Rollup merge of #105144 - compiler-errors:normalization-doc, r=lcnr

Document normalization methods `At::{normalize,query_normalize}`

r? ``@lcnr``

compiler/rustc_infer/src/infer/mod.rs

@@ -80,7 +80,6 @@ pub struct InferOk<'tcx, T> {
 }
 pub type InferResult<'tcx, T> = Result<InferOk<'tcx, T>, TypeError<'tcx>>;
 
-pub type Bound<T> = Option<T>;
 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"
 pub type FixupResult<'tcx, T> = Result<T, FixupError<'tcx>>; // "fixup result"
 

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -11,8 +11,8 @@ use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::util::impl_subject_and_oblig;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
-    self, Normalized, Obligation, ObligationCause, ObligationCtxt, PredicateObligation,
-    PredicateObligations, SelectionContext,
+    self, Obligation, ObligationCause, ObligationCtxt, PredicateObligation, PredicateObligations,
+    SelectionContext,
 };
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
@@ -30,6 +30,8 @@ use std::fmt::Debug;
 use std::iter;
 use std::ops::ControlFlow;
 
+use super::NormalizeExt;
+
 /// Whether we do the orphan check relative to this crate or
 /// to some remote crate.
 #[derive(Copy, Clone, Debug)]
@@ -128,8 +130,8 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
         predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
     };
 
-    let Normalized { value: mut header, obligations } =
-        traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
+    let InferOk { value: mut header, obligations } =
+        selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(header);
 
     header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
     header

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -56,7 +56,6 @@ pub use self::object_safety::astconv_object_safety_violations;
 pub use self::object_safety::is_vtable_safe_method;
 pub use self::object_safety::MethodViolationCode;
 pub use self::object_safety::ObjectSafetyViolation;
-pub(crate) use self::project::{normalize, normalize_to};
 pub use self::project::{normalize_projection_type, NormalizeExt};
 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};

compiler/rustc_trait_selection/src/traits/project.rs

@@ -50,6 +50,10 @@ pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::ProjectionTy<'tcx>>
 pub(super) struct InProgress;
 
 pub trait NormalizeExt<'tcx> {
+    /// Normalize a value using the `AssocTypeNormalizer`.
+    ///
+    /// This normalization should be used when the type contains inference variables or the
+    /// projection may be fallible.
     fn normalize<T: TypeFoldable<'tcx>>(&self, t: T) -> InferOk<'tcx, T>;
 }
 
@@ -57,7 +61,7 @@ impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
     fn normalize<T: TypeFoldable<'tcx>>(&self, value: T) -> InferOk<'tcx, T> {
         let mut selcx = SelectionContext::new(self.infcx);
         let Normalized { value, obligations } =
-            normalize(&mut selcx, self.param_env, self.cause.clone(), value);
+            normalize_with_depth(&mut selcx, self.param_env, self.cause.clone(), 0, value);
         InferOk { value, obligations }
     }
 }
@@ -303,37 +307,6 @@ fn project_and_unify_type<'cx, 'tcx>(
     }
 }
 
-/// Normalizes any associated type projections in `value`, replacing
-/// them with a fully resolved type where possible. The return value
-/// combines the normalized result and any additional obligations that
-/// were incurred as result.
-pub(crate) fn normalize<'a, 'b, 'tcx, T>(
-    selcx: &'a mut SelectionContext<'b, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    cause: ObligationCause<'tcx>,
-    value: T,
-) -> Normalized<'tcx, T>
-where
-    T: TypeFoldable<'tcx>,
-{
-    let mut obligations = Vec::new();
-    let value = normalize_to(selcx, param_env, cause, value, &mut obligations);
-    Normalized { value, obligations }
-}
-
-pub(crate) fn normalize_to<'a, 'b, 'tcx, T>(
-    selcx: &'a mut SelectionContext<'b, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    cause: ObligationCause<'tcx>,
-    value: T,
-    obligations: &mut Vec<PredicateObligation<'tcx>>,
-) -> T
-where
-    T: TypeFoldable<'tcx>,
-{
-    normalize_with_depth_to(selcx, param_env, cause, 0, value, obligations)
-}
-
 /// As `normalize`, but with a custom depth.
 pub(crate) fn normalize_with_depth<'a, 'b, 'tcx, T>(
     selcx: &'a mut SelectionContext<'b, 'tcx>,
@@ -2324,10 +2297,11 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         },
     ));
 
-    let ty = super::normalize_to(
+    let ty = normalize_with_depth_to(
         selcx,
         obligation.param_env,
         cause.clone(),
+        obligation.recursion_depth + 1,
         tcx.bound_trait_impl_trait_tys(impl_fn_def_id)
             .map_bound(|tys| {
                 tys.map_or_else(|_| tcx.ty_error(), |tys| tys[&obligation.predicate.item_def_id])

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

@@ -23,6 +23,13 @@ use super::NoSolution;
 pub use rustc_middle::traits::query::NormalizationResult;
 
 pub trait QueryNormalizeExt<'tcx> {
+    /// Normalize a value using the `QueryNormalizer`.
+    ///
+    /// This normalization should *only* be used when the projection does not
+    /// have possible ambiguity or may not be well-formed.
+    ///
+    /// After codegen, when lifetimes do not matter, it is preferable to instead
+    /// use [`TyCtxt::normalize_erasing_regions`], which wraps this procedure.
     fn query_normalize<T>(&self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
     where
         T: TypeFoldable<'tcx>;