Support middle::ty assoc const eq predicates again

6 files changed, 92 insertions, 119 deletions

diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 0ddb0466c29..7658e7ad35f 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -371,10 +371,9 @@ fn clean_where_predicate<'tcx>(
             bounds: wrp.bounds.iter().filter_map(|x| clean_generic_bound(x, cx)).collect(),
         },
 
-        hir::WherePredicateKind::EqPredicate(wrp) => WherePredicate::EqPredicate {
-            lhs: clean_ty(wrp.lhs_ty, cx),
-            rhs: clean_ty(wrp.rhs_ty, cx).into(),
-        },
+        // We should never actually reach this case because these predicates should've already been
+        // rejected in an earlier compiler pass. This feature isn't fully implemented (#20041).
+        hir::WherePredicateKind::EqPredicate(_) => bug!("EqPredicate"),
     })
 }
 
@@ -470,46 +469,34 @@ fn clean_projection_predicate<'tcx>(
     cx: &mut DocContext<'tcx>,
 ) -> WherePredicate {
     WherePredicate::EqPredicate {
-        lhs: clean_projection(
-            pred.map_bound(|p| {
-                // FIXME: This needs to be made resilient for `AliasTerm`s that
-                // are associated consts.
-                p.projection_term.expect_ty(cx.tcx)
-            }),
-            cx,
-            None,
-        ),
+        lhs: clean_projection(pred.map_bound(|p| p.projection_term), cx, None),
         rhs: clean_middle_term(pred.map_bound(|p| p.term), cx),
     }
 }
 
 fn clean_projection<'tcx>(
-    ty: ty::Binder<'tcx, ty::AliasTy<'tcx>>,
+    proj: ty::Binder<'tcx, ty::AliasTerm<'tcx>>,
     cx: &mut DocContext<'tcx>,
-    def_id: Option<DefId>,
-) -> Type {
-    if cx.tcx.is_impl_trait_in_trait(ty.skip_binder().def_id) {
-        return clean_middle_opaque_bounds(cx, ty.skip_binder().def_id, ty.skip_binder().args);
-    }
-
+    parent_def_id: Option<DefId>,
+) -> QPathData {
     let trait_ = clean_trait_ref_with_constraints(
         cx,
-        ty.map_bound(|ty| ty.trait_ref(cx.tcx)),
+        proj.map_bound(|proj| proj.trait_ref(cx.tcx)),
         ThinVec::new(),
     );
-    let self_type = clean_middle_ty(ty.map_bound(|ty| ty.self_ty()), cx, None, None);
-    let self_def_id = if let Some(def_id) = def_id {
-        cx.tcx.opt_parent(def_id).or(Some(def_id))
-    } else {
-        self_type.def_id(&cx.cache)
+    let self_type = clean_middle_ty(proj.map_bound(|proj| proj.self_ty()), cx, None, None);
+    let self_def_id = match parent_def_id {
+        Some(parent_def_id) => cx.tcx.opt_parent(parent_def_id).or(Some(parent_def_id)),
+        None => self_type.def_id(&cx.cache),
     };
     let should_fully_qualify = should_fully_qualify_path(self_def_id, &trait_, &self_type);
-    Type::QPath(Box::new(QPathData {
-        assoc: projection_to_path_segment(ty, cx),
-        should_fully_qualify,
+
+    QPathData {
+        assoc: projection_to_path_segment(proj, cx),
         self_type,
+        should_fully_qualify,
         trait_: Some(trait_),
-    }))
+    }
 }
 
 fn should_fully_qualify_path(self_def_id: Option<DefId>, trait_: &Path, self_type: &Type) -> bool {
@@ -520,18 +507,17 @@ fn should_fully_qualify_path(self_def_id: Option<DefId>, trait_: &Path, self_typ
 }
 
