Auto merge of #131226 - nnethercote:rustc_infer-cleanups, r=lcnr

`rustc_infer` cleanups

Various small improvements I found while reading over this code.

r? `@lcnr`

compiler/rustc_errors/src/lib.rs

@@ -925,18 +925,6 @@ impl<'a> DiagCtxtHandle<'a> {
         self.inner.borrow_mut().emit_stashed_diagnostics()
     }
 
-    /// This excludes lint errors, and delayed bugs.
-    #[inline]
-    pub fn err_count_excluding_lint_errs(&self) -> usize {
-        let inner = self.inner.borrow();
-        inner.err_guars.len()
-            + inner
-                .stashed_diagnostics
-                .values()
-                .filter(|(diag, guar)| guar.is_some() && diag.is_lint.is_none())
-                .count()
-    }
-
     /// This excludes delayed bugs.
     #[inline]
     pub fn err_count(&self) -> usize {

compiler/rustc_infer/src/infer/at.rs

@@ -82,7 +82,6 @@ impl<'tcx> InferCtxt<'tcx> {
             reported_trait_errors: self.reported_trait_errors.clone(),
             reported_signature_mismatch: self.reported_signature_mismatch.clone(),
             tainted_by_errors: self.tainted_by_errors.clone(),
-            err_count_on_creation: self.err_count_on_creation,
             universe: self.universe.clone(),
             intercrate,
             next_trait_solver: self.next_trait_solver,
@@ -382,21 +381,7 @@ impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
                 (GenericArgKind::Const(a), GenericArgKind::Const(b)) => {
                     ValuePairs::Terms(ExpectedFound::new(true, a.into(), b.into()))
                 }
-
+                _ => bug!("relating different kinds: {a:?} {b:?}"),
-                (
-                    GenericArgKind::Lifetime(_),
-                    GenericArgKind::Type(_) | GenericArgKind::Const(_),
-                )
-                | (
-                    GenericArgKind::Type(_),
-                    GenericArgKind::Lifetime(_) | GenericArgKind::Const(_),
-                )
-                | (
-                    GenericArgKind::Const(_),
-                    GenericArgKind::Lifetime(_) | GenericArgKind::Type(_),
-                ) => {
-                    bug!("relating different kinds: {a:?} {b:?}")
-                }
             },
         }
     }

compiler/rustc_infer/src/infer/mod.rs

@@ -14,7 +14,8 @@ use region_constraints::{
     GenericKind, RegionConstraintCollector, RegionConstraintStorage, VarInfos, VerifyBound,
 };
 pub use relate::StructurallyRelateAliases;
-pub use relate::combine::{CombineFields, PredicateEmittingRelation};
+use relate::combine::CombineFields;
+pub use relate::combine::PredicateEmittingRelation;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::sync::Lrc;
@@ -50,23 +51,22 @@ use snapshot::undo_log::InferCtxtUndoLogs;
 use tracing::{debug, instrument};
 use type_variable::TypeVariableOrigin;
 
-use crate::infer::relate::RelateResult;
 use crate::traits::{self, ObligationCause, ObligationInspector, PredicateObligation, TraitEngine};
 
 pub mod at;
 pub mod canonical;
 mod context;
-pub mod free_regions;
+mod free_regions;
 mod freshen;
 mod lexical_region_resolve;
-pub mod opaque_types;
+mod opaque_types;
 pub mod outlives;
 mod projection;
 pub mod region_constraints;
 pub mod relate;
 pub mod resolve;
 pub(crate) mod snapshot;
-pub mod type_variable;
+mod type_variable;
 
 #[must_use]
 #[derive(Debug)]
@@ -76,8 +76,7 @@ pub struct InferOk<'tcx, T> {
 }
 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
 
-pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
+pub(crate) type FixupResult<T> = Result<T, FixupError>; // "fixup result"
-pub type FixupResult<T> = Result<T, FixupError>; // "fixup result"
 
 pub(crate) type UnificationTable<'a, 'tcx, T> = ut::UnificationTable<
     ut::InPlace<T, &'a mut ut::UnificationStorage<T>, &'a mut InferCtxtUndoLogs<'tcx>>,
@@ -202,7 +201,7 @@ impl<'tcx> InferCtxtInner<'tcx> {
     }
 
