Add a new normalization query just for mir constants

compiler/rustc_infer/src/infer/resolve.rs

 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use super::{FixupError, FixupResult, InferCtxt, Span};
+use rustc_middle::mir;
 use rustc_middle::ty::fold::{TypeFolder, TypeVisitor};
 use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable};
 
@@ -46,6 +47,10 @@ fn fold_const(&mut self, ct: &'tcx Const<'tcx>) -> &'tcx Const<'tcx> {
             ct.super_fold_with(self)
         }
     }
+
+    fn fold_mir_const(&mut self, constant: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        constant.super_fold_with(self)
+    }
 }
 
 /// The opportunistic region resolver opportunistically resolves regions

compiler/rustc_middle/src/mir/mod.rs

@@ -2410,7 +2410,8 @@ pub struct Constant<'tcx> {
     pub literal: ConstantKind<'tcx>,
 }
 
-#[derive(Clone, Copy, PartialEq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
+#[derive(Lift)]
 pub enum ConstantKind<'tcx> {
     /// This constant came from the type system
     Ty(&'tcx ty::Const<'tcx>),
@@ -2709,7 +2710,13 @@ fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
             ty::FnDef(..) => {}
             _ => write!(fmt, "const ")?,
         }
-        match self.literal {
+        Display::fmt(&self.literal, fmt)
+    }
+}
+
+impl<'tcx> Display for ConstantKind<'tcx> {
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
+        match *self {
             ConstantKind::Ty(c) => pretty_print_const(c, fmt, true),
             ConstantKind::Val(val, ty) => pretty_print_const_value(val, ty, fmt, true),
         }

compiler/rustc_middle/src/mir/type_foldable.rs

@@ -348,6 +348,10 @@ fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow
 }
 
 impl<'tcx> TypeFoldable<'tcx> for ConstantKind<'tcx> {
+    fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
+        folder.fold_mir_const(self)
+    }
+
     fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
         match self {
             ConstantKind::Ty(c) => ConstantKind::Ty(c.fold_with(folder)),

compiler/rustc_middle/src/query/mod.rs

@@ -1482,6 +1482,13 @@
         desc { "normalizing `{}`", goal.value }
     }
 
+    /// Do not call this query directly: invoke `normalize_erasing_regions` instead.
+    query normalize_mir_const_after_erasing_regions(
+        goal: ParamEnvAnd<'tcx, mir::ConstantKind<'tcx>>
+    ) -> mir::ConstantKind<'tcx> {
+        desc { "normalizing `{}`", goal.value }
+    }
+
     query implied_outlives_bounds(
         goal: CanonicalTyGoal<'tcx>
     ) -> Result<

compiler/rustc_middle/src/ty/erase_regions.rs

+use crate::mir;
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::{self, Ty, TyCtxt, TypeFlags};
 
@@ -65,4 +66,8 @@ fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
             _ => self.tcx.lifetimes.re_erased,
         }
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        c.super_fold_with(self)
+    }
 }

compiler/rustc_middle/src/ty/fold.rs

@@ -30,6 +30,7 @@
 //!
 //! These methods return true to indicate that the visitor has found what it is
 //! looking for, and does not need to visit anything else.
+use crate::mir;
 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -179,6 +180,10 @@ fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
     fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
         c.super_fold_with(self)
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        bug!("most type folders should not be folding MIR datastructures: {:?}", c)
+    }
 }
 
 pub trait TypeVisitor<'tcx>: Sized {

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -7,6 +7,7 @@
 //! `normalize_generic_arg_after_erasing_regions` query for each type
 //! or constant found within. (This underlying query is what is cached.)
 
+use crate::mir;
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{self, Ty, TyCtxt};
@@ -101,4 +102,9 @@ fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
         let arg = self.param_env.and(c.into());
         self.tcx.normalize_generic_arg_after_erasing_regions(arg).expect_const()
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        let arg = self.param_env.and(c);
+        self.tcx.normalize_mir_const_after_erasing_regions(arg)
+    }
 }

compiler/rustc_middle/src/ty/subst.rs

 // Type substitutions.
 
