Rollup of 9 pull requests

.mailmap

@@ -5,8 +5,8 @@
 # email addresses.
 #
 
-Aaron Todd <github@opprobrio.us>
 Aaron Power <theaaronepower@gmail.com> Erin Power <xampprocky@gmail.com>
+Aaron Todd <github@opprobrio.us>
 Abhishek Chanda <abhishek.becs@gmail.com> Abhishek Chanda <abhishek@cloudscaling.com>
 Adolfo Ochagavía <aochagavia92@gmail.com>
 Adrien Tétar <adri-from-59@hotmail.fr>
@@ -29,8 +29,8 @@ Ariel Ben-Yehuda <arielb1@mail.tau.ac.il> Ariel Ben-Yehuda <ariel.byd@gmail.com>
 Ariel Ben-Yehuda <arielb1@mail.tau.ac.il> arielb1 <arielb1@mail.tau.ac.il>
 Austin Seipp <mad.one@gmail.com> <as@hacks.yi.org>
 Aydin Kim <ladinjin@hanmail.net> aydin.kim <aydin.kim@samsung.com>
-Bastian Kauschke <bastian_kauschke@hotmail.de>
 Barosl Lee <vcs@barosl.com> Barosl LEE <github@barosl.com>
+Bastian Kauschke <bastian_kauschke@hotmail.de>
 Ben Alpert <ben@benalpert.com> <spicyjalapeno@gmail.com>
 Ben Sago <ogham@users.noreply.github.com> Ben S <ogham@bsago.me>
 Ben Sago <ogham@users.noreply.github.com> Ben S <ogham@users.noreply.github.com>
@@ -46,22 +46,23 @@ Brian Anderson <banderson@mozilla.com> <banderson@mozilla.org>
 Brian Dawn <brian.t.dawn@gmail.com>
 Brian Leibig <brian@brianleibig.com> Brian Leibig <brian.leibig@gmail.com>
 Carl-Anton Ingmarsson <mail@carlanton.se> <ca.ingmarsson@gmail.com>
+Carol (Nichols || Goulding) <carol.nichols@gmail.com> <193874+carols10cents@users.noreply.github.com>
+Carol (Nichols || Goulding) <carol.nichols@gmail.com> <carol.nichols@gmail.com>
 Carol (Nichols || Goulding) <carol.nichols@gmail.com> <cnichols@thinkthroughmath.com>
-Carol (Nichols || Goulding) <carol.nichols@gmail.com> Carol Nichols <carol.nichols@gmail.com>
 Carol Willing <carolcode@willingconsulting.com>
 Chris C Cerami <chrisccerami@users.noreply.github.com> Chris C Cerami <chrisccerami@gmail.com>
 Chris Pressey <cpressey@gmail.com>
 Chris Thorn <chris@thorn.co> Chris Thorn <thorn@thoughtbot.com>
 Chris Vittal <christopher.vittal@gmail.com> Christopher Vittal <christopher.vittal@gmail.com>
-Christian Poveda <christianpoveda@protonmail.com> <z1mvader@protonmail.com>
 Christian Poveda <christianpoveda@protonmail.com> <cn.poveda.ruiz@gmail.com>
+Christian Poveda <christianpoveda@protonmail.com> <z1mvader@protonmail.com>
 Clark Gaebel <cg.wowus.cg@gmail.com> <cgaebel@mozilla.com>
 Clinton Ryan <clint.ryan3@gmail.com>
 Corey Richardson <corey@octayn.net> Elaine "See More" Nemo <corey@octayn.net>
 Cyryl Płotnicki <cyplo@cyplo.net>
 Damien Schoof <damien.schoof@gmail.com>
-Daniel Ramos <dan@daramos.com>
 Daniel J Rollins <drollins@financialforce.com>
+Daniel Ramos <dan@daramos.com>
 David Klein <david.klein@baesystemsdetica.com>
 David Manescu <david.manescu@gmail.com> <dman2626@uni.sydney.edu.au>
 David Ross <daboross@daboross.net>
@@ -70,18 +71,18 @@ Diggory Hardy <diggory.hardy@gmail.com> Diggory Hardy <github@dhardy.name>
 Dylan Braithwaite <dylanbraithwaite1@gmail.com> <mail@dylanb.me>
 Dzmitry Malyshau <kvarkus@gmail.com>
 E. Dunham <edunham@mozilla.com> edunham <edunham@mozilla.com>
+Eduard-Mihai Burtescu <edy.burt@gmail.com>
 Eduardo Bautista <me@eduardobautista.com> <=>
 Eduardo Bautista <me@eduardobautista.com> <mail@eduardobautista.com>
-Eduard-Mihai Burtescu <edy.burt@gmail.com>
 Elliott Slaughter <elliottslaughter@gmail.com> <eslaughter@mozilla.com>
 Elly Fong-Jones <elly@leptoquark.net>
 Eric Holk <eric.holk@gmail.com> <eholk@cs.indiana.edu>
 Eric Holk <eric.holk@gmail.com> <eholk@mozilla.com>
 Eric Holmes <eric@ejholmes.net>
 Eric Reed <ecreed@cs.washington.edu> <ereed@mozilla.com>
 Erick Tryzelaar <erick.tryzelaar@gmail.com> <etryzelaar@iqt.org>
-Esteban Küber <esteban@kuber.com.ar> <estebank@users.noreply.github.com>
 Esteban Küber <esteban@kuber.com.ar> <esteban@commure.com>
+Esteban Küber <esteban@kuber.com.ar> <estebank@users.noreply.github.com>
 Esteban Küber <esteban@kuber.com.ar> <github@kuber.com.ar>
 Evgeny Sologubov