     #[inline]
-    pub fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
+    fn opaque_types(&mut self) -> opaque_types::OpaqueTypeTable<'_, 'tcx> {
         self.opaque_type_storage.with_log(&mut self.undo_log)
     }
 
@@ -280,27 +279,14 @@ pub struct InferCtxt<'tcx> {
     pub reported_signature_mismatch: RefCell<FxHashSet<(Span, Option<Span>)>>,
 
     /// When an error occurs, we want to avoid reporting "derived"
-    /// errors that are due to this original failure. Normally, we
+    /// errors that are due to this original failure. We have this
-    /// handle this with the `err_count_on_creation` count, which
+    /// flag that one can set whenever one creates a type-error that
-    /// basically just tracks how many errors were reported when we
+    /// is due to an error in a prior pass.
-    /// started type-checking a fn and checks to see if any new errors
-    /// have been reported since then. Not great, but it works.
-    ///
-    /// However, when errors originated in other passes -- notably
-    /// resolve -- this heuristic breaks down. Therefore, we have this
-    /// auxiliary flag that one can set whenever one creates a
-    /// type-error that is due to an error in a prior pass.
     ///
     /// Don't read this flag directly, call `is_tainted_by_errors()`
     /// and `set_tainted_by_errors()`.
     tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
 
-    /// Track how many errors were reported when this infcx is created.
-    /// If the number of errors increases, that's also a sign (like
-    /// `tainted_by_errors`) to avoid reporting certain kinds of errors.
-    // FIXME(matthewjasper) Merge into `tainted_by_errors`
-    err_count_on_creation: usize,
-
     /// What is the innermost universe we have created? Starts out as
     /// `UniverseIndex::root()` but grows from there as we enter
     /// universal quantifiers.
@@ -509,14 +495,31 @@ pub enum NllRegionVariableOrigin {
     },
 }
 
-// FIXME(eddyb) investigate overlap between this and `TyOrConstInferVar`.
 #[derive(Copy, Clone, Debug)]
-pub enum FixupError {
+pub struct FixupError {
-    UnresolvedIntTy(IntVid),
+    unresolved: TyOrConstInferVar,
-    UnresolvedFloatTy(FloatVid),
+}
-    UnresolvedTy(TyVid),
+
-    UnresolvedConst(ConstVid),
+impl fmt::Display for FixupError {
-    UnresolvedEffect(EffectVid),
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use TyOrConstInferVar::*;
+
+        match self.unresolved {
+            TyInt(_) => write!(
+                f,
+                "cannot determine the type of this integer; \
+                 add a suffix to specify the type explicitly"
+            ),
+            TyFloat(_) => write!(
+                f,
+                "cannot determine the type of this number; \
+                 add a suffix to specify the type explicitly"
+            ),
+            Ty(_) => write!(f, "unconstrained type"),
+            Const(_) => write!(f, "unconstrained const value"),
+            Effect(_) => write!(f, "unconstrained effect value"),
+        }
+    }
 }
 
 /// See the `region_obligations` field for more information.
@@ -527,28 +530,6 @@ pub struct RegionObligation<'tcx> {
     pub origin: SubregionOrigin<'tcx>,
 }
 
-impl fmt::Display for FixupError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        use self::FixupError::*;
-
-        match *self {
-            UnresolvedIntTy(_) => write!(
-                f,
-                "cannot determine the type of this integer; \
-                 add a suffix to specify the type explicitly"
-            ),
-            UnresolvedFloatTy(_) => write!(
-                f,
-                "cannot determine the type of this number; \
-                 add a suffix to specify the type explicitly"
-            ),
-            UnresolvedTy(_) => write!(f, "unconstrained type"),
-            UnresolvedConst(_) => write!(f, "unconstrained const value"),
-            UnresolvedEffect(_) => write!(f, "unconstrained effect value"),
-        }
-    }
-}
-
 /// Used to configure inference contexts before their creation.
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
@@ -588,14 +569,6 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
         self
     }
 
