+        Ok(())
     }
 
     fn emit_f64(&mut self, v: f64) -> EncodeResult {
-        write!(self.writer, "{}", fmt_number_or_null(v))
+        emit_enquoted_if_mapkey!(self, fmt_number_or_null(v))
     }
     fn emit_f32(&mut self, v: f32) -> EncodeResult {
         self.emit_f64(v as f64)
@@ -705,6 +766,7 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
     fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
 
@@ -716,6 +778,7 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
                             -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if cnt == 0 {
             escape_str(self.writer, name)
         } else {
@@ -735,13 +798,15 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
             self.curr_indent -= self.indent;
             try!(write!(self.writer, "]\n"));
             try!(spaces(self.writer, self.curr_indent));
-            write!(self.writer, "}}")
+            try!(write!(self.writer, "}}"));
+            Ok(())
         }
     }
 
     fn emit_enum_variant_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx != 0 {
             try!(write!(self.writer, ",\n"));
         }
@@ -756,6 +821,7 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
                                    f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_enum_variant(name, id, cnt, f)
     }
 
@@ -765,6 +831,7 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
                                          f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_enum_variant_arg(idx, f)
     }
 
@@ -772,8 +839,9 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
     fn emit_struct<F>(&mut self, _: &str, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if len == 0 {
-            write!(self.writer, "{{}}")
+            try!(write!(self.writer, "{{}}"));
         } else {
             try!(write!(self.writer, "{{"));
             self.curr_indent += self.indent;
@@ -781,13 +849,15 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
             self.curr_indent -= self.indent;
             try!(write!(self.writer, "\n"));
             try!(spaces(self.writer, self.curr_indent));
-            write!(self.writer, "}}")
+            try!(write!(self.writer, "}}"));
         }
+        Ok(())
     }
 
     fn emit_struct_field<F>(&mut self, name: &str, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
@@ -802,42 +872,52 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
     fn emit_tuple<F>(&mut self, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq(len, f)
     }
     fn emit_tuple_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq_elt(idx, f)
     }
 
     fn emit_tuple_struct<F>(&mut self, _: &str, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq(len, f)
     }
     fn emit_tuple_struct_arg<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         self.emit_seq_elt(idx, f)
     }
 
     fn emit_option<F>(&mut self, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
-    fn emit_option_none(&mut self) -> EncodeResult { self.emit_nil() }
+    fn emit_option_none(&mut self) -> EncodeResult {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
+        self.emit_nil()
+    }
     fn emit_option_some<F>(&mut self, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         f(self)
     }
 
     fn emit_seq<F>(&mut self, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if len == 0 {
-            write!(self.writer, "[]")
+            try!(write!(self.writer, "[]"));
         } else {
             try!(write!(self.writer, "["));
             self.curr_indent += self.indent;
@@ -845,13 +925,15 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
             self.curr_indent -= self.indent;
             try!(write!(self.writer, "\n"));
             try!(spaces(self.writer, self.curr_indent));
-            write!(self.writer, "]")
+            try!(write!(self.writer, "]"));
         }
+        Ok(())
     }
 
     fn emit_seq_elt<F>(&mut self, idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
@@ -864,8 +946,9 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
     fn emit_map<F>(&mut self, len: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if len == 0 {
-            write!(self.writer, "{{}}")
+            try!(write!(self.writer, "{{}}"));
         } else {
             try!(write!(self.writer, "{{"));
             self.curr_indent += self.indent;
@@ -873,38 +956,31 @@ impl<'a> ::Encoder for PrettyEncoder<'a> {
             self.curr_indent -= self.indent;
             try!(write!(self.writer, "\n"));
             try!(spaces(self.writer, self.curr_indent));
-            write!(self.writer, "}}")
+            try!(write!(self.writer, "}}"));
         }
+        Ok(())
     }
 
     fn emit_map_elt_key<F>(&mut self, idx: uint, mut f: F) -> EncodeResult where
         F: FnMut(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         if idx == 0 {
             try!(write!(self.writer, "\n"));
         } else {
             try!(write!(self.writer, ",\n"));
         }
         try!(spaces(self.writer, self.curr_indent));
-        // ref #12967, make sure to wrap a key in double quotes,
+        self.is_emitting_map_key = true;
-        // in the event that its of a type that omits them (eg numbers)
-        let mut buf = Vec::new();
-        // FIXME(14302) remove the transmute and unsafe block.
-        unsafe {
-            let mut check_encoder = PrettyEncoder::new(&mut buf);
-            try!(f(transmute(&mut check_encoder)));
-        }
-        let out = str::from_utf8(&buf[]).unwrap();
-        let needs_wrapping = out.char_at(0) != '"' && out.char_at_reverse(out.len()) != '"';
-        if needs_wrapping { try!(write!(self.writer, "\"")); }
         try!(f(self));
-        if needs_wrapping { try!(write!(self.writer, "\"")); }
+        self.is_emitting_map_key = false;
         Ok(())
     }
 
     fn emit_map_elt_val<F>(&mut self, _idx: uint, f: F) -> EncodeResult where
         F: FnOnce(&mut PrettyEncoder<'a>) -> EncodeResult,
     {
+        if self.is_emitting_map_key { return Err(EncoderError::BadHashmapKey); }
         try!(write!(self.writer, ": "));
         f(self)
     }