Rollup merge of #102336 - compiler-errors:issue-102333, r=jackh726

Fix associated type bindings with anon const in GAT position

The first commit formats `type_of.rs`, which is really hard to maintain since it uses a bunch of features like `let`-chains and `if let` match arm bindings. Best if you just review the second two diffs.

Fixes #102333

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -333,7 +333,12 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     find_opaque_ty_constraints_for_tait(tcx, def_id)
                 }
                 // Opaque types desugared from `impl Trait`.
-                ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner), in_trait, .. }) => {
+                ItemKind::OpaqueTy(OpaqueTy {
+                    origin:
+                        hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner),
+                    in_trait,
+                    ..
+                }) => {
                     if in_trait {
                         span_bug!(item.span, "impl-trait in trait has no default")
                     } else {
@@ -378,7 +383,9 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
 
         Node::Field(field) => icx.to_ty(field.ty),
 
-        Node::Expr(&Expr { kind: ExprKind::Closure{..}, .. }) => tcx.typeck(def_id).node_type(hir_id),
+        Node::Expr(&Expr { kind: ExprKind::Closure { .. }, .. }) => {
+            tcx.typeck(def_id).node_type(hir_id)
+        }
 
         Node::AnonConst(_) if let Some(param) = tcx.opt_const_param_of(def_id) => {
             // We defer to `type_of` of the corresponding parameter
@@ -410,30 +417,38 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                 | Node::Item(&Item { kind: ItemKind::GlobalAsm(asm), .. })
                     if asm.operands.iter().any(|(op, _op_sp)| match op {
                         hir::InlineAsmOperand::Const { anon_const }
-                        | hir::InlineAsmOperand::SymFn { anon_const } => anon_const.hir_id == hir_id,
+                        | hir::InlineAsmOperand::SymFn { anon_const } => {
+                            anon_const.hir_id == hir_id
+                        }
                         _ => false,
                     }) =>
                 {
                     tcx.typeck(def_id).node_type(hir_id)
                 }
 
-                Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => tcx
+                Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => {
-                    .adt_def(tcx.hir().get_parent_item(hir_id))
+                    tcx.adt_def(tcx.hir().get_parent_item(hir_id)).repr().discr_type().to_ty(tcx)
-                    .repr()
+                }
-                    .discr_type()
-                    .to_ty(tcx),
 
-                Node::TypeBinding(binding @ &TypeBinding { hir_id: binding_id, ..  })
+                Node::TypeBinding(
-                    if let Node::TraitRef(trait_ref) = tcx.hir().get(
+                    binding @ &TypeBinding {
-                        tcx.hir().get_parent_node(binding_id)
+                        hir_id: binding_id,
-                    ) =>
+                        kind: TypeBindingKind::Equality { term: Term::Const(ref e) },
+                        ..
+                    },
+                ) if let Node::TraitRef(trait_ref) =
+                    tcx.hir().get(tcx.hir().get_parent_node(binding_id))
+                    && e.hir_id == hir_id =>
                 {
                     let Some(trait_def_id) = trait_ref.trait_def_id() else {
                         return tcx.ty_error_with_message(DUMMY_SP, "Could not find trait");
                     };
                     let assoc_items = tcx.associated_items(trait_def_id);
                     let assoc_item = assoc_items.find_by_name_and_kind(
-                    tcx, binding.ident, ty::AssocKind::Const, def_id.to_def_id(),
+                        tcx,
+                        binding.ident,
+                        ty::AssocKind::Const,
+                        def_id.to_def_id(),
                     );
                     if let Some(assoc_item) = assoc_item {
                         tcx.type_of(assoc_item.def_id)
@@ -446,14 +461,56 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     }
                 }
 
+                Node::TypeBinding(
+                    binding @ &TypeBinding { hir_id: binding_id, gen_args, ref kind, .. },
+                ) if let Node::TraitRef(trait_ref) =
+                    tcx.hir().get(tcx.hir().get_parent_node(binding_id))
+                    && let Some((idx, _)) =
+                        gen_args.args.iter().enumerate().find(|(_, arg)| {
+                            if let GenericArg::Const(ct) = arg {
+                                ct.value.hir_id == hir_id
+                            } else {
+                                false
+                            }
+                        }) =>
+                {
+                    let Some(trait_def_id) = trait_ref.trait_def_id() else {
+                        return tcx.ty_error_with_message(DUMMY_SP, "Could not find trait");
+                    };
+                    let assoc_items = tcx.associated_items(trait_def_id);
+                    let assoc_item = assoc_items.find_by_name_and_kind(
+                        tcx,
+                        binding.ident,
+                        match kind {
+                            // I think `<A: T>` type bindings requires that `A` is a type
+                            TypeBindingKind::Constraint { .. }
+                            | TypeBindingKind::Equality { term: Term::Ty(..) } => {
+                                ty::AssocKind::Type
+                            }
+                            TypeBindingKind::Equality { term: Term::Const(..) } => {
+                                ty::AssocKind::Const
+                            }
+                        },
+                        def_id.to_def_id(),
+                    );
+                    if let Some(assoc_item) = assoc_item {
+                        tcx.type_of(tcx.generics_of(assoc_item.def_id).params[idx].def_id)
+                    } else {
+                        // FIXME(associated_const_equality): add a useful error message here.
+                        tcx.ty_error_with_message(
+                            DUMMY_SP,
+                            "Could not find associated const on trait",
+                        )
+                    }
+                }
+
                 Node::GenericParam(&GenericParam {
                     hir_id: param_hir_id,
                     kind: GenericParamKind::Const { default: Some(ct), .. },
                     ..
                 }) if ct.hir_id == hir_id => tcx.type_of(tcx.hir().local_def_id(param_hir_id)),
 
-                x =>
+                x => tcx.ty_error_with_message(
-                  tcx.ty_error_with_message(
                     DUMMY_SP,
                     &format!("unexpected const parent in type_of(): {x:?}"),
                 ),

src/test/ui/generic-associated-types/issue-102333.rs

@@ -0,0 +1,15 @@
+// check-pass
+
+trait A {
+    type T: B<U<1i32> = ()>;
+}
+
+trait B {
+    type U<const C: i32>;
+}
+
+fn f<T: A>() {
+    let _: <<T as A>::T as B>::U<1i32> = ();
+}
+
+fn main() {}