 fn projection_to_path_segment<'tcx>(
-    ty: ty::Binder<'tcx, ty::AliasTy<'tcx>>,
+    proj: ty::Binder<'tcx, ty::AliasTerm<'tcx>>,
     cx: &mut DocContext<'tcx>,
 ) -> PathSegment {
-    let def_id = ty.skip_binder().def_id;
-    let item = cx.tcx.associated_item(def_id);
+    let def_id = proj.skip_binder().def_id;
     let generics = cx.tcx.generics_of(def_id);
     PathSegment {
-        name: item.name(),
+        name: cx.tcx.item_name(def_id),
         args: GenericArgs::AngleBracketed {
             args: clean_middle_generic_args(
                 cx,
-                ty.map_bound(|ty| &ty.args[generics.parent_count..]),
+                proj.map_bound(|ty| &ty.args[generics.parent_count..]),
                 false,
                 def_id,
             ),
@@ -845,7 +831,7 @@ fn clean_ty_generics<'tcx>(
         .predicates
         .iter()
         .flat_map(|(pred, _)| {
-            let mut projection = None;
+            let mut proj_pred = None;
             let param_idx = {
                 let bound_p = pred.kind();
                 match bound_p.skip_binder() {
@@ -860,7 +846,7 @@ fn clean_ty_generics<'tcx>(
                     ty::ClauseKind::Projection(p)
                         if let ty::Param(param) = p.projection_term.self_ty().kind() =>
                     {
-                        projection = Some(bound_p.rebind(p));
+                        proj_pred = Some(bound_p.rebind(p));
                         Some(param.index)
                     }
                     _ => None,
@@ -874,22 +860,12 @@ fn clean_ty_generics<'tcx>(
 
                 bounds.extend(pred.get_bounds().into_iter().flatten().cloned());
 
-                if let Some(proj) = projection
-                    && let lhs = clean_projection(
-                        proj.map_bound(|p| {
-                            // FIXME: This needs to be made resilient for `AliasTerm`s that
-                            // are associated consts.
-                            p.projection_term.expect_ty(cx.tcx)
-                        }),
-                        cx,
-                        None,
-                    )
-                    && let Some((_, trait_did, name)) = lhs.projection()
-                {
+                if let Some(pred) = proj_pred {
+                    let lhs = clean_projection(pred.map_bound(|p| p.projection_term), cx, None);
                     impl_trait_proj.entry(param_idx).or_default().push((
-                        trait_did,
-                        name,
-                        proj.map_bound(|p| p.term),
+                        lhs.trait_.unwrap().def_id(),
+                        lhs.assoc,
+                        pred.map_bound(|p| p.term),
                     ));
                 }
 
@@ -2146,14 +2122,8 @@ pub(crate) fn clean_middle_ty<'tcx>(
                 .map(|pb| AssocItemConstraint {
                     assoc: projection_to_path_segment(
                         pb.map_bound(|pb| {
-                            pb
-                                // HACK(compiler-errors): Doesn't actually matter what self
-                                // type we put here, because we're only using the GAT's args.
-                                .with_self_ty(cx.tcx, cx.tcx.types.self_param)
+                            pb.with_self_ty(cx.tcx, cx.tcx.types.trait_object_dummy_self)
                                 .projection_term
-                                // FIXME: This needs to be made resilient for `AliasTerm`s
-                                // that are associated consts.
-                                .expect_ty(cx.tcx)
                         }),
                         cx,
                     ),
@@ -2186,18 +2156,25 @@ pub(crate) fn clean_middle_ty<'tcx>(
             Tuple(t.iter().map(|t| clean_middle_ty(bound_ty.rebind(t), cx, None, None)).collect())
         }
 
-        ty::Alias(ty::Projection, data) => {
-            clean_projection(bound_ty.rebind(data), cx, parent_def_id)
+        ty::Alias(ty::Projection, alias_ty @ ty::AliasTy { def_id, args, .. }) => {
+            if cx.tcx.is_impl_trait_in_trait(def_id) {
+                clean_middle_opaque_bounds(cx, def_id, args)
+            } else {
+                Type::QPath(Box::new(clean_projection(
+                    bound_ty.rebind(alias_ty.into()),
+                    cx,
+                    parent_def_id,
+                )))
+            }
         }
 
-        ty::Alias(ty::Inherent, alias_ty) => {
-            let def_id = alias_ty.def_id;
+        ty::Alias(ty::Inherent, alias_ty @ ty::AliasTy { def_id, .. }) => {
             let alias_ty = bound_ty.rebind(alias_ty);
             let self_type = clean_middle_ty(alias_ty.map_bound(|ty| ty.self_ty()), cx, None, None);
 
             Type::QPath(Box::new(QPathData {
                 assoc: PathSegment {
-                    name: cx.tcx.associated_item(def_id).name(),
+                    name: cx.tcx.item_name(def_id),
                     args: GenericArgs::AngleBracketed {
                         args: clean_middle_generic_args(
                             cx,
@@ -2214,20 +2191,15 @@ pub(crate) fn clean_middle_ty<'tcx>(
             }))
         }
 
-        ty::Alias(ty::Free, data) => {
+        ty::Alias(ty::Free, ty::AliasTy { def_id, args, .. }) => {
             if cx.tcx.features().lazy_type_alias() {
                 // Free type alias `data` represents the `type X` in `type X = Y`. If we need `Y`,
                 // we need to use `type_of`.
-                let path = clean_middle_path(
-                    cx,
-                    data.def_id,
-                    false,
-                    ThinVec::new(),
-                    bound_ty.rebind(data.args),
-                );
+                let path =
+                    clean_middle_path(cx, def_id, false, ThinVec::new(), bound_ty.rebind(args));
                 Type::Path { path }
             } else {
-                let ty = cx.tcx.type_of(data.def_id).instantiate(cx.tcx, data.args);
+                let ty = cx.tcx.type_of(def_id).instantiate(cx.tcx, args);
                 clean_middle_ty(bound_ty.rebind(ty), cx, None, None)
             }
         }
@@ -2314,18 +2286,17 @@ fn clean_middle_opaque_bounds<'tcx>(
             let bindings: ThinVec<_> = bounds
                 .iter()
                 .filter_map(|(bound, _)| {
-                    if let ty::ClauseKind::Projection(proj) = bound.kind().skip_binder()
-                        && proj.projection_term.trait_ref(cx.tcx) == trait_ref.skip_binder()
+                    let bound = bound.kind();
+                    if let ty::ClauseKind::Projection(proj_pred) = bound.skip_binder()
+                        && proj_pred.projection_term.trait_ref(cx.tcx) == trait_ref.skip_binder()
                     {
                         return Some(AssocItemConstraint {
                             assoc: projection_to_path_segment(
-                                // FIXME: This needs to be made resilient for `AliasTerm`s that
-                                // are associated consts.
-                                bound.kind().rebind(proj.projection_term.expect_ty(cx.tcx)),
+                                bound.rebind(proj_pred.projection_term),
                                 cx,
                             ),
                             kind: AssocItemConstraintKind::Equality {
-                                term: clean_middle_term(bound.kind().rebind(proj.term), cx),
+                                term: clean_middle_term(bound.rebind(proj_pred.term), cx),
                             },
                         });
                     }
diff --git a/src/librustdoc/clean/simplify.rs b/src/librustdoc/clean/simplify.rs
index 41943b94d1e..40efa997868 100644
--- a/src/librustdoc/clean/simplify.rs
+++ b/src/librustdoc/clean/simplify.rs
@@ -46,11 +46,8 @@ pub(crate) fn where_clauses(cx: &DocContext<'_>, clauses: ThinVec<WP>) -> ThinVe
     // Look for equality predicates on associated types that can be merged into
     // general bound predicates.
     equalities.retain(|(lhs, rhs)| {
-        let Some((ty, trait_did, name)) = lhs.projection() else {
-            return true;
-        };
-        let Some((bounds, _)) = tybounds.get_mut(ty) else { return true };
-        merge_bounds(cx, bounds, trait_did, name, rhs)
+        let Some((bounds, _)) = tybounds.get_mut(&lhs.self_type) else { return true };
+        merge_bounds(cx, bounds, lhs.trait_.as_ref().unwrap().def_id(), lhs.assoc.clone(), rhs)
     });
 
     // And finally, let's reassemble everything
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 8a6bcdff6f3..7ba75d4a8c9 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -1341,7 +1341,7 @@ impl PreciseCapturingArg {
 pub(crate) enum WherePredicate {
     BoundPredicate { ty: Type, bounds: Vec<GenericBound>, bound_params: Vec<GenericParamDef> },
     RegionPredicate { lifetime: Lifetime, bounds: Vec<GenericBound> },
-    EqPredicate { lhs: Type, rhs: Term },
+    EqPredicate { lhs: QPathData, rhs: Term },
 }
 
 impl WherePredicate {
@@ -1704,14 +1704,6 @@ impl Type {
         matches!(self, Type::Tuple(v) if v.is_empty())
     }
 
