Specify usability of inspect_typeck in comment.

compiler/rustc_hir_typeck/src/lib.rs

@@ -155,6 +155,8 @@ fn diagnostic_only_typeck<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &ty::T
 
 /// Same as `typeck` but `inspect` is invoked on evaluation of each root obligation.
 /// Inspecting obligations only works with the new trait solver.
+/// This function is *only to be used* by external tools, it should not be
+/// called from within rustc. Note, this is not a query, and thus is not cached.
 pub fn inspect_typeck<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -72,8 +72,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
     }
 
     fn collect_remaining_errors(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
-        let errors = self
-            .obligations
+        self.obligations
             .drain(..)
             .map(|obligation| {
                 let code = infcx.probe(|_| {
@@ -102,9 +101,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                     root_obligation: obligation,
                 }
             })
-            .collect();
-
-        errors
+            .collect()
     }
 
     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {