Auto merge of #135286 - matthiaskrgr:rollup-sxuq1nh, r=matthiaskrgr

Rollup of 3 pull requests

Successful merges:

 - #134898 (Make it easier to run CI jobs locally)
 - #135195 (Make `lit_to_mir_constant` and `lit_to_const` infallible)
 - #135261 (Account for identity substituted items in symbol mangling)

r? `@ghost`
`@rustbot` modify labels: rollup

11 files changed, 130 insertions, 144 deletions

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 0a41dad0dd8..cb90fff782f 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -35,7 +35,7 @@ use rustc_hir::{self as hir, AnonConst, GenericArg, GenericArgs, HirId};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::middle::stability::AllowUnstable;
-use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
+use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::ty::fold::fold_regions;
 use rustc_middle::ty::print::PrintPolyTraitRefExt as _;
 use rustc_middle::ty::{
@@ -2262,25 +2262,11 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             _ => None,
         };
 
-        if let Some(lit_input) = lit_input {
-            // If an error occurred, ignore that it's a literal and leave reporting the error up to
-            // mir.
-            match tcx.at(expr.span).lit_to_const(lit_input) {
-                Ok(c) => return Some(c),
-                Err(_) if lit_input.ty.has_aliases() => {
-                    // allow the `ty` to be an alias type, though we cannot handle it here
-                    return None;
-                }
-                Err(e) => {
-                    tcx.dcx().span_delayed_bug(
-                        expr.span,
-                        format!("try_lower_anon_const_lit: couldn't lit_to_const {e:?}"),
-                    );
-                }
-            }
-        }
-
-        None
+        lit_input
+            // Allow the `ty` to be an alias type, though we cannot handle it here, we just go through
+            // the more expensive anon const code path.
+            .filter(|l| !l.ty.has_aliases())
+            .map(|l| tcx.at(expr.span).lit_to_const(l))
     }
 
     fn lower_delegation_ty(&self, idx: hir::InferDelegationKind) -> Ty<'tcx> {
@@ -2454,13 +2440,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                                 hir::PatExprKind::Lit { lit, negated } => {
                                     let lit_input =
                                         LitToConstInput { lit: &lit.node, ty, neg: negated };
-                                    let ct = match tcx.lit_to_const(lit_input) {
-                                        Ok(c) => c,
-                                        Err(LitToConstError::Reported(err)) => {
-                                            ty::Const::new_error(tcx, err)
-                                        }
-                                        Err(LitToConstError::TypeError) => todo!(),
-                                    };
+                                    let ct = tcx.lit_to_const(lit_input);
                                     (ct, ty)
                                 }
 
diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs
index 8d73c9e76de..b88137544bc 100644
--- a/compiler/rustc_middle/src/mir/interpret/mod.rs
+++ b/compiler/rustc_middle/src/mir/interpret/mod.rs
@@ -16,7 +16,6 @@ use rustc_abi::{AddressSpace, Align, Endian, HasDataLayout, Size};
 use rustc_ast::{LitKind, Mutability};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lock;
-use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
@@ -84,16 +83,6 @@ pub struct LitToConstInput<'tcx> {
     pub neg: bool,
 }
 
-/// Error type for `tcx.lit_to_const`.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable)]
-pub enum LitToConstError {
-    /// The literal's inferred type did not match the expected `ty` in the input.
-    /// This is used for graceful error handling (`span_delayed_bug`) in
-    /// type checking (`Const::from_anon_const`).
-    TypeError,
-    Reported(ErrorGuaranteed),
-}
-
 #[derive(Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct AllocId(pub NonZero<u64>);
 
diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index b72c0e776fe..1676afb4b6e 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -141,14 +141,6 @@ impl EraseType for Result<rustc_abi::TyAndLayout<'_, Ty<'_>>, &ty::layout::Layou
     >()];
 }
 