+use crate::mir;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts};
@@ -503,6 +504,10 @@ fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
             c.super_fold_with(self)
         }
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        c.super_fold_with(self)
+    }
 }
 
 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {

compiler/rustc_mir/src/monomorphize/collector.rs

@@ -184,7 +184,6 @@
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::GrowableBitSet;
-use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::interpret::{AllocId, ConstValue};
 use rustc_middle::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar};
 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
@@ -193,6 +192,7 @@
 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast};
 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
 use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::{middle::codegen_fn_attrs::CodegenFnAttrFlags, mir::visit::TyContext};
 use rustc_session::config::EntryFnType;
 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
 use smallvec::SmallVec;
@@ -638,6 +638,35 @@ fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
         self.super_rvalue(rvalue, location);
     }
 
+    /// This does not walk the constant, as it has been handled entirely here and trying
+    /// to walk it would attempt to evaluate the `ty::Const` inside, which doesn't necessarily
+    /// work, as some constants cannot be represented in the type system.
+    fn visit_constant(&mut self, constant: &mir::Constant<'tcx>, location: Location) {
+        let literal = self.monomorphize(constant.literal);
+        let val = match literal {
+            mir::ConstantKind::Val(val, _) => val,
+            mir::ConstantKind::Ty(ct) => match ct.val {
+                ty::ConstKind::Value(val) => val,
+                ty::ConstKind::Unevaluated(ct) => {
+                    let param_env = ty::ParamEnv::reveal_all();
+                    match self.tcx.const_eval_resolve(param_env, ct, None) {
+                        // The `monomorphize` call should have evaluated that constant already.
+                        Ok(val) => val,
+                        Err(ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted) => return,
+                        Err(ErrorHandled::TooGeneric) => span_bug!(
+                            self.body.source_info(location).span,
+                            "collection encountered polymorphic constant: {:?}",
+                            literal
+                        ),
+                    }
+                }
+                _ => return,
+            },
+        };
+        collect_const_value(self.tcx, val, self.output);
+        self.visit_ty(literal.ty(), TyContext::Location(location));
+    }
+
     fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
         debug!("visiting const {:?} @ {:?}", *constant, location);
 

compiler/rustc_mir/src/util/pretty.rs

@@ -452,7 +452,11 @@ fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
                 match literal {
                     ConstantKind::Ty(literal) => self.push(&format!("+ literal: {:?}", literal)),
                     ConstantKind::Val(val, ty) => {
-                        self.push(&format!("+ literal: {:?}, {}", val, ty))
+                        // To keep the diffs small, we render this almost like we render ty::Const
+                        self.push(&format!(
+                            "+ literal: Const {{ ty: {}, val: Value({:?}) }}",
+                            ty, val
+                        ))
                     }
                 }
             }

compiler/rustc_query_impl/src/keys.rs

@@ -255,6 +255,15 @@ fn default_span(&self, _: TyCtxt<'_>) -> Span {
     }
 }
 
+impl<'tcx> Key for mir::ConstantKind<'tcx> {
+    fn query_crate(&self) -> CrateNum {
+        LOCAL_CRATE
+    }
+    fn default_span(&self, _: TyCtxt<'_>) -> Span {
+        DUMMY_SP
+    }
+}
+
 impl<'tcx> Key for &'tcx ty::Const<'tcx> {
     fn query_crate(&self) -> CrateNum {
         LOCAL_CRATE

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -10,6 +10,7 @@
 use rustc_data_structures::sso::SsoHashMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_infer::traits::Normalized;
+use rustc_middle::mir;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -214,4 +215,8 @@ fn fold_const(&mut self, constant: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tc
         let constant = constant.super_fold_with(self);
         constant.eval(self.infcx.tcx, self.param_env)
     }
+
+    fn fold_mir_const(&mut self, constant: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        constant.super_fold_with(self)
+    }
 }

compiler/rustc_traits/src/normalize_erasing_regions.rs

 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::GenericArg;
 use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt, TypeFoldable};
 use rustc_trait_selection::traits::query::normalize::AtExt;
 use rustc_trait_selection::traits::{Normalized, ObligationCause};
 use std::sync::atomic::Ordering;
 
 crate fn provide(p: &mut Providers) {
-    *p = Providers { normalize_generic_arg_after_erasing_regions, ..*p };
+    *p = Providers {
+        normalize_generic_arg_after_erasing_regions: |tcx, goal| {
+            debug!("normalize_generic_arg_after_erasing_regions(goal={:#?})", goal);
+
+            tcx.sess
+                .perf_stats
+                .normalize_generic_arg_after_erasing_regions
+                .fetch_add(1, Ordering::Relaxed);
+            normalize_after_erasing_regions(tcx, goal)
+        },
+        normalize_mir_const_after_erasing_regions: |tcx, goal| {
+            normalize_after_erasing_regions(tcx, goal)
+        },
+        ..*p
+    };
 }
 