-    pub fn with_defining_opaque_types(
-        mut self,
-        defining_opaque_types: &'tcx ty::List<LocalDefId>,
-    ) -> Self {
-        self.defining_opaque_types = defining_opaque_types;
-        self
-    }
-
     pub fn with_next_trait_solver(mut self, next_trait_solver: bool) -> Self {
         self.next_trait_solver = next_trait_solver;
         self
@@ -624,14 +597,15 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// the bound values in `C` to their instantiated values in `V`
     /// (in other words, `S(C) = V`).
     pub fn build_with_canonical<T>(
-        self,
+        mut self,
         span: Span,
         canonical: &Canonical<'tcx, T>,
     ) -> (InferCtxt<'tcx>, T, CanonicalVarValues<'tcx>)
     where
         T: TypeFoldable<TyCtxt<'tcx>>,
     {
-        let infcx = self.with_defining_opaque_types(canonical.defining_opaque_types).build();
+        self.defining_opaque_types = canonical.defining_opaque_types;
+        let infcx = self.build();
         let (value, args) = infcx.instantiate_canonical(span, canonical);
         (infcx, value, args)
     }
@@ -657,7 +631,6 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             reported_trait_errors: Default::default(),
             reported_signature_mismatch: Default::default(),
             tainted_by_errors: Cell::new(None),
-            err_count_on_creation: tcx.dcx().err_count_excluding_lint_errs(),
             universe: Cell::new(ty::UniverseIndex::ROOT),
             intercrate,
             next_trait_solver,
@@ -919,28 +892,16 @@ impl<'tcx> InferCtxt<'tcx> {
         ty::Const::new_var(self.tcx, vid)
     }
 
-    pub fn next_const_var_id(&self, origin: ConstVariableOrigin) -> ConstVid {
-        self.inner
-            .borrow_mut()
-            .const_unification_table()
-            .new_key(ConstVariableValue::Unknown { origin, universe: self.universe() })
-            .vid
-    }
-
-    fn next_int_var_id(&self) -> IntVid {
-        self.inner.borrow_mut().int_unification_table().new_key(ty::IntVarValue::Unknown)
-    }
-
     pub fn next_int_var(&self) -> Ty<'tcx> {
-        Ty::new_int_var(self.tcx, self.next_int_var_id())
+        let next_int_var_id =
-    }
+            self.inner.borrow_mut().int_unification_table().new_key(ty::IntVarValue::Unknown);
-
+        Ty::new_int_var(self.tcx, next_int_var_id)
-    fn next_float_var_id(&self) -> FloatVid {
-        self.inner.borrow_mut().float_unification_table().new_key(ty::FloatVarValue::Unknown)
     }
 
     pub fn next_float_var(&self) -> Ty<'tcx> {
-        Ty::new_float_var(self.tcx, self.next_float_var_id())
+        let next_float_var_id =
+            self.inner.borrow_mut().float_unification_table().new_key(ty::FloatVarValue::Unknown);
+        Ty::new_float_var(self.tcx, next_float_var_id)
     }
 
     /// Creates a fresh region variable with the next available index.
@@ -1353,7 +1314,7 @@ impl<'tcx> InferCtxt<'tcx> {
     }
 
     /// See the [`region_constraints::RegionConstraintCollector::verify_generic_bound`] method.
-    pub fn verify_generic_bound(
+    pub(crate) fn verify_generic_bound(
         &self,
         origin: SubregionOrigin<'tcx>,
         kind: GenericKind<'tcx>,

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

@@ -13,16 +13,15 @@ use rustc_middle::ty::{
 use rustc_span::Span;
 use tracing::{debug, instrument};
 
+use super::DefineOpaqueTypes;
 use crate::errors::OpaqueHiddenTypeDiag;
 use crate::infer::{InferCtxt, InferOk};
 use crate::traits::{self, Obligation};
 
 mod table;
 
