Remove hir::ArrayLen

[voidc]

This refactoring removes hir::ArrayLen, replacing it with hir::ConstArg. To represent inferred array lengths (previously hir::ArrayLen::Infer), a new variant ConstArgKind::Infer is added.

r? @BoxyUwU

[voidc]

- | 1: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[d56d]::function_with_bytes), UserArgs { args: [UnevaluatedConst { def: DefId(0:8 ~ issue_99325[d56d]::main::{constant#1}), args: [] }], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:14:16: 14:68, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}
+ | 1: user_ty: Canonical { value: TypeOf(DefId(0:3 ~ issue_99325[d56d]::function_with_bytes), UserArgs { args: [&*b"AAAA"], user_self_ty: None }), max_universe: U0, variables: [] }, span: $DIR/issue_99325.rs:14:16: 14:68, inferred_ty: fn() -> &'static [u8] {function_with_bytes::<&*b"AAAA">}

I think this is because I now normalize all ConstArgs in lower_const_arg. The diff doesn't look wrong to me, can I just bless it?

[BoxyUwU]

Very cool :3 thanks for doing this

[BoxyUwU]

This change would be why we dont want to normalize at the end of lower_const_arg. User type annotations exist to remember the "unnormalized as written by the user" types/generic arguments in MIR so that any lifetime constraints introduced by them can be known to the borrow checker instead of being ignored :3

This specific example isn't wrong per se but in the general case it would be with const arguments that use lifetime parameters, e.g.:

#![feature(min_generic_const_args)]

trait Trait<'a> {
  const ASSOC: usize;
}

impl Trait<'static> for u8 {
  const ASSOC: usize = 10;
}

struct Bar<const N: usize>;

fn foo<'a>() {
  let _: Bar<<u8 as Trait<'a>>::ASSOC>;
}

<u8 as Trait<'a>>::ASSOC being well formed requires 'a: 'static which doesn't hold so we should error in borrow checking. This is accomplished by having a user type annotation of <u8 as Trait<'a>>::ASSOC so that borrow checking knows 'a: 'static must hold. With this change we'd have a user type annotation of 10 which doesn't tell borrow checking anything about 'a: 'static having to hold :3

Though this example won't actually do anything right now since min_generic_const_args hasn't been implemented :3

[rustbot]

HIR ty lowering was modified

cc @fmease

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[BoxyUwU]

can you squash these commits then r=me

[aDotInTheVoid]

@bors r=boxyuwu

[bors]

📌 Commit d38f013 has been approved by boxyuwu

It is now in the queue for this repository.