-    pub(crate) fn projection(&self) -> Option<(&Type, DefId, PathSegment)> {
-        if let QPath(box QPathData { self_type, trait_, assoc, .. }) = self {
-            Some((self_type, trait_.as_ref()?.def_id(), assoc.clone()))
-        } else {
-            None
-        }
-    }
-
     /// Use this method to get the [DefId] of a [clean] AST node, including [PrimitiveType]s.
     ///
     /// [clean]: crate::clean
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 31e3cb73fa2..6ab1520386d 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -1019,12 +1019,27 @@ fn fmt_type(
             f.write_str("impl ")?;
             print_generic_bounds(bounds, cx).fmt(f)
         }
-        &clean::QPath(box clean::QPathData {
-            ref assoc,
-            ref self_type,
-            ref trait_,
-            should_fully_qualify,
-        }) => {
+        clean::QPath(qpath) => qpath.print(cx).fmt(f),
+    }
+}
+
+impl clean::Type {
+    pub(crate) fn print(&self, cx: &Context<'_>) -> impl Display {
+        fmt::from_fn(move |f| fmt_type(self, f, false, cx))
+    }
+}
+
+impl clean::Path {
+    pub(crate) fn print(&self, cx: &Context<'_>) -> impl Display {
+        fmt::from_fn(move |f| resolved_path(f, self.def_id(), self, false, false, cx))
+    }
+}
+
+impl clean::QPathData {
+    fn print(&self, cx: &Context<'_>) -> impl Display {
+        let Self { ref assoc, ref self_type, should_fully_qualify, ref trait_ } = *self;
+
+        fmt::from_fn(move |f| {
             // FIXME(inherent_associated_types): Once we support non-ADT self-types (#106719),
             // we need to surround them with angle brackets in some cases (e.g. `<dyn …>::P`).
 
@@ -1090,19 +1105,7 @@ fn fmt_type(
             }?;
 
             assoc.args.print(cx).fmt(f)
-        }
-    }
-}
-
-impl clean::Type {
-    pub(crate) fn print(&self, cx: &Context<'_>) -> impl Display {
-        fmt::from_fn(move |f| fmt_type(self, f, false, cx))
-    }
-}
-
-impl clean::Path {
-    pub(crate) fn print(&self, cx: &Context<'_>) -> impl Display {
-        fmt::from_fn(move |f| resolved_path(f, self.def_id(), self, false, false, cx))
+        })
     }
 }
 
diff --git a/src/librustdoc/json/conversions.rs b/src/librustdoc/json/conversions.rs
index bfcb794b89a..3ade40940bc 100644
--- a/src/librustdoc/json/conversions.rs
+++ b/src/librustdoc/json/conversions.rs
@@ -468,6 +468,9 @@ impl FromClean<clean::WherePredicate> for WherePredicate {
                     .collect(),
             },
             EqPredicate { lhs, rhs } => WherePredicate::EqPredicate {
+                // The LHS currently has type `Type` but it should be a `QualifiedPath` since it may
+                // refer to an associated const. However, `EqPredicate` shouldn't exist in the first
+                // place: <https://github.com/rust-lang/rust/141368>.
                 lhs: lhs.into_json(renderer),
                 rhs: rhs.into_json(renderer),
             },
@@ -557,12 +560,7 @@ impl FromClean<clean::Type> for Type {
                 is_mutable: mutability == ast::Mutability::Mut,
                 type_: Box::new((*type_).into_json(renderer)),
             },
-            QPath(box clean::QPathData { assoc, self_type, trait_, .. }) => Type::QualifiedPath {
-                name: assoc.name.to_string(),
-                args: Box::new(assoc.args.into_json(renderer)),
-                self_type: Box::new(self_type.into_json(renderer)),
-                trait_: trait_.map(|trait_| trait_.into_json(renderer)),
-            },
+            QPath(qpath) => (*qpath).into_json(renderer),
             // FIXME(unsafe_binder): Implement rustdoc-json.
             UnsafeBinder(_) => todo!(),
         }
@@ -579,6 +577,19 @@ impl FromClean<clean::Path> for Path {
     }
 }
 
+impl FromClean<clean::QPathData> for Type {
+    fn from_clean(qpath: clean::QPathData, renderer: &JsonRenderer<'_>) -> Self {
+        let clean::QPathData { assoc, self_type, should_fully_qualify: _, trait_ } = qpath;
+
+        Self::QualifiedPath {
+            name: assoc.name.to_string(),
+            args: Box::new(assoc.args.into_json(renderer)),
+            self_type: Box::new(self_type.into_json(renderer)),
+            trait_: trait_.map(|trait_| trait_.into_json(renderer)),
+        }
+    }
+}
+
 impl FromClean<clean::Term> for Term {
     fn from_clean(term: clean::Term, renderer: &JsonRenderer<'_>) -> Term {
         match term {
diff --git a/tests/rustdoc/inline_cross/assoc-const-equality.rs b/tests/rustdoc/inline_cross/assoc-const-equality.rs
index ec5c2f748ef..36ab027ef71 100644
--- a/tests/rustdoc/inline_cross/assoc-const-equality.rs
+++ b/tests/rustdoc/inline_cross/assoc-const-equality.rs
@@ -1,6 +1,5 @@
 //@ aux-crate:assoc_const_equality=assoc-const-equality.rs
 //@ edition:2021
-//@ ignore-test (FIXME: #125092)
 
 #![crate_name = "user"]