Change:
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Assigning priority as discussed in the of the Prioritization Working Group. label -I-prioritize +P-low

Discussion:
use rustc_hir::intravisit::{walk_generics, Visitor as _}; use rustc_hir::lang_items::LangItem; use rustc_hir::{Constness, GenericArg, GenericArgs}; <del> use rustc_middle::ty::subst::{self, InternalSubsts, Subst, SubstsRef}; </del> <ins> use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef}; </ins> use rustc_middle::ty::GenericParamDefKind; use rustc_middle::ty::{self, Const, DefIdTree, Ty, TyCtxt, TypeFoldable}; use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;

tcx.ty_error().into() } else { // This is a default type parameter. <ins> let substs = substs.unwrap(); if substs.iter().any(|arg| match arg.unpack() { GenericArgKind::Type(ty) => ty.references_error(), _ => false, }) { // Avoid ICE #86756 when type error recovery goes awry. return tcx.ty_error().into(); } </ins> self.astconv .normalize_ty( self.span, tcx.at(self.span).type_of(param.def_id).subst_spanned( tcx, <del> substs.unwrap(), </del> <ins> substs, </ins> Some(self.span), ), )

<ins> trait Foo<T, T = T> {} //~^ ERROR the name `T` is already used for a generic parameter in this item's generic parameters fn eq<A, B>() { eq::<dyn, Foo> //~^ ERROR cannot find type `dyn` in this scope //~| ERROR missing generics for trait `Foo` //~| WARN trait objects without an explicit `dyn` are deprecated //~| WARN this is accepted in the current edition } fn main() {} </ins>

<ins> error[E0403]: the name `T` is already used for a generic parameter in this item's generic parameters --> $DIR/issue-86756.rs:1:14 | LL | trait Foo<T, T = T> {} |           -  ^ already used |           | |           first use of `T` error[E0412]: cannot find type `dyn` in this scope --> $DIR/issue-86756.rs:5:10 | LL | fn eq<A, B>() { |           - help: you might be missing a type parameter: `, dyn` LL |     eq::<dyn, Foo> |          ^^^ not found in this scope warning: trait objects without an explicit `dyn` are deprecated --> $DIR/issue-86756.rs:5:15 | LL |     eq::<dyn, Foo> |               ^^^ help: use `dyn`: `dyn Foo` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021! = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165> error[E0107]: missing generics for trait `Foo` --> $DIR/issue-86756.rs:5:15 | LL |     eq::<dyn, Foo> |               ^^^ expected at least 1 generic argument | note: trait defined here, with at least 1 generic parameter: `T` --> $DIR/issue-86756.rs:1:7 | LL | trait Foo<T, T = T> {} |       ^^^ - help: add missing generic argument | LL |     eq::<dyn, Foo<T>> |               ^^^^^^ error: aborting due to 3 previous errors; 1 warning emitted Some errors have detailed explanations: E0107, E0403, E0412. For more information about an error, try `rustc --explain E0107`. </ins>