 Falco Hirschenberger <falco.hirschenberger@gmail.com> <hirschen@itwm.fhg.de>
@@ -102,9 +103,9 @@ Herman J. Radtke III <herman@hermanradtke.com> Herman J. Radtke III <hermanradtk
 Ilyong Cho <ilyoan@gmail.com>
 Ivan Ivaschenko <defuz.net@gmail.com>
 J. J. Weber <jjweber@gmail.com>
+Jakub Adam Wieczorek <jakub.adam.wieczorek@gmail.com> <jakub.bukaj@yahoo.com>
 Jakub Adam Wieczorek <jakub.adam.wieczorek@gmail.com> <jakub@jakub.cc>
 Jakub Adam Wieczorek <jakub.adam.wieczorek@gmail.com> <jakubw@jakubw.net>
-Jakub Adam Wieczorek <jakub.adam.wieczorek@gmail.com> <jakub.bukaj@yahoo.com>
 James Deng <cnjamesdeng@gmail.com> <cnJamesDeng@gmail.com>
 James Miller <bladeon@gmail.com> <james@aatch.net>
 James Perry <james.austin.perry@gmail.com>
@@ -119,6 +120,7 @@ Jethro Beekman <github@jbeekman.nl>
 Jihyun Yu <j.yu@navercorp.com> <yjh0502@gmail.com>
 Jihyun Yu <j.yu@navercorp.com> jihyun <jihyun@nablecomm.com>
 Jihyun Yu <j.yu@navercorp.com> Jihyun Yu <jihyun@nclab.kaist.ac.kr>
+João Oliveira <hello@jxs.pt> joaoxsouls <joaoxsouls@gmail.com>
 Johann Hofmann <git@johann-hofmann.com> Johann <git@johann-hofmann.com>
 John Clements <clements@racket-lang.org> <clements@brinckerhoff.org>
 John Hodge <acessdev@gmail.com> John Hodge <tpg@mutabah.net>
@@ -129,7 +131,8 @@ Jonathan S <gereeter@gmail.com> Jonathan S <gereeter+code@gmail.com>
 Jonathan Turner <probata@hotmail.com>
 Jorge Aparicio <japaric@linux.com> <japaricious@gmail.com>
 Joseph Martin <pythoner6@gmail.com>
-João Oliveira <hello@jxs.pt> joaoxsouls <joaoxsouls@gmail.com>
+Joseph T. Lyons <JosephTLyons@gmail.com> <josephtlyons@gmail.com>
+Joseph T. Lyons <JosephTLyons@gmail.com> <JosephTLyons@users.noreply.github.com>
 Junyoung Cho <june0.cho@samsung.com>
 Jyun-Yan You <jyyou.tw@gmail.com> <jyyou@cs.nctu.edu.tw>
 Kang Seonghoon <kang.seonghoon@mearie.org> <public+git@mearie.org>
@@ -145,8 +148,6 @@ Lindsey Kuper <lindsey@composition.al> <lkuper@mozilla.com>
 Luke Metz <luke.metz@students.olin.edu>
 Luqman Aden <me@luqman.ca> <laden@csclub.uwaterloo.ca>
 Luqman Aden <me@luqman.ca> <laden@mozilla.com>
-NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm@gmail.com>
-NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm+github@gmail.com>
 Marcell Pardavi <marcell.pardavi@gmail.com>
 Margaret Meyerhofer <mmeyerho@andrew.cmu.edu> <mmeyerho@andrew>
 Mark Rousskov <mark.simulacrum@gmail.com>
@@ -167,12 +168,14 @@ Michael Woerister <michaelwoerister@posteo> <michaelwoerister@gmail>
 Mickaël Raybaud-Roig <raybaudroigm@gmail.com> m-r-r <raybaudroigm@gmail.com>
 Ms2ger <ms2ger@gmail.com> <Ms2ger@gmail.com>
 Mukilan Thiagarajan <mukilanthiagarajan@gmail.com>
+NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm@gmail.com>
+NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm+github@gmail.com>
 Nathan West <Lucretiel@gmail.com> <lucretiel@gmail.com>
 Nathan Wilson <wilnathan@gmail.com>
 Nathaniel Herman <nherman@post.harvard.edu> Nathaniel Herman <nherman@college.harvard.edu>
 Neil Pankey <npankey@gmail.com> <neil@wire.im>
-Nicole Mazzuca <npmazzuca@gmail.com>
 Nick Platt <platt.nicholas@gmail.com>
+Nicole Mazzuca <npmazzuca@gmail.com>
 Nif Ward <nif.ward@gmail.com>
 Oliver Schneider <oliver.schneider@kit.edu> oli-obk <github6541940@oli-obk.de>
 Oliver Schneider <oliver.schneider@kit.edu> Oliver 'ker' Schneider <rust19446194516@oli-obk.de>
@@ -230,8 +233,8 @@ Tim JIANG <p90eri@gmail.com>
 Tim Joseph Dumol <tim@timdumol.com>
 Torsten Weber <TorstenWeber12@gmail.com> <torstenweber12@gmail.com>
 Ty Overby <ty@pre-alpha.com>
-Ulrik Sverdrup <bluss@users.noreply.github.com> bluss <bluss>
 Ulrik Sverdrup <bluss@users.noreply.github.com> bluss <bluss@users.noreply.github.com>
+Ulrik Sverdrup <bluss@users.noreply.github.com> bluss <bluss>
 Ulrik Sverdrup <bluss@users.noreply.github.com> Ulrik Sverdrup <root@localhost>
 Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
 Vadim Petrochenkov <vadim.petrochenkov@gmail.com> petrochenkov <vadim.petrochenkov@gmail.com>

