Ensure valid TraitRefs are created for GATs

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -914,6 +914,7 @@ impl<'a> State<'a> {
 
     pub fn print_assoc_constraint(&mut self, constraint: &ast::AssocTyConstraint) {
         self.print_ident(constraint.ident);
+        constraint.gen_args.as_ref().map(|args| self.print_generic_args(args, false));
         self.s.space();
         match &constraint.kind {
             ast::AssocTyConstraintKind::Equality { ty } => {

compiler/rustc_hir/src/lang_items.rs

@@ -238,6 +238,7 @@ language_item_table! {
 
     Deref,                   sym::deref,               deref_trait,                Target::Trait;
     DerefMut,                sym::deref_mut,           deref_mut_trait,            Target::Trait;
+    DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy;
     Receiver,                sym::receiver,            receiver_trait,             Target::Trait;
 
     Fn,                      kw::Fn,                   fn_trait,                   Target::Trait;

compiler/rustc_middle/src/ty/sty.rs

@@ -1112,22 +1112,6 @@ pub struct ProjectionTy<'tcx> {
 }
 
 impl<'tcx> ProjectionTy<'tcx> {
-    /// Construct a `ProjectionTy` by searching the trait from `trait_ref` for the
-    /// associated item named `item_name`.
-    pub fn from_ref_and_name(
-        tcx: TyCtxt<'_>,
-        trait_ref: ty::TraitRef<'tcx>,
-        item_name: Ident,
-    ) -> ProjectionTy<'tcx> {
-        let item_def_id = tcx
-            .associated_items(trait_ref.def_id)
-            .find_by_name_and_kind(tcx, item_name, ty::AssocKind::Type, trait_ref.def_id)
-            .unwrap()
-            .def_id;
-
-        ProjectionTy { substs: trait_ref.substs, item_def_id }
-    }
-
     /// Extracts the underlying trait reference from this projection.
     /// For example, if this is a projection of `<T as Iterator>::Item`,
     /// then this function would return a `T: Iterator` trait reference.

compiler/rustc_trait_selection/src/autoderef.rs

@@ -6,7 +6,6 @@ use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt, WithConstness};
 use rustc_middle::ty::{ToPredicate, TypeFoldable};
 use rustc_session::DiagnosticMessageId;
-use rustc_span::symbol::{sym, Ident};
 use rustc_span::Span;
 
 #[derive(Copy, Clone, Debug)]
@@ -146,11 +145,10 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         let normalized_ty = fulfillcx.normalize_projection_type(
             &self.infcx,
             self.param_env,
-            ty::ProjectionTy::from_ref_and_name(
-                tcx,
-                trait_ref,
-                Ident::with_dummy_span(sym::Target),
-            ),
+            ty::ProjectionTy {
+                item_def_id: tcx.lang_items().deref_target()?,
+                substs: trait_ref.substs,
+            },
             cause,
         );
         if let Err(e) = fulfillcx.select_where_possible(&self.infcx) {

library/core/src/ops/deref.rs

@@ -64,6 +64,7 @@ pub trait Deref {
     /// The resulting type after dereferencing.
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_diagnostic_item = "deref_target"]
+    #[cfg_attr(not(bootstrap), lang = "deref_target")]
     type Target: ?Sized;
 
     /// Dereferences the value.

src/test/pretty/gat-bounds.rs

@@ -13,4 +13,6 @@ impl X for () {
     type Y<T> where Self: Sized = u32;
 }
 
+fn f<T: X<Y<()> = i32>>() {}
+
 fn main() { }