-pub type OpaqueTypeMap<'tcx> = FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueTypeDecl<'tcx>>;
+pub(crate) type OpaqueTypeMap<'tcx> = FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueTypeDecl<'tcx>>;
-pub use table::{OpaqueTypeStorage, OpaqueTypeTable};
+pub(crate) use table::{OpaqueTypeStorage, OpaqueTypeTable};
-
-use super::DefineOpaqueTypes;
 
 /// Information about the opaque types whose values we
 /// are inferring in this function (these are the `impl Trait` that
@@ -377,9 +376,9 @@ impl<'tcx> InferCtxt<'tcx> {
 ///
 /// We ignore any type parameters because impl trait values are assumed to
 /// capture all the in-scope type parameters.
-pub struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP: FnMut(ty::Region<'tcx>)> {
+struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP: FnMut(ty::Region<'tcx>)> {
-    pub tcx: TyCtxt<'tcx>,
+    tcx: TyCtxt<'tcx>,
-    pub op: OP,
+    op: OP,
 }
 
 impl<'tcx, OP> TypeVisitor<TyCtxt<'tcx>> for ConstrainOpaqueTypeRegionVisitor<'tcx, OP>
@@ -455,20 +454,6 @@ where
     }
 }
 
-pub enum UseKind {
-    DefiningUse,
-    OpaqueUse,
-}
-
-impl UseKind {
-    pub fn is_defining(self) -> bool {
-        match self {
-            UseKind::DefiningUse => true,
-            UseKind::OpaqueUse => false,
-        }
-    }
-}
-
 impl<'tcx> InferCtxt<'tcx> {
     #[instrument(skip(self), level = "debug")]
     fn register_hidden_type(

compiler/rustc_infer/src/infer/opaque_types/table.rs

@@ -7,7 +7,7 @@ use super::{OpaqueTypeDecl, OpaqueTypeMap};
 use crate::infer::snapshot::undo_log::{InferCtxtUndoLogs, UndoLog};
 
 #[derive(Default, Debug, Clone)]
-pub struct OpaqueTypeStorage<'tcx> {
+pub(crate) struct OpaqueTypeStorage<'tcx> {
     /// Opaque types found in explicit return types and their
     /// associated fresh inference variable. Writeback resolves these
     /// variables to get the concrete type, which can be used to
@@ -46,7 +46,7 @@ impl<'tcx> Drop for OpaqueTypeStorage<'tcx> {
     }
 }
 
-pub struct OpaqueTypeTable<'a, 'tcx> {
+pub(crate) struct OpaqueTypeTable<'a, 'tcx> {
     storage: &'a mut OpaqueTypeStorage<'tcx>,
 
     undo_log: &'a mut InferCtxtUndoLogs<'tcx>,

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

@@ -14,7 +14,7 @@ pub mod env;
 pub mod for_liveness;
 pub mod obligations;
 pub mod test_type_match;
-pub mod verify;
+pub(crate) mod verify;
 
 #[instrument(level = "debug", skip(param_env), ret)]
 pub fn explicit_outlives_bounds<'tcx>(

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -15,7 +15,7 @@ use crate::infer::{GenericKind, VerifyBound};
 /// via a "delegate" of type `D` -- this is usually the `infcx`, which
 /// accrues them into the `region_obligations` code, but for NLL we
 /// use something else.
-pub struct VerifyBoundCx<'cx, 'tcx> {
+pub(crate) struct VerifyBoundCx<'cx, 'tcx> {
     tcx: TyCtxt<'tcx>,
     region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
     /// During borrowck, if there are no outlives bounds on a generic
@@ -28,7 +28,7 @@ pub struct VerifyBoundCx<'cx, 'tcx> {
 }
 
 impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
-    pub fn new(
+    pub(crate) fn new(
         tcx: TyCtxt<'tcx>,
         region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
         implicit_region_bound: Option<ty::Region<'tcx>>,
@@ -38,7 +38,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub fn param_or_placeholder_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
+    pub(crate) fn param_or_placeholder_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
         // Start with anything like `T: 'a` we can scrape from the
         // environment. If the environment contains something like
         // `for<'a> T: 'a`, then we know that `T` outlives everything.
@@ -92,7 +92,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// the clause from the environment only applies if `'0 = 'a`,
     /// which we don't know yet. But we would still include `'b` in
     /// this list.
-    pub fn approx_declared_bounds_from_env(
+    pub(crate) fn approx_declared_bounds_from_env(
         &self,
         alias_ty: ty::AliasTy<'tcx>,
     ) -> Vec<ty::PolyTypeOutlivesPredicate<'tcx>> {
@@ -101,7 +101,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub fn alias_bound(&self, alias_ty: ty::AliasTy<'tcx>) -> VerifyBound<'tcx> {
+    pub(crate) fn alias_bound(&self, alias_ty: ty::AliasTy<'tcx>) -> VerifyBound<'tcx> {
         let alias_ty_as_ty = alias_ty.to_ty(self.tcx);
 
         // Search the env for where clauses like `P: 'a`.
@@ -285,7 +285,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ///
     /// This is for simplicity, and because we are not really smart
     /// enough to cope with such bounds anywhere.
-    pub fn declared_bounds_from_definition(
+    pub(crate) fn declared_bounds_from_definition(
         &self,
         alias_ty: ty::AliasTy<'tcx>,
     ) -> impl Iterator<Item = ty::Region<'tcx>> {

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

@@ -304,7 +304,7 @@ pub struct RegionVariableInfo {
     pub universe: ty::UniverseIndex,
 }
 
-pub struct RegionSnapshot {
+pub(crate) struct RegionSnapshot {
     any_unifications: bool,
 }
 

compiler/rustc_infer/src/infer/relate/combine.rs

@@ -33,7 +33,7 @@ use crate::infer::{DefineOpaqueTypes, InferCtxt, TypeTrace, relate};
 use crate::traits::{Obligation, PredicateObligation};
 
 #[derive(Clone)]
-pub struct CombineFields<'infcx, 'tcx> {
+pub(crate) struct CombineFields<'infcx, 'tcx> {
     pub infcx: &'infcx InferCtxt<'tcx>,
     // Immutable fields
     pub trace: TypeTrace<'tcx>,
@@ -47,7 +47,7 @@ pub struct CombineFields<'infcx, 'tcx> {
 }
 
 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
-    pub fn new(
+    pub(crate) fn new(
         infcx: &'infcx InferCtxt<'tcx>,
         trace: TypeTrace<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
@@ -283,22 +283,22 @@ impl<'tcx> InferCtxt<'tcx> {
 }
 
 impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
-    pub fn tcx(&self) -> TyCtxt<'tcx> {
+    pub(crate) fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
-    pub fn equate<'a>(
+    pub(crate) fn equate<'a>(
         &'a mut self,
         structurally_relate_aliases: StructurallyRelateAliases,
     ) -> TypeRelating<'a, 'infcx, 'tcx> {
         TypeRelating::new(self, structurally_relate_aliases, ty::Invariant)
     }
 
-    pub fn sub<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
+    pub(crate) fn sub<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
         TypeRelating::new(self, StructurallyRelateAliases::No, ty::Covariant)
     }
 
-    pub fn sup<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
+    pub(crate) fn sup<'a>(&'a mut self) -> TypeRelating<'a, 'infcx, 'tcx> {
         TypeRelating::new(self, StructurallyRelateAliases::No, ty::Contravariant)
     }
 
@@ -310,14 +310,14 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         LatticeOp::new(self, LatticeOpKind::Glb)
     }
 
-    pub fn register_obligations(
+    pub(crate) fn register_obligations(
         &mut self,
         obligations: impl IntoIterator<Item = Goal<'tcx, ty::Predicate<'tcx>>>,
     ) {
         self.goals.extend(obligations);
     }
 
-    pub fn register_predicates(
+    pub(crate) fn register_predicates(
         &mut self,
         obligations: impl IntoIterator<Item: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {

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

@@ -5,7 +5,7 @@
 pub use rustc_middle::ty::relate::RelateResult;
 pub use rustc_next_trait_solver::relate::*;
 
-pub use self::combine::{CombineFields, PredicateEmittingRelation};
+pub use self::combine::PredicateEmittingRelation;
 
