update comments

compiler/rustc_infer/src/infer/canonical/mod.rs

@@ -49,7 +49,6 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// At the end of processing, the substitution S (once
     /// canonicalized) then represents the values that you computed
     /// for each of the canonical inputs to your query.
-
     pub fn instantiate_canonical_with_fresh_inference_vars<T>(
         &self,
         span: Span,

compiler/rustc_infer/src/infer/mod.rs

@@ -558,9 +558,9 @@ impl<'tcx> fmt::Display for FixupError<'tcx> {
     }
 }
 
-/// Helper type of a temporary returned by `tcx.infer_ctxt()`.
-/// Necessary because we can't write the following bound:
-/// `F: for<'b, 'tcx> where 'tcx FnOnce(InferCtxt<'b, 'tcx>)`.
+/// A temporary returned by `tcx.infer_ctxt()`. This is necessary
+/// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
+/// without using `Rc` or something similar.
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
     fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,

compiler/rustc_typeck/src/check/inherited.rs

@@ -68,9 +68,9 @@ impl<'a, 'tcx> Deref for Inherited<'a, 'tcx> {
     }
 }
 
-/// Helper type of a temporary returned by `Inherited::build(...)`.
-/// Necessary because we can't write the following bound:
-/// `F: for<'b, 'tcx> where 'tcx FnOnce(Inherited<'b, 'tcx>)`.
+/// A temporary returned by `Inherited::build(...)`. This is necessary
+/// for multiple `InferCtxt` to share the same `in_progress_typeck_results`
+/// without using `Rc` or something similar.
 pub struct InheritedBuilder<'tcx> {
     infcx: infer::InferCtxtBuilder<'tcx>,
     def_id: LocalDefId,