src/libcore/mem.rs

@@ -966,6 +966,9 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
 ///
 /// The compiler then knows to not make any incorrect assumptions or optimizations on this code.
 ///
+/// You can think of `MaybeUninit<T>` as being a bit like `Option<T>` but without
+/// any of the run-time tracking and without any of the safety checks.
+///
 /// ## out-pointers
 ///
 /// You can use `MaybeUninit<T>` to implement "out-pointers": instead of returning data

src/librustc/infer/error_reporting/mod.rs

@@ -652,7 +652,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         for sp in prior_arms {
                             err.span_label(*sp, format!(
                                 "this is found to be of type `{}`",
-                                self.resolve_type_vars_if_possible(&last_ty),
+                                self.resolve_vars_if_possible(&last_ty),
                             ));
                         }
                     } else if let Some(sp) = prior_arms.last() {
@@ -1278,7 +1278,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         &self,
         exp_found: &ty::error::ExpectedFound<Ty<'tcx>>,
     ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
-        let exp_found = self.resolve_type_vars_if_possible(exp_found);
+        let exp_found = self.resolve_vars_if_possible(exp_found);
         if exp_found.references_error() {
             return None;
         }
@@ -1291,7 +1291,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         &self,
         exp_found: &ty::error::ExpectedFound<T>,
     ) -> Option<(DiagnosticStyledString, DiagnosticStyledString)> {
-        let exp_found = self.resolve_type_vars_if_possible(exp_found);
+        let exp_found = self.resolve_vars_if_possible(exp_found);
         if exp_found.references_error() {
             return None;
         }

src/librustc/infer/error_reporting/need_type_info.rs

@@ -24,7 +24,7 @@ impl<'a, 'gcx, 'tcx> FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
         });
         match ty_opt {
             Some(ty) => {
-                let ty = self.infcx.resolve_type_vars_if_possible(&ty);
+                let ty = self.infcx.resolve_vars_if_possible(&ty);
                 ty.walk().any(|inner_ty| {
                     inner_ty == self.target_ty || match (&inner_ty.sty, &self.target_ty.sty) {
                         (&Infer(TyVar(a_vid)), &Infer(TyVar(b_vid))) => {
@@ -94,7 +94,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         span: Span,
         ty: Ty<'tcx>
     ) -> DiagnosticBuilder<'gcx> {
-        let ty = self.resolve_type_vars_if_possible(&ty);
+        let ty = self.resolve_vars_if_possible(&ty);
         let name = self.extract_type_name(&ty, None);
 
