Add len() method to OutputTypes

src/librustc/session/config.rs

@@ -246,6 +246,10 @@ impl OutputTypes {
         self.0.values()
     }
 
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
     // True if any of the output types require codegen or linking.
     pub fn should_trans(&self) -> bool {
         self.0.keys().any(|k| match *k {

src/librustc_driver/driver.rs

@@ -168,7 +168,7 @@ pub fn compile_input(trans: Box<TransCrate>,
 
         write_out_deps(sess, &outputs, &output_paths);
         if sess.opts.output_types.contains_key(&OutputType::DepInfo) &&
-            sess.opts.output_types.keys().count() == 1 {
+            sess.opts.output_types.len() == 1 {
             return Ok(())
         }
 

src/librustc_metadata/encoder.rs

@@ -835,7 +835,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
 
     fn metadata_output_only(&self) -> bool {
         // MIR optimisation can be skipped when we're just interested in the metadata.
-        self.tcx.sess.opts.output_types.keys().count() == 1 &&
+        self.tcx.sess.opts.output_types.len() == 1 &&
             self.tcx.sess.opts.output_types.contains_key(&OutputType::Metadata)
     }