libstd: Remove some residual mutable fields

src/libstd/ebml.rs

@@ -600,11 +600,18 @@ pub mod writer {
     use core::vec;
 
     // ebml writing
+    #[cfg(stage0)]
     pub struct Encoder {
         writer: @io::Writer,
         priv mut size_positions: ~[uint],
     }
 
+    #[cfg(not(stage0))]
+    pub struct Encoder {
+        writer: @io::Writer,
+        priv size_positions: ~[uint],
+    }
+
     fn write_sized_vuint(w: @io::Writer, n: uint, size: uint) {
         match size {
             1u => w.write(&[0x80u8 | (n as u8)]),
@@ -625,9 +632,22 @@ pub mod writer {
         fail!(fmt!("vint to write too big: %?", n));
     }
 
+    #[cfg(stage0)]
     pub fn Encoder(w: @io::Writer) -> Encoder {
         let size_positions: ~[uint] = ~[];
-        Encoder { writer: w, mut size_positions: size_positions }
+        Encoder {
+            writer: w,
+            mut size_positions: size_positions
+        }
+    }
+
+    #[cfg(not(stage0))]
+    pub fn Encoder(w: @io::Writer) -> Encoder {
+        let size_positions: ~[uint] = ~[];
+        Encoder {
+            writer: w,
+            size_positions: size_positions
+        }
     }
 
     // FIXME (#2741): Provide a function to write the standard ebml header.

src/libstd/json.rs

@@ -220,11 +220,18 @@ impl serialize::Encoder for Encoder {
     }
 }
 
+#[cfg(stage0)]
 pub struct PrettyEncoder {
     priv wr: @io::Writer,
     priv mut indent: uint,
 }
 
+#[cfg(not(stage0))]
+pub struct PrettyEncoder {
+    priv wr: @io::Writer,
+    priv indent: uint,
+}
+
 pub fn PrettyEncoder(wr: @io::Writer) -> PrettyEncoder {
     PrettyEncoder {
         wr: wr,
@@ -838,10 +845,16 @@ pub fn from_str(s: &str) -> Result<Json, Error> {
     }
 }
 
+#[cfg(stage0)]
 pub struct Decoder {
     priv mut stack: ~[Json],
 }
 
+#[cfg(not(stage0))]
+pub struct Decoder {
+    priv stack: ~[Json],
+}
+
 pub fn Decoder(json: Json) -> Decoder {
     Decoder {
         stack: ~[json]