         let mut err_span = span;
@@ -166,7 +166,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         span: Span,
         ty: Ty<'tcx>
     ) -> DiagnosticBuilder<'gcx> {
-        let ty = self.resolve_type_vars_if_possible(&ty);
+        let ty = self.resolve_vars_if_possible(&ty);
         let name = self.extract_type_name(&ty, None);
 
         let mut err = struct_span_err!(self.tcx.sess,

src/librustc/infer/error_reporting/nice_region_error/placeholder_error.rs

@@ -210,11 +210,11 @@ impl NiceRegionError<'me, 'gcx, 'tcx> {
             _ => (),
         }
 
-        let expected_trait_ref = self.infcx.resolve_type_vars_if_possible(&ty::TraitRef {
+        let expected_trait_ref = self.infcx.resolve_vars_if_possible(&ty::TraitRef {
             def_id: trait_def_id,
             substs: expected_substs,
         });
-        let actual_trait_ref = self.infcx.resolve_type_vars_if_possible(&ty::TraitRef {
+        let actual_trait_ref = self.infcx.resolve_vars_if_possible(&ty::TraitRef {
             def_id: trait_def_id,
             substs: actual_substs,
         });

src/librustc/infer/fudge.rs

@@ -74,7 +74,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let (mut fudger, value) = self.probe(|snapshot| {
             match f() {
                 Ok(value) => {
-                    let value = self.resolve_type_vars_if_possible(&value);
+                    let value = self.resolve_vars_if_possible(&value);
 
                     // At this point, `value` could in principle refer
                     // to inference variables that have been created during

src/librustc/infer/mod.rs

@@ -1174,7 +1174,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     /// Process the region constraints and report any errors that
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
-    /// `resolve_type_vars_if_possible` as well as `fully_resolve`.
+    /// `resolve_vars_if_possible` as well as `fully_resolve`.
     pub fn resolve_regions_and_report_errors(
         &self,
         region_context: DefId,
@@ -1262,7 +1262,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn ty_to_string(&self, t: Ty<'tcx>) -> String {
-        self.resolve_type_vars_if_possible(&t).to_string()
+        self.resolve_vars_if_possible(&t).to_string()
     }
 
     pub fn tys_to_string(&self, ts: &[Ty<'tcx>]) -> String {
@@ -1271,7 +1271,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn trait_ref_to_string(&self, t: &ty::TraitRef<'tcx>) -> String {
-        self.resolve_type_vars_if_possible(t).to_string()
+        self.resolve_vars_if_possible(t).to_string()
     }
 
     /// If `TyVar(vid)` resolves to a type, return that type. Else, return the
@@ -1297,28 +1297,28 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.type_variables.borrow_mut().root_var(var)
     }
 
-    /// Where possible, replaces type/int/float variables in
+    /// Where possible, replaces type/const variables in
     /// `value` with their final value. Note that region variables
-    /// are unaffected. If a type variable has not been unified, it
+    /// are unaffected. If a type/const variable has not been unified, it
     /// is left as is. This is an idempotent operation that does
     /// not affect inference state in any way and so you can do it
     /// at will.
-    pub fn resolve_type_vars_if_possible<T>(&self, value: &T) -> T
+    pub fn resolve_vars_if_possible<T>(&self, value: &T) -> T
     where
         T: TypeFoldable<'tcx>,
     {
         if !value.needs_infer() {
             return value.clone(); // avoid duplicated subst-folding
         }
-        let mut r = resolve::OpportunisticTypeResolver::new(self);
+        let mut r = resolve::OpportunisticVarResolver::new(self);
         value.fold_with(&mut r)
     }
 
     /// Returns first unresolved variable contained in `T`. In the
     /// process of visiting `T`, this will resolve (where possible)
     /// type variables in `T`, but it never constructs the final,
     /// resolved type, so it's more efficient than
-    /// `resolve_type_vars_if_possible()`.
+    /// `resolve_vars_if_possible()`.
     pub fn unresolved_type_vars<T>(&self, value: &T) -> Option<(Ty<'tcx>, Option<Span>)>
     where
         T: TypeFoldable<'tcx>,
@@ -1389,7 +1389,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     where
         M: FnOnce(String) -> DiagnosticBuilder<'tcx>,
     {
-        let actual_ty = self.resolve_type_vars_if_possible(&actual_ty);
+        let actual_ty = self.resolve_vars_if_possible(&actual_ty);
         debug!("type_error_struct_with_diag({:?}, {:?})", sp, actual_ty);
 