-impl EraseType for Result<ty::Const<'_>, mir::interpret::LitToConstError> {
-    type Result = [u8; size_of::<Result<ty::Const<'static>, mir::interpret::LitToConstError>>()];
-}
-
-impl EraseType for Result<mir::Const<'_>, mir::interpret::LitToConstError> {
-    type Result = [u8; size_of::<Result<mir::Const<'static>, mir::interpret::LitToConstError>>()];
-}
-
 impl EraseType for Result<mir::ConstAlloc<'_>, mir::interpret::ErrorHandled> {
     type Result = [u8; size_of::<Result<mir::ConstAlloc<'static>, mir::interpret::ErrorHandled>>()];
 }
@@ -296,7 +288,6 @@ trivial! {
     rustc_middle::mir::interpret::AllocId,
     rustc_middle::mir::interpret::CtfeProvenance,
     rustc_middle::mir::interpret::ErrorHandled,
-    rustc_middle::mir::interpret::LitToConstError,
     rustc_middle::thir::ExprId,
     rustc_middle::traits::CodegenObligationError,
     rustc_middle::traits::EvaluationResult,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 95995b956cd..283675573d4 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -57,7 +57,7 @@ use crate::middle::resolve_bound_vars::{ObjectLifetimeDefault, ResolveBoundVars,
 use crate::middle::stability::{self, DeprecationEntry};
 use crate::mir::interpret::{
     EvalStaticInitializerRawResult, EvalToAllocationRawResult, EvalToConstValueResult,
-    EvalToValTreeResult, GlobalId, LitToConstError, LitToConstInput,
+    EvalToValTreeResult, GlobalId, LitToConstInput,
 };
 use crate::mir::mono::{CodegenUnit, CollectionMode, MonoItem};
 use crate::query::erase::{Erase, erase, restore};
@@ -1268,7 +1268,7 @@ rustc_queries! {
     // FIXME get rid of this with valtrees
     query lit_to_const(
         key: LitToConstInput<'tcx>
-    ) -> Result<ty::Const<'tcx>, LitToConstError> {
+    ) -> ty::Const<'tcx> {
         desc { "converting literal to const" }
     }
 
diff --git a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
index f611b69905c..e86e01451fe 100644
--- a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
+++ b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
@@ -165,10 +165,14 @@ impl<'tcx> NormalizeAfterErasingRegionsFolder<'tcx> {
         arg: ty::GenericArg<'tcx>,
     ) -> ty::GenericArg<'tcx> {
         let arg = self.typing_env.as_query_input(arg);
-        self.tcx.try_normalize_generic_arg_after_erasing_regions(arg).unwrap_or_else(|_| bug!(
-            "Failed to normalize {:?}, maybe try to call `try_normalize_erasing_regions` instead",
-            arg.value
-        ))
+        self.tcx.try_normalize_generic_arg_after_erasing_regions(arg).unwrap_or_else(|_| {
+            bug!(
+                "Failed to normalize {:?} in typing_env={:?}, \
+                maybe try to call `try_normalize_erasing_regions` instead",
+                arg.value,
+                self.typing_env,
+            )
+        })
     }
 }
 
diff --git a/compiler/rustc_mir_build/src/builder/expr/as_constant.rs b/compiler/rustc_mir_build/src/builder/expr/as_constant.rs
index 177c1e33a83..e4e452aff75 100644
--- a/compiler/rustc_mir_build/src/builder/expr/as_constant.rs
+++ b/compiler/rustc_mir_build/src/builder/expr/as_constant.rs
@@ -3,13 +3,12 @@
 use rustc_abi::Size;
 use rustc_ast as ast;
 use rustc_hir::LangItem;
-use rustc_middle::mir::interpret::{
-    Allocation, CTFE_ALLOC_SALT, LitToConstError, LitToConstInput, Scalar,
-};
+use rustc_middle::mir::interpret::{Allocation, CTFE_ALLOC_SALT, LitToConstInput, Scalar};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty::{
-    self, CanonicalUserType, CanonicalUserTypeAnnotation, Ty, TyCtxt, UserTypeAnnotationIndex,
+    self, CanonicalUserType, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypeVisitableExt as _,
+    UserTypeAnnotationIndex,
 };
 use rustc_middle::{bug, mir, span_bug};
 use tracing::{instrument, trace};
@@ -50,16 +49,7 @@ pub(crate) fn as_constant_inner<'tcx>(
     let Expr { ty, temp_lifetime: _, span, ref kind } = *expr;
     match *kind {
         ExprKind::Literal { lit, neg } => {
-            let const_ = match lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg })
-            {
-                Ok(c) => c,
-                Err(LitToConstError::Reported(guar)) => {
-                    Const::Ty(Ty::new_error(tcx, guar), ty::Const::new_error(tcx, guar))
-                }
-                Err(LitToConstError::TypeError) => {
-                    bug!("encountered type error in `lit_to_mir_constant`")
-                }
-            };
+            let const_ = lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg });
 
             ConstOperand { span, user_ty: None, const_ }
         }
@@ -108,11 +98,13 @@ pub(crate) fn as_constant_inner<'tcx>(
 }
 
