auto merge of #12361 : sfackler/rust/rustdoc-test-extern, r=alexcrichton

Author: bors

src/libextra/json.rs

@@ -59,6 +59,7 @@ the code for these traits: `#[deriving(Decodable, Encodable)]`
 To encode using Encodable :
 
 ```rust
+extern crate extra;
 extern crate serialize;
 use extra::json;
 use std::io;
@@ -98,6 +99,7 @@ A basic `ToJson` example using a TreeMap of attribute name / attribute value:
 
 
 ```rust
+extern crate extra;
 extern crate collections;
 
 use extra::json;
@@ -128,6 +130,7 @@ fn main() {
 To decode a JSON string using `Decodable` trait :
 
 ```rust
+extern crate extra;
 extern crate serialize;
 use serialize::Decodable;
 
@@ -154,6 +157,7 @@ Create a struct called TestStruct1 and serialize and deserialize it to and from
 using the serialization API, using the derived serialization code.
 
 ```rust
+extern crate extra;
 extern crate serialize;
 use extra::json;
 use serialize::{Encodable, Decodable};
@@ -186,6 +190,7 @@ This example use the ToJson impl to deserialize the JSON string.
 Example of `ToJson` trait implementation for TestStruct1.
 
 ```rust
+extern crate extra;
 extern crate serialize;
 extern crate collections;
 

src/librustdoc/test.rs

@@ -144,11 +144,13 @@ fn maketest(s: &str, cratename: &str) -> ~str {
 #[deny(warnings)];
 #[allow(unused_variable, dead_assignment, unused_mut, attribute_usage, dead_code)];
 ";
-    if s.contains("extra") {
-        prog.push_str("extern crate extra;\n");
-    }
-    if s.contains(cratename) {
-        prog.push_str(format!("extern crate {};\n", cratename));
+    if !s.contains("extern crate") {
+        if s.contains("extra") {
+            prog.push_str("extern crate extra;\n");
+        }
+        if s.contains(cratename) {
+            prog.push_str(format!("extern crate {};\n", cratename));
+        }
     }
     if s.contains("fn main") {
         prog.push_str(s);