Cfg off functions only needed for rustc-serialize or serde

src/decoder/mod.rs

@@ -1,6 +1,9 @@
 use std::error;
 use std::fmt;
+
+#[cfg(feature = "rustc-serialize")]
 use std::collections::{btree_map, BTreeMap};
+#[cfg(feature = "rustc-serialize")]
 use std::iter::Peekable;
 
 use Value;
@@ -19,7 +22,9 @@ pub struct Decoder {
     /// whether fields were decoded or not.
     pub toml: Option<Value>,
     cur_field: Option<String>,
+    #[cfg(feature = "rustc-serialize")]
     cur_map: Peekable<btree_map::IntoIter<String, Value>>,
+    #[cfg(feature = "rustc-serialize")]
     leftover_map: ::Table,
 }
 
@@ -115,30 +120,39 @@ impl Decoder {
     /// This decoder can be passed to the `Decodable` methods or driven
     /// manually.
     pub fn new(toml: Value) -> Decoder {
-        Decoder {
+        Decoder::new_empty(Some(toml), None)
-            toml: Some(toml),
-            cur_field: None,
-            leftover_map: BTreeMap::new(),
-            cur_map: BTreeMap::new().into_iter().peekable(),
-        }
     }
 
     fn sub_decoder(&self, toml: Option<Value>, field: &str) -> Decoder {
-        Decoder {
+        let cur_field = if field.is_empty() {
-            toml: toml,
-            cur_field: if field.is_empty() {
             self.cur_field.clone()
         } else {
             match self.cur_field {
                 None => Some(field.to_string()),
                 Some(ref s) => Some(format!("{}.{}", s, field))
             }
-            },
+        };
+        Decoder::new_empty(toml, cur_field)
+    }
+
+    #[cfg(feature = "rustc-serialize")]
+    fn new_empty(toml: Option<Value>, cur_field: Option<String>) -> Decoder {
+        Decoder {
+            toml: toml,
+            cur_field: cur_field,
             leftover_map: BTreeMap::new(),
             cur_map: BTreeMap::new().into_iter().peekable(),
         }
     }
 
+    #[cfg(not(feature = "rustc-serialize"))]
+    fn new_empty(toml: Option<Value>, cur_field: Option<String>) -> Decoder {
+        Decoder {
+            toml: toml,
+            cur_field: cur_field,
+        }
+    }
+
     fn err(&self, kind: DecodeErrorKind) -> DecodeError {
         DecodeError {
             field: self.cur_field.clone(),

src/encoder/mod.rs

@@ -113,6 +113,7 @@ impl Encoder {
         }
     }
 
+    #[cfg(feature = "rustc-serialize")]
     fn seq<F>(&mut self, f: F) -> Result<(), Error>
         where F: FnOnce(&mut Encoder) -> Result<(), Error>
     {
@@ -132,6 +133,7 @@ impl Encoder {
         }
     }
 
+    #[cfg(feature = "rustc-serialize")]
     fn table<F>(&mut self, f: F) -> Result<(), Error>
         where F: FnOnce(&mut Encoder) -> Result<(), Error>
     {
@@ -154,6 +156,7 @@ impl Encoder {
         }
     }
 
+    #[cfg(feature = "serde")]
     fn table_begin(&mut self) -> Result<Self, Error> {
         match self.state {
             State::NextMapKey => Err(Error::InvalidMapKeyLocation),
@@ -161,6 +164,7 @@ impl Encoder {
         }
     }
 
+    #[cfg(feature = "serde")]
     fn table_end(&mut self, mut state: Self) -> Result<(), Error> {
         match state.state {
             State::NextKey(key) => {