 #[instrument(skip(tcx, lit_input))]
-fn lit_to_mir_constant<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    lit_input: LitToConstInput<'tcx>,
-) -> Result<Const<'tcx>, LitToConstError> {
+fn lit_to_mir_constant<'tcx>(tcx: TyCtxt<'tcx>, lit_input: LitToConstInput<'tcx>) -> Const<'tcx> {
     let LitToConstInput { lit, ty, neg } = lit_input;
+
+    if let Err(guar) = ty.error_reported() {
+        return Const::Ty(Ty::new_error(tcx, guar), ty::Const::new_error(tcx, guar));
+    }
+
     let trunc = |n| {
         let width = match tcx.layout_of(ty::TypingEnv::fully_monomorphized().as_query_input(ty)) {
             Ok(layout) => layout.size,
@@ -123,7 +115,7 @@ fn lit_to_mir_constant<'tcx>(
         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
         let result = width.truncate(n);
         trace!("trunc result: {}", result);
-        Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
+        ConstValue::Scalar(Scalar::from_uint(result, width))
     };
 
     let value = match (lit, ty.kind()) {
@@ -154,20 +146,18 @@ fn lit_to_mir_constant<'tcx>(
             ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
         }
         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
-            trunc(if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() })?
-        }
-        (ast::LitKind::Float(n, _), ty::Float(fty)) => parse_float_into_constval(*n, *fty, neg)
-            .ok_or_else(|| {
-                LitToConstError::Reported(
-                    tcx.dcx()
-                        .delayed_bug(format!("couldn't parse float literal: {:?}", lit_input.lit)),
-                )
-            })?,
+            trunc(if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() })
+        }
+        (ast::LitKind::Float(n, _), ty::Float(fty)) => {
+            parse_float_into_constval(*n, *fty, neg).unwrap()
+        }
         (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
         (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
-        (ast::LitKind::Err(guar), _) => return Err(LitToConstError::Reported(*guar)),
-        _ => return Err(LitToConstError::TypeError),
+        (ast::LitKind::Err(guar), _) => {
+            return Const::Ty(Ty::new_error(tcx, *guar), ty::Const::new_error(tcx, *guar));
+        }
+        _ => bug!("invalid lit/ty combination in `lit_to_mir_constant`: {lit:?}: {ty:?}"),
     };
 
-    Ok(Const::Val(value, ty))
+    Const::Val(value, ty)
 }
diff --git a/compiler/rustc_mir_build/src/thir/constant.rs b/compiler/rustc_mir_build/src/thir/constant.rs
index ce1c635d1b9..49db522cf0e 100644
--- a/compiler/rustc_mir_build/src/thir/constant.rs
+++ b/compiler/rustc_mir_build/src/thir/constant.rs
@@ -1,7 +1,7 @@
 use rustc_ast as ast;
 use rustc_hir::LangItem;
 use rustc_middle::bug;
-use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
+use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::ty::{self, ScalarInt, TyCtxt, TypeVisitableExt as _};
 use tracing::trace;
 
@@ -10,11 +10,11 @@ use crate::builder::parse_float_into_scalar;
 pub(crate) fn lit_to_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     lit_input: LitToConstInput<'tcx>,
-) -> Result<ty::Const<'tcx>, LitToConstError> {
+) -> ty::Const<'tcx> {
     let LitToConstInput { lit, ty, neg } = lit_input;
 
     if let Err(guar) = ty.error_reported() {
-        return Ok(ty::Const::new_error(tcx, guar));
+        return ty::Const::new_error(tcx, guar);
     }
 
     let trunc = |n| {
@@ -28,8 +28,8 @@ pub(crate) fn lit_to_const<'tcx>(
         let result = width.truncate(n);
         trace!("trunc result: {}", result);
 
-        Ok(ScalarInt::try_from_uint(result, width)
-            .unwrap_or_else(|| bug!("expected to create ScalarInt from uint {:?}", result)))
+        ScalarInt::try_from_uint(result, width)
+            .unwrap_or_else(|| bug!("expected to create ScalarInt from uint {:?}", result))
     };
 
     let valtree = match (lit, ty.kind()) {
@@ -57,20 +57,20 @@ pub(crate) fn lit_to_const<'tcx>(
         }
         (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
             let scalar_int =
-                trunc(if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() })?;
+                trunc(if neg { (n.get() as i128).overflowing_neg().0 as u128 } else { n.get() });
             ty::ValTree::from_scalar_int(scalar_int)
         }
         (ast::LitKind::Bool(b), ty::Bool) => ty::ValTree::from_scalar_int((*b).into()),
         (ast::LitKind::Float(n, _), ty::Float(fty)) => {
-            let bits = parse_float_into_scalar(*n, *fty, neg).ok_or_else(|| {
+            let bits = parse_float_into_scalar(*n, *fty, neg).unwrap_or_else(|| {
                 tcx.dcx().bug(format!("couldn't parse float literal: {:?}", lit_input.lit))
-            })?;
+            });
             ty::ValTree::from_scalar_int(bits)
         }
         (ast::LitKind::Char(c), ty::Char) => ty::ValTree::from_scalar_int((*c).into()),
-        (ast::LitKind::Err(guar), _) => return Err(LitToConstError::Reported(*guar)),
-        _ => return Err(LitToConstError::TypeError),
+        (ast::LitKind::Err(guar), _) => return ty::Const::new_error(tcx, *guar),
+        _ => return ty::Const::new_misc_error(tcx),
     };
 
