Rollup merge of #122687 - lcnr:normalizes-to-emit-nested-goals, r=compiler-errors

`NormalizesTo`: return nested goals to caller

Fixes the regression of `paperclip-core`. see https://hackmd.io/IsVAafiOTAaPIFcUxRJufw for more details.

r? ```@compiler-errors```

compiler/rustc_middle/src/traits/solve.rs

@@ -164,6 +164,19 @@ pub struct ExternalConstraintsData<'tcx> {
     // FIXME: implement this.
     pub region_constraints: QueryRegionConstraints<'tcx>,
     pub opaque_types: Vec<(ty::OpaqueTypeKey<'tcx>, Ty<'tcx>)>,
+    pub normalization_nested_goals: NestedNormalizationGoals<'tcx>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default, TypeVisitable, TypeFoldable)]
+pub struct NestedNormalizationGoals<'tcx>(pub Vec<(GoalSource, Goal<'tcx, ty::Predicate<'tcx>>)>);
+impl<'tcx> NestedNormalizationGoals<'tcx> {
+    pub fn empty() -> Self {
+        NestedNormalizationGoals(vec![])
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
 }
 
 // FIXME: Having to clone `region_constraints` for folding feels bad and
@@ -183,6 +196,10 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
                 .iter()
                 .map(|opaque| opaque.try_fold_with(folder))
                 .collect::<Result<_, F::Error>>()?,
+            normalization_nested_goals: self
+                .normalization_nested_goals
+                .clone()
+                .try_fold_with(folder)?,
         }))
     }
 
@@ -190,6 +207,7 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
         TypeFolder::interner(folder).mk_external_constraints(ExternalConstraintsData {
             region_constraints: self.region_constraints.clone().fold_with(folder),
             opaque_types: self.opaque_types.iter().map(|opaque| opaque.fold_with(folder)).collect(),
+            normalization_nested_goals: self.normalization_nested_goals.clone().fold_with(folder),
         })
     }
 }
@@ -197,7 +215,8 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
     fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, visitor: &mut V) -> V::Result {
         try_visit!(self.region_constraints.visit_with(visitor));
-        self.opaque_types.visit_with(visitor)
+        try_visit!(self.opaque_types.visit_with(visitor));
+        self.normalization_nested_goals.visit_with(visitor)
     }
 }
 
@@ -239,7 +258,7 @@ impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for PredefinedOpaques<'tcx> {
 ///
 /// This is necessary as we treat nested goals different depending on
 /// their source.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, TypeVisitable, TypeFoldable)]
 pub enum GoalSource {
     Misc,
     /// We're proving a where-bound of an impl.
@@ -256,12 +275,6 @@ pub enum GoalSource {
     ImplWhereBound,
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, HashStable)]
-pub enum IsNormalizesToHack {
-    Yes,
-    No,
-}
-
 /// Possible ways the given goal can be proven.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CandidateSource {

compiler/rustc_middle/src/traits/solve/inspect.rs

@@ -19,8 +19,8 @@
 //! [canonicalized]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
 
 use super::{
-    CandidateSource, Canonical, CanonicalInput, Certainty, Goal, GoalSource, IsNormalizesToHack,
-    NoSolution, QueryInput, QueryResult,
+    CandidateSource, Canonical, CanonicalInput, Certainty, Goal, GoalSource, NoSolution,
+    QueryInput, QueryResult,
 };
 use crate::{infer::canonical::CanonicalVarValues, ty};
 use format::ProofTreeFormatter;
@@ -50,7 +50,7 @@ pub type CanonicalState<'tcx, T> = Canonical<'tcx, State<'tcx, T>>;
 #[derive(Eq, PartialEq)]
 pub enum GoalEvaluationKind<'tcx> {
     Root { orig_values: Vec<ty::GenericArg<'tcx>> },
-    Nested { is_normalizes_to_hack: IsNormalizesToHack },
+    Nested,
 }
 
 #[derive(Eq, PartialEq)]

compiler/rustc_middle/src/traits/solve/inspect/format.rs

@@ -55,10 +55,7 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
     pub(super) fn format_goal_evaluation(&mut self, eval: &GoalEvaluation<'_>) -> std::fmt::Result {
         let goal_text = match eval.kind {
             GoalEvaluationKind::Root { orig_values: _ } => "ROOT GOAL",
-            GoalEvaluationKind::Nested { is_normalizes_to_hack } => match is_normalizes_to_hack {
-                IsNormalizesToHack::No => "GOAL",
-                IsNormalizesToHack::Yes => "NORMALIZES-TO HACK GOAL",
-            },
+            GoalEvaluationKind::Nested => "GOAL",
         };
         write!(self.f, "{}: {:?}", goal_text, eval.uncanonicalized_goal)?;
         self.nested(|this| this.format_canonical_goal_evaluation(&eval.evaluation))