 #[allow(hidden_glob_reexports)]
 pub(super) mod combine;

compiler/rustc_infer/src/infer/relate/type_relating.rs

@@ -13,7 +13,7 @@ use crate::infer::relate::{PredicateEmittingRelation, StructurallyRelateAliases}
 use crate::infer::{DefineOpaqueTypes, InferCtxt, SubregionOrigin};
 
 /// Enforce that `a` is equal to or a subtype of `b`.
-pub struct TypeRelating<'combine, 'a, 'tcx> {
+pub(crate) struct TypeRelating<'combine, 'a, 'tcx> {
     // Immutable except for the `InferCtxt` and the
     // resulting nested `goals`.
     fields: &'combine mut CombineFields<'a, 'tcx>,
@@ -49,7 +49,7 @@ pub struct TypeRelating<'combine, 'a, 'tcx> {
 }
 
 impl<'combine, 'infcx, 'tcx> TypeRelating<'combine, 'infcx, 'tcx> {
-    pub fn new(
+    pub(crate) fn new(
         f: &'combine mut CombineFields<'infcx, 'tcx>,
         structurally_relate_aliases: StructurallyRelateAliases,
         ambient_variance: ty::Variance,

compiler/rustc_infer/src/infer/resolve.rs

@@ -121,8 +121,6 @@ where
     value.try_fold_with(&mut FullTypeResolver { infcx })
 }
 
-// N.B. This type is not public because the protocol around checking the
-// `err` field is not enforceable otherwise.
 struct FullTypeResolver<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
 }
@@ -138,11 +136,13 @@ impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
         if !t.has_infer() {
             Ok(t) // micro-optimize -- if there is nothing in this type that this fold affects...
         } else {
+            use super::TyOrConstInferVar::*;
+
             let t = self.infcx.shallow_resolve(t);
             match *t.kind() {
-                ty::Infer(ty::TyVar(vid)) => Err(FixupError::UnresolvedTy(vid)),
+                ty::Infer(ty::TyVar(vid)) => Err(FixupError { unresolved: Ty(vid) }),
-                ty::Infer(ty::IntVar(vid)) => Err(FixupError::UnresolvedIntTy(vid)),
+                ty::Infer(ty::IntVar(vid)) => Err(FixupError { unresolved: TyInt(vid) }),
-                ty::Infer(ty::FloatVar(vid)) => Err(FixupError::UnresolvedFloatTy(vid)),
+                ty::Infer(ty::FloatVar(vid)) => Err(FixupError { unresolved: TyFloat(vid) }),
                 ty::Infer(_) => {
                     bug!("Unexpected type in full type resolver: {:?}", t);
                 }
@@ -171,13 +171,13 @@ impl<'a, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for FullTypeResolver<'a, 'tcx> {
             let c = self.infcx.shallow_resolve_const(c);
             match c.kind() {
                 ty::ConstKind::Infer(InferConst::Var(vid)) => {
-                    return Err(FixupError::UnresolvedConst(vid));
+                    return Err(FixupError { unresolved: super::TyOrConstInferVar::Const(vid) });
                 }
                 ty::ConstKind::Infer(InferConst::Fresh(_)) => {
                     bug!("Unexpected const in full const resolver: {:?}", c);
                 }
                 ty::ConstKind::Infer(InferConst::EffectVar(evid)) => {
-                    return Err(FixupError::UnresolvedEffect(evid));
+                    return Err(FixupError { unresolved: super::TyOrConstInferVar::Effect(evid) });
                 }
                 _ => {}
             }

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

@@ -5,7 +5,7 @@ use tracing::{debug, instrument};
 use super::InferCtxt;
 use super::region_constraints::RegionSnapshot;
 
-mod fudge;
+pub(crate) mod fudge;
 pub(crate) mod undo_log;
 
 use undo_log::{Snapshot, UndoLog};

compiler/rustc_infer/src/infer/type_variable.rs

@@ -20,7 +20,7 @@ impl<'tcx> Rollback<sv::UndoLog<ut::Delegate<TyVidEqKey<'tcx>>>> for TypeVariabl
 }
 
