Review comments.

src/librustc/middle/lang_items.rs

@@ -31,7 +31,7 @@ impl<'tcx> TyCtxt<'tcx> {
         })
     }
 
-    pub fn fn_trait_lang_item(&self, id: DefId) -> Option<ty::ClosureKind> {
+    pub fn fn_trait_kind_from_lang_item(&self, id: DefId) -> Option<ty::ClosureKind> {
         let items = self.lang_items();
         match Some(id) {
             x if x == items.fn_trait() => Some(ty::ClosureKind::Fn),

src/librustc/traits/select.rs

@@ -1634,7 +1634,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) -> Result<(), SelectionError<'tcx>> {
-        let kind = match self.tcx().fn_trait_lang_item(obligation.predicate.def_id()) {
+        let kind = match self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) {
             Some(k) => k,
             None => {
                 return Ok(());
@@ -1677,7 +1677,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) -> Result<(), SelectionError<'tcx>> {
         // We provide impl of all fn traits for fn pointers.
-        if self.tcx().fn_trait_lang_item(obligation.predicate.def_id()).is_none() {
+        if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() {
             return Ok(());
         }
 
@@ -2889,7 +2889,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let kind = self
             .tcx()
-            .fn_trait_lang_item(obligation.predicate.def_id())
+            .fn_trait_kind_from_lang_item(obligation.predicate.def_id())
             .unwrap_or_else(|| bug!("closure candidate for non-fn trait {:?}", obligation));
 
         // Okay to skip binder because the substs on closure types never

src/librustc/ty/instance.rs

@@ -450,7 +450,7 @@ fn resolve_associated_item<'tcx>(
             substs: generator_data.substs,
         }),
         traits::VtableClosure(closure_data) => {
-            let trait_closure_kind = tcx.fn_trait_lang_item(trait_id).unwrap();
+            let trait_closure_kind = tcx.fn_trait_kind_from_lang_item(trait_id).unwrap();
             Some(Instance::resolve_closure(
                 tcx,
                 closure_data.closure_def_id,

src/librustc/ty/print/pretty.rs

@@ -724,7 +724,7 @@ pub trait PrettyPrinter<'tcx>:
             let mut resugared = false;
 
             // Special-case `Fn(...) -> ...` and resugar it.
-            let fn_trait_kind = self.tcx().fn_trait_lang_item(principal.def_id);
+            let fn_trait_kind = self.tcx().fn_trait_kind_from_lang_item(principal.def_id);
             if !self.tcx().sess.verbose() && fn_trait_kind.is_some() {
                 if let ty::Tuple(ref args) = principal.substs.type_at(0).kind {
                     let mut projections = predicates.projection_bounds();

src/librustc_mir/shim.rs

@@ -40,7 +40,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> &'tcx
         ),
         ty::InstanceDef::FnPtrShim(def_id, ty) => {
             let trait_ = tcx.trait_of_item(def_id).unwrap();
-            let adjustment = match tcx.fn_trait_lang_item(trait_) {
+            let adjustment = match tcx.fn_trait_kind_from_lang_item(trait_) {
                 Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
                 Some(ty::ClosureKind::FnMut) | Some(ty::ClosureKind::Fn) => Adjustment::Deref,
                 None => bug!("fn pointer {:?} is not an fn", ty),

src/librustc_typeck/check/closure.rs

@@ -174,8 +174,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.deduce_sig_from_projection(None, &pb)
                     })
                     .next();
-                let kind =
-                    object_type.principal_def_id().and_then(|did| self.tcx.fn_trait_lang_item(did));
+                let kind = object_type
+                    .principal_def_id()
+                    .and_then(|did| self.tcx.fn_trait_kind_from_lang_item(did));
                 (sig, kind)
             }
             ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
@@ -213,7 +214,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // many viable options, so pick the most restrictive.
         let expected_kind = self
             .obligations_for_self_ty(expected_vid)
-            .filter_map(|(tr, _)| self.tcx.fn_trait_lang_item(tr.def_id()))
+            .filter_map(|(tr, _)| self.tcx.fn_trait_kind_from_lang_item(tr.def_id()))
             .fold(None, |best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
 
         (expected_sig, expected_kind)
@@ -236,7 +237,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let trait_ref = projection.to_poly_trait_ref(tcx);
 
-        let is_fn = tcx.fn_trait_lang_item(trait_ref.def_id()).is_some();
+        let is_fn = tcx.fn_trait_kind_from_lang_item(trait_ref.def_id()).is_some();
         let gen_trait = tcx.require_lang_item(lang_items::GeneratorTraitLangItem, cause_span);
         let is_gen = gen_trait == trait_ref.def_id();
         if !is_fn && !is_gen {

src/librustdoc/clean/utils.rs

@@ -138,7 +138,7 @@ pub fn external_generic_args(
 
     match trait_did {
         // Attempt to sugar an external path like Fn<(A, B,), C> to Fn(A, B) -> C
-        Some(did) if cx.tcx.fn_trait_lang_item(did).is_some() => {
+        Some(did) if cx.tcx.fn_trait_kind_from_lang_item(did).is_some() => {
             assert!(ty_kind.is_some());
             let inputs = match ty_kind {
                 Some(ty::Tuple(ref tys)) => tys.iter().map(|t| t.expect_ty().clean(cx)).collect(),