-    Ok(ty::Const::new_value(tcx, valtree, ty))
+    ty::Const::new_value(tcx, valtree, ty)
 }
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 242b62dfa8d..44b038bb5fa 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -13,7 +13,7 @@ use rustc_hir::pat_util::EnumerateAndAdjustIterator;
 use rustc_hir::{self as hir, ByRef, Mutability, RangeEnd};
 use rustc_index::Idx;
 use rustc_lint as lint;
-use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
+use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::thir::{
     Ascription, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
 };
@@ -669,11 +669,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         let ct_ty = self.typeck_results.node_type(expr.hir_id);
         let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg };
-        match self.tcx.at(expr.span).lit_to_const(lit_input) {
-            Ok(constant) => self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind,
-            Err(LitToConstError::Reported(e)) => PatKind::Error(e),
-            Err(LitToConstError::TypeError) => bug!("lower_lit: had type error"),
-        }
+        let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
+        self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
     }
 }
 
diff --git a/compiler/rustc_symbol_mangling/src/legacy.rs b/compiler/rustc_symbol_mangling/src/legacy.rs
index 333ea0214eb..58c0a05df1f 100644
--- a/compiler/rustc_symbol_mangling/src/legacy.rs
+++ b/compiler/rustc_symbol_mangling/src/legacy.rs
@@ -8,7 +8,6 @@ use rustc_middle::bug;
 use rustc_middle::ty::print::{PrettyPrinter, Print, PrintError, Printer};
 use rustc_middle::ty::{
     self, GenericArg, GenericArgKind, Instance, ReifyReason, Ty, TyCtxt, TypeVisitableExt,
-    TypingEnv,
 };
 use tracing::debug;
 
@@ -387,23 +386,44 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
     ) -> Result<(), PrintError> {
         let self_ty = self.tcx.type_of(impl_def_id);
         let impl_trait_ref = self.tcx.impl_trait_ref(impl_def_id);
-        let (typing_env, mut self_ty, mut impl_trait_ref) =
-            if self.tcx.generics_of(impl_def_id).count() <= args.len() {
-                (
-                    TypingEnv::fully_monomorphized(),
-                    self_ty.instantiate(self.tcx, args),
-                    impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate(self.tcx, args)),
-                )
-            } else {
-                // We are probably printing a nested item inside of an impl.
-                // Use the identity substitutions for the impl. We also need
-                // a well-formed param-env, so let's use post-analysis.
-                (
-                    TypingEnv::post_analysis(self.tcx, impl_def_id),
-                    self_ty.instantiate_identity(),
-                    impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate_identity()),
-                )
-            };
+        let generics = self.tcx.generics_of(impl_def_id);
+        // We have two cases to worry about here:
+        // 1. We're printing a nested item inside of an impl item, like an inner
+        // function inside of a method. Due to the way that def path printing works,
+        // we'll render this something like `<Ty as Trait>::method::inner_fn`
+        // but we have no substs for this impl since it's not really inheriting
+        // generics from the outer item. We need to use the identity substs, and
+        // to normalize we need to use the correct param-env too.
+        // 2. We're mangling an item with identity substs. This seems to only happen
+        // when generating coverage, since we try to generate coverage for unused
+        // items too, and if something isn't monomorphized then we necessarily don't
+        // have anything to substitute the instance with.
+        // NOTE: We don't support mangling partially substituted but still polymorphic
+        // instances, like `impl<A> Tr<A> for ()` where `A` is substituted w/ `(T,)`.
+        let (typing_env, mut self_ty, mut impl_trait_ref) = if generics.count() > args.len()
+            || &args[..generics.count()]
+                == self
+                    .tcx
+                    .erase_regions(ty::GenericArgs::identity_for_item(self.tcx, impl_def_id))
+                    .as_slice()
+        {
+            (
+                ty::TypingEnv::post_analysis(self.tcx, impl_def_id),
+                self_ty.instantiate_identity(),
+                impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate_identity()),
+            )
+        } else {
+            assert!(
+                !args.has_non_region_param(),
+                "should not be mangling partially substituted \
+                polymorphic instance: {impl_def_id:?} {args:?}"
+            );
+            (
+                ty::TypingEnv::fully_monomorphized(),
+                self_ty.instantiate(self.tcx, args),
+                impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate(self.tcx, args)),
+            )
+        };
 