 #[derive(Clone)]
-pub struct TypeVariableStorage<'tcx> {
+pub(crate) struct TypeVariableStorage<'tcx> {
     /// The origins of each type variable.
     values: IndexVec<TyVid, TypeVariableData>,
     /// Two variables are unified in `eq_relations` when we have a
@@ -29,7 +29,7 @@ pub struct TypeVariableStorage<'tcx> {
     eq_relations: ut::UnificationTableStorage<TyVidEqKey<'tcx>>,
 }
 
-pub struct TypeVariableTable<'a, 'tcx> {
+pub(crate) struct TypeVariableTable<'a, 'tcx> {
     storage: &'a mut TypeVariableStorage<'tcx>,
 
     undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
@@ -50,7 +50,7 @@ pub(crate) struct TypeVariableData {
 }
 
 #[derive(Copy, Clone, Debug)]
-pub enum TypeVariableValue<'tcx> {
+pub(crate) enum TypeVariableValue<'tcx> {
     Known { value: Ty<'tcx> },
     Unknown { universe: ty::UniverseIndex },
 }
@@ -58,14 +58,14 @@ pub enum TypeVariableValue<'tcx> {
 impl<'tcx> TypeVariableValue<'tcx> {
     /// If this value is known, returns the type it is known to be.
     /// Otherwise, `None`.
-    pub fn known(&self) -> Option<Ty<'tcx>> {
+    pub(crate) fn known(&self) -> Option<Ty<'tcx>> {
         match *self {
             TypeVariableValue::Unknown { .. } => None,
             TypeVariableValue::Known { value } => Some(value),
         }
     }
 
-    pub fn is_unknown(&self) -> bool {
+    pub(crate) fn is_unknown(&self) -> bool {
         match *self {
             TypeVariableValue::Unknown { .. } => true,
             TypeVariableValue::Known { .. } => false,
@@ -74,7 +74,7 @@ impl<'tcx> TypeVariableValue<'tcx> {
 }
 
 impl<'tcx> TypeVariableStorage<'tcx> {
-    pub fn new() -> TypeVariableStorage<'tcx> {
+    pub(crate) fn new() -> TypeVariableStorage<'tcx> {
         TypeVariableStorage {
             values: Default::default(),
             eq_relations: ut::UnificationTableStorage::new(),
@@ -105,14 +105,14 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     ///
     /// Note that this function does not return care whether
     /// `vid` has been unified with something else or not.
-    pub fn var_origin(&self, vid: ty::TyVid) -> TypeVariableOrigin {
+    pub(crate) fn var_origin(&self, vid: ty::TyVid) -> TypeVariableOrigin {
         self.storage.values[vid].origin
     }
 
     /// Records that `a == b`, depending on `dir`.
     ///
     /// Precondition: neither `a` nor `b` are known.
-    pub fn equate(&mut self, a: ty::TyVid, b: ty::TyVid) {
+    pub(crate) fn equate(&mut self, a: ty::TyVid, b: ty::TyVid) {
         debug_assert!(self.probe(a).is_unknown());
         debug_assert!(self.probe(b).is_unknown());
         self.eq_relations().union(a, b);
@@ -121,7 +121,7 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     /// Instantiates `vid` with the type `ty`.
     ///
     /// Precondition: `vid` must not have been previously instantiated.
-    pub fn instantiate(&mut self, vid: ty::TyVid, ty: Ty<'tcx>) {
+    pub(crate) fn instantiate(&mut self, vid: ty::TyVid, ty: Ty<'tcx>) {
         let vid = self.root_var(vid);
         debug_assert!(!ty.is_ty_var(), "instantiating ty var with var: {vid:?} {ty:?}");
         debug_assert!(self.probe(vid).is_unknown());
@@ -143,7 +143,7 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     /// - `origin`: indicates *why* the type variable was created.
     ///   The code in this module doesn't care, but it can be useful
     ///   for improving error messages.
-    pub fn new_var(
+    pub(crate) fn new_var(
         &mut self,
         universe: ty::UniverseIndex,
         origin: TypeVariableOrigin,
@@ -158,7 +158,7 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     }
 
