Fix some some duplicate words.

src/librustc/session/config.rs

@@ -1355,7 +1355,7 @@ pub mod nightly_options {
                     early_error(ErrorOutputType::default(), &msg);
                 }
                 OptionStability::UnstableButNotReally => {
-                    let msg = format!("the option `{}` is is unstable and should \
+                    let msg = format!("the option `{}` is unstable and should \
                                        only be used on the nightly compiler, but \
                                        it is currently accepted for backwards \
                                        compatibility; this will soon change, \

src/librustc/traits/project.rs

@@ -40,7 +40,7 @@ use std::rc::Rc;
 pub enum ProjectionMode {
     /// FIXME (#32205)
     /// At coherence-checking time, we're still constructing the
-    /// specialization graph, and thus we only project project
+    /// specialization graph, and thus we only project
     /// non-`default` associated types that are defined directly in
     /// the applicable impl. (This behavior should be improved over
     /// time, to allow for successful projections modulo cycles

src/librustc/ty/trait_def.rs

@@ -176,7 +176,7 @@ impl<'tcx> TraitDef<'tcx> {
     /// Records a trait-to-implementation mapping for a non-local impl.
     ///
     /// The `parent_impl` is the immediately-less-specialized impl, or the
-    /// trait's def ID if the impl is is not a specialization -- information that
+    /// trait's def ID if the impl is not a specialization -- information that
     /// should be pulled from the metadata.
     pub fn record_remote_impl(&self,
                               tcx: &TyCtxt<'tcx>,

src/librustc/ty/wf.rs

@@ -268,7 +268,7 @@ impl<'a,'tcx> WfPredicates<'a,'tcx> {
     /// into `self.out`.
     fn compute_projection(&mut self, data: ty::ProjectionTy<'tcx>) {
         // A projection is well-formed if (a) the trait ref itself is
-        // WF WF and (b) the trait-ref holds.  (It may also be
+        // WF and (b) the trait-ref holds.  (It may also be
         // normalizable and be WF that way.)
 
         self.compute_trait_ref(&data.trait_ref);