Fix raw value compilation on rustc older than 1.20

Author: dtolnay

src/read.rs

@@ -166,11 +166,20 @@ where
 {
     /// Create a JSON input source to read from a std::io input stream.
     pub fn new(reader: R) -> Self {
-        IoRead {
-            iter: LineColIterator::new(reader.bytes()),
-            ch: None,
-            #[cfg(feature = "raw_value")]
-            raw_buffer: None,
+        #[cfg(not(feature = "raw_value"))]
+        {
+            IoRead {
+                iter: LineColIterator::new(reader.bytes()),
+                ch: None,
+            }
+        }
+        #[cfg(feature = "raw_value")]
+        {
+            IoRead {
+                iter: LineColIterator::new(reader.bytes()),
+                ch: None,
+                raw_buffer: None,
+            }
         }
     }
 }
@@ -351,11 +360,20 @@ where
 impl<'a> SliceRead<'a> {
     /// Create a JSON input source to read from a slice of bytes.
     pub fn new(slice: &'a [u8]) -> Self {
-        SliceRead {
-            slice: slice,
-            index: 0,
-            #[cfg(feature = "raw_value")]
-            raw_buffering_start_index: 0,
+        #[cfg(not(feature = "raw_value"))]
+        {
+            SliceRead {
+                slice: slice,
+                index: 0,
+            }
+        }
+        #[cfg(feature = "raw_value")]
+        {
+            SliceRead {
+                slice: slice,
+                index: 0,
+                raw_buffering_start_index: 0,
+            }
         }
     }
 
@@ -531,10 +549,18 @@ impl<'a> Read<'a> for SliceRead<'a> {
 impl<'a> StrRead<'a> {
     /// Create a JSON input source to read from a UTF-8 string.
     pub fn new(s: &'a str) -> Self {
-        StrRead {
-            delegate: SliceRead::new(s.as_bytes()),
-            #[cfg(feature = "raw_value")]
-            data: s,
+        #[cfg(not(feature = "raw_value"))]
+        {
+            StrRead {
+                delegate: SliceRead::new(s.as_bytes()),
+            }
+        }
+        #[cfg(feature = "raw_value")]
+        {
+            StrRead {
+                delegate: SliceRead::new(s.as_bytes()),
+                data: s,
+            }
         }
     }
 }