-fn normalize_generic_arg_after_erasing_regions<'tcx>(
+#[instrument(level = "debug", skip(tcx))]
+fn normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Copy>(
     tcx: TyCtxt<'tcx>,
-    goal: ParamEnvAnd<'tcx, GenericArg<'tcx>>,
-) -> GenericArg<'tcx> {
-    debug!("normalize_generic_arg_after_erasing_regions(goal={:#?})", goal);
-
+    goal: ParamEnvAnd<'tcx, T>,
+) -> T {
     let ParamEnvAnd { param_env, value } = goal;
-    tcx.sess.perf_stats.normalize_generic_arg_after_erasing_regions.fetch_add(1, Ordering::Relaxed);
     tcx.infer_ctxt().enter(|infcx| {
         let cause = ObligationCause::dummy();
         match infcx.at(&cause, param_env).normalize(value) {

src/test/ui/associated-consts/defaults-cyclic-fail.rs

 // build-fail
-//~^ ERROR cycle detected when normalizing `<() as Tr>::A`
+//~^ ERROR cycle detected when normalizing
 
 // Cyclic assoc. const defaults don't error unless *used*
 trait Tr {

src/test/ui/consts/const-eval/conditional_array_execution.rs

@@ -10,7 +10,7 @@
 
 fn main() {
     println!("{}", FOO);
-    //~^ ERROR
+    //~^ ERROR evaluation of constant value failed
     //~| WARN erroneous constant used [const_err]
     //~| WARN this was previously accepted by the compiler but is being phased out
 }

src/test/ui/consts/const-eval/const-eval-query-stack.rs

-//~ERROR constructed but no error reported
-// compile-flags: -Ztreat-err-as-bug=2
+// compile-flags: -Ztreat-err-as-bug=1
 // build-fail
 // failure-status: 101
 // rustc-env:RUST_BACKTRACE=1

src/test/ui/consts/const-eval/const-eval-query-stack.stderr

 warning: any use of this value will cause an error
-  --> $DIR/const-eval-query-stack.rs:20:16
+  --> $DIR/const-eval-query-stack.rs:19:16
    |
 LL | const X: i32 = 1 / 0;
    | ---------------^^^^^-
@@ -7,7 +7,7 @@ LL | const X: i32 = 1 / 0;
    |                attempt to divide `1_i32` by zero
    |
 note: the lint level is defined here
-  --> $DIR/const-eval-query-stack.rs:19:8
+  --> $DIR/const-eval-query-stack.rs:18:8
    |
 LL | #[warn(const_err)]
    |        ^^^^^^^^^
@@ -15,12 +15,16 @@ LL | #[warn(const_err)]
    = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
 
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const-eval-query-stack.rs:24:28
+  --> $DIR/const-eval-query-stack.rs:23:28
    |
 LL |     let x: &'static i32 = &X;
    |                            ^ referenced constant has errors
+
 query stack during panic:
-#0 [normalize_generic_arg_after_erasing_regions] normalizing `main::promoted[1]`
-#1 [optimized_mir] optimizing MIR for `main`
-#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
+#0 [eval_to_allocation_raw] const-evaluating + checking `main::promoted[1]`
+#1 [eval_to_const_value_raw] simplifying constant for the type system `main::promoted[1]`
+#2 [eval_to_const_value_raw] simplifying constant for the type system `main::promoted[1]`
+#3 [normalize_mir_const_after_erasing_regions] normalizing `main::promoted[1]`
+#4 [optimized_mir] optimizing MIR for `main`
+#5 [collect_and_partition_mono_items] collect_and_partition_mono_items
 end of query stack

src/test/ui/consts/const-eval/issue-44578.rs

@@ -25,5 +25,5 @@ impl Foo for u16 {
 
 fn main() {
     println!("{}", <Bar<u16, u8> as Foo>::AMT);
-    //~^ ERROR evaluation of constant value failed [E0080]
+    //~^ ERROR evaluation of constant value failed
 }

src/test/ui/suggestions/lifetimes/missing-lifetimes-in-signature.nll.stderr

-error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/missing-lifetimes-in-signature.rs:36:11
-   |
-LL | fn baz<G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
-   |        -  ^^ undeclared lifetime
-   |        |
-   |        help: consider introducing lifetime `'a` here: `'a,`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0261`.