     /// Returns the number of type variables created thus far.
-    pub fn num_vars(&self) -> usize {
+    pub(crate) fn num_vars(&self) -> usize {
         self.storage.values.len()
     }
 
@@ -167,42 +167,29 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
     /// will yield the same root variable (per the union-find
     /// algorithm), so `root_var(a) == root_var(b)` implies that `a ==
     /// b` (transitively).
-    pub fn root_var(&mut self, vid: ty::TyVid) -> ty::TyVid {
+    pub(crate) fn root_var(&mut self, vid: ty::TyVid) -> ty::TyVid {
         self.eq_relations().find(vid).vid
     }
 
     /// Retrieves the type to which `vid` has been instantiated, if
     /// any.
-    pub fn probe(&mut self, vid: ty::TyVid) -> TypeVariableValue<'tcx> {
+    pub(crate) fn probe(&mut self, vid: ty::TyVid) -> TypeVariableValue<'tcx> {
         self.inlined_probe(vid)
     }
 
     /// An always-inlined variant of `probe`, for very hot call sites.
     #[inline(always)]
-    pub fn inlined_probe(&mut self, vid: ty::TyVid) -> TypeVariableValue<'tcx> {
+    pub(crate) fn inlined_probe(&mut self, vid: ty::TyVid) -> TypeVariableValue<'tcx> {
         self.eq_relations().inlined_probe_value(vid)
     }
 
-    /// If `t` is a type-inference variable, and it has been
-    /// instantiated, then return the with which it was
-    /// instantiated. Otherwise, returns `t`.
-    pub fn replace_if_possible(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        match *t.kind() {
-            ty::Infer(ty::TyVar(v)) => match self.probe(v) {
-                TypeVariableValue::Unknown { .. } => t,
-                TypeVariableValue::Known { value } => value,
-            },
-            _ => t,
-        }
-    }
-
     #[inline]
     fn eq_relations(&mut self) -> super::UnificationTable<'_, 'tcx, TyVidEqKey<'tcx>> {
         self.storage.eq_relations.with_log(self.undo_log)
     }
 
     /// Returns a range of the type variables created during the snapshot.
-    pub fn vars_since_snapshot(
+    pub(crate) fn vars_since_snapshot(
         &mut self,
         value_count: usize,
     ) -> (Range<TyVid>, Vec<TypeVariableOrigin>) {
@@ -215,7 +202,7 @@ impl<'tcx> TypeVariableTable<'_, 'tcx> {
 
     /// Returns indices of all variables that are not yet
     /// instantiated.
-    pub fn unresolved_variables(&mut self) -> Vec<ty::TyVid> {
+    pub(crate) fn unresolved_variables(&mut self) -> Vec<ty::TyVid> {
         (0..self.num_vars())
             .filter_map(|i| {
                 let vid = ty::TyVid::from_usize(i);

compiler/rustc_infer/src/lib.rs

@@ -19,10 +19,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
-#![feature(box_patterns)]
 #![feature(extend_one)]
-#![feature(if_let_guard)]
-#![feature(iter_intersperse)]
 #![feature(iterator_try_collect)]
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]

compiler/rustc_middle/src/ty/relate.rs

@@ -212,15 +212,7 @@ impl<'tcx> Relate<TyCtxt<'tcx>> for ty::GenericArg<'tcx> {
             (ty::GenericArgKind::Const(a_ct), ty::GenericArgKind::Const(b_ct)) => {
                 Ok(relation.relate(a_ct, b_ct)?.into())
             }
-            (ty::GenericArgKind::Lifetime(unpacked), x) => {
+            _ => bug!("impossible case reached: can't relate: {a:?} with {b:?}"),
-                bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
-            }
-            (ty::GenericArgKind::Type(unpacked), x) => {
-                bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
-            }
-            (ty::GenericArgKind::Const(unpacked), x) => {
-                bug!("impossible case reached: can't relate: {:?} with {:?}", unpacked, x)
-            }
         }
     }
 }