         // Don't report an error if actual type is `Error`.
@@ -1446,7 +1446,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         ty: Ty<'tcx>,
         span: Span,
     ) -> bool {
-        let ty = self.resolve_type_vars_if_possible(&ty);
+        let ty = self.resolve_vars_if_possible(&ty);
 
         // Even if the type may have no inference variables, during
         // type-checking closure types are in local tables only.

src/librustc/infer/opaque_types/mod.rs

@@ -286,7 +286,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         let tcx = self.tcx;
 
-        let concrete_ty = self.resolve_type_vars_if_possible(&opaque_defn.concrete_ty);
+        let concrete_ty = self.resolve_vars_if_possible(&opaque_defn.concrete_ty);
 
         debug!("constrain_opaque_type: concrete_ty={:?}", concrete_ty);
 

src/librustc/infer/outlives/env.rs

@@ -168,7 +168,7 @@ impl<'a, 'gcx: 'tcx, 'tcx: 'a> OutlivesEnvironment<'tcx> {
         debug!("add_implied_bounds()");
 
         for &ty in fn_sig_tys {
-            let ty = infcx.resolve_type_vars_if_possible(&ty);
+            let ty = infcx.resolve_vars_if_possible(&ty);
             debug!("add_implied_bounds: ty = {}", ty);
             let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty, span);
             self.add_outlives_bounds(Some(infcx), implied_bounds)

src/librustc/infer/outlives/obligations.rs

@@ -177,7 +177,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                 sup_type, sub_region, origin
             );
 
-            let sup_type = self.resolve_type_vars_if_possible(&sup_type);
+            let sup_type = self.resolve_vars_if_possible(&sup_type);
 
             if let Some(region_bound_pairs) = region_bound_pairs_map.get(&body_id) {
                 let outlives = &mut TypeOutlives::new(
@@ -215,7 +215,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
             implicit_region_bound,
             param_env,
         );
-        let ty = self.resolve_type_vars_if_possible(&ty);
+        let ty = self.resolve_vars_if_possible(&ty);
         outlives.type_must_outlive(origin, ty, region);
     }
 }

src/librustc/infer/resolve.rs

@@ -1,28 +1,28 @@
 use super::{InferCtxt, FixupError, FixupResult, Span, type_variable::TypeVariableOrigin};
 use crate::mir::interpret::ConstValue;
-use crate::ty::{self, Ty, TyCtxt, TypeFoldable, InferConst};
+use crate::ty::{self, Ty, Const, TyCtxt, TypeFoldable, InferConst, TypeFlags};
 use crate::ty::fold::{TypeFolder, TypeVisitor};
 
 ///////////////////////////////////////////////////////////////////////////
-// OPPORTUNISTIC TYPE RESOLVER
+// OPPORTUNISTIC VAR RESOLVER
 
-/// The opportunistic type resolver can be used at any time. It simply replaces
-/// type variables that have been unified with the things they have
+/// The opportunistic resolver can be used at any time. It simply replaces
+/// type/const variables that have been unified with the things they have
 /// been unified with (similar to `shallow_resolve`, but deep). This is
 /// useful for printing messages etc but also required at various
 /// points for correctness.
-pub struct OpportunisticTypeResolver<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
+pub struct OpportunisticVarResolver<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
 }
 
-impl<'a, 'gcx, 'tcx> OpportunisticTypeResolver<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> OpportunisticVarResolver<'a, 'gcx, 'tcx> {
     #[inline]
     pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>) -> Self {
-        OpportunisticTypeResolver { infcx }
+        OpportunisticVarResolver { infcx }
     }
 }
 
-impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for OpportunisticTypeResolver<'a, 'gcx, 'tcx> {
+impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for OpportunisticVarResolver<'a, 'gcx, 'tcx> {
     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
         self.infcx.tcx
     }
@@ -31,8 +31,17 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for OpportunisticTypeResolver<'a, 'g
         if !t.has_infer_types() {
             t // micro-optimize -- if there is nothing in this type that this fold affects...
         } else {
-            let t0 = self.infcx.shallow_resolve(t);
-            t0.super_fold_with(self)
+            let t = self.infcx.shallow_resolve(t);
+            t.super_fold_with(self)
+        }
+    }
+
+    fn fold_const(&mut self, ct: &'tcx Const<'tcx>) -> &'tcx Const<'tcx> {
+        if !ct.has_type_flags(TypeFlags::HAS_CT_INFER) {
+            ct // micro-optimize -- if there is nothing in this const that this fold affects...
+        } else {
+            let ct = self.infcx.shallow_resolve(ct);
+            ct.super_fold_with(self)
         }
     }
 }