         match &mut impl_trait_ref {
             Some(impl_trait_ref) => {
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index b77ad209e2b..4ddf530a00d 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -233,23 +233,44 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
 
         let self_ty = self.tcx.type_of(impl_def_id);
         let impl_trait_ref = self.tcx.impl_trait_ref(impl_def_id);
-        let (typing_env, mut self_ty, mut impl_trait_ref) =
-            if self.tcx.generics_of(impl_def_id).count() <= args.len() {
-                (
-                    ty::TypingEnv::fully_monomorphized(),
-                    self_ty.instantiate(self.tcx, args),
-                    impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate(self.tcx, args)),
-                )
-            } else {
-                // We are probably printing a nested item inside of an impl.
-                // Use the identity substitutions for the impl. We also need
-                // a well-formed param-env, so let's use post-analysis.
-                (
-                    ty::TypingEnv::post_analysis(self.tcx, impl_def_id),
-                    self_ty.instantiate_identity(),
-                    impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate_identity()),
-                )
-            };
+        let generics = self.tcx.generics_of(impl_def_id);
+        // We have two cases to worry about here:
+        // 1. We're printing a nested item inside of an impl item, like an inner
+        // function inside of a method. Due to the way that def path printing works,
+        // we'll render this something like `<Ty as Trait>::method::inner_fn`
+        // but we have no substs for this impl since it's not really inheriting
+        // generics from the outer item. We need to use the identity substs, and
+        // to normalize we need to use the correct param-env too.
+        // 2. We're mangling an item with identity substs. This seems to only happen
+        // when generating coverage, since we try to generate coverage for unused
+        // items too, and if something isn't monomorphized then we necessarily don't
+        // have anything to substitute the instance with.
+        // NOTE: We don't support mangling partially substituted but still polymorphic
+        // instances, like `impl<A> Tr<A> for ()` where `A` is substituted w/ `(T,)`.
+        let (typing_env, mut self_ty, mut impl_trait_ref) = if generics.count() > args.len()
+            || &args[..generics.count()]
+                == self
+                    .tcx
+                    .erase_regions(ty::GenericArgs::identity_for_item(self.tcx, impl_def_id))
+                    .as_slice()
+        {
+            (
+                ty::TypingEnv::post_analysis(self.tcx, impl_def_id),
+                self_ty.instantiate_identity(),
+                impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate_identity()),
+            )
+        } else {
+            assert!(
+                !args.has_non_region_param(),
+                "should not be mangling partially substituted \
+                polymorphic instance: {impl_def_id:?} {args:?}"
+            );
+            (
+                ty::TypingEnv::fully_monomorphized(),
+                self_ty.instantiate(self.tcx, args),
+                impl_trait_ref.map(|impl_trait_ref| impl_trait_ref.instantiate(self.tcx, args)),
+            )
+        };
 
         match &mut impl_trait_ref {
             Some(impl_trait_ref) => {
diff --git a/compiler/rustc_ty_utils/src/consts.rs b/compiler/rustc_ty_utils/src/consts.rs
index 637e239a570..51a7c976f60 100644
--- a/compiler/rustc_ty_utils/src/consts.rs
+++ b/compiler/rustc_ty_utils/src/consts.rs
@@ -4,7 +4,7 @@ use rustc_abi::{FIRST_VARIANT, VariantIdx};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
-use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
+use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::query::Providers;
 use rustc_middle::thir::visit;
 use rustc_middle::thir::visit::Visitor;
@@ -118,13 +118,7 @@ fn recurse_build<'tcx>(
         }
         &ExprKind::Literal { lit, neg } => {
             let sp = node.span;
-            match tcx.at(sp).lit_to_const(LitToConstInput { lit: &lit.node, ty: node.ty, neg }) {
-                Ok(c) => c,
-                Err(LitToConstError::Reported(guar)) => ty::Const::new_error(tcx, guar),
-                Err(LitToConstError::TypeError) => {
-                    bug!("encountered type error in lit_to_const")
-                }
-            }
+            tcx.at(sp).lit_to_const(LitToConstInput { lit: &lit.node, ty: node.ty, neg })
         }
         &ExprKind::NonHirLiteral { lit, user_ty: _ } => {
             let val = ty::ValTree::from_scalar_int(lit);