When a delegation path like `reuse Trait::<> as bar4` has a child segment
that resolves to a trait instead of a function, the compiler would ICE
because `lower_generic_args_of_path` asserts that `self_ty` is `Some`
when `has_self` is true and `parent` is `None`.

Fix this by filtering out non-function child segments early using
`.filter()` in the method chain, so that when the child segment resolves
to a trait (error recovery for E0423), we skip generic args computation
entirely and return an empty list via `unwrap_or_default()`.

Also make `get_segment` return `Option` by using `opt_def_id()` instead
of `def_id()` to gracefully handle unresolved segments.

…range_end_end, r=davidtwco

Stop using rustc_layout_scalar_valid_range_* in rustc

*[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/152569)*

Another step towards rust-lang#135996

Required some manual impls, but we already do many manual impls for the newtype_index types, so it's not really a new maintenance burden.

…petrochenkov

Fix ICE in fn_delegation when child segment resolves to a trait

Fixes rust-lang#153420

When a delegation path like `reuse Trait::<> as bar4` has only one segment resolving to a trait (not a function), the child args processing in `get_delegation_user_specified_args` called `lower_generic_args_of_path` with `self_ty = None`. Since the trait's generics have `has_self = true`, this triggered
`assert!(self_ty.is_some())`.

Fix by computing and providing `self_ty` when the child segment's `def_id` has `has_self`. In valid delegation code the child segment always resolves to a function, so this only affects error recovery.

miri-test-libstd: use --tests and update some comments

rust-lang#153143 added `./x test --tests` matching `cargo --tests`, which is exactly what Miri wants when testing the standard library. So let's use it for that. We can then also remove a hack in `library/alloctests/benches/vec_deque_append.rs`.

Also update the comment for why the other benchmarks still need to be disabled in Miri, and remove some `cfg_attr` that seem unnecessary since the entire crate that contains them is already disabled in Miri. Those were copied over in rust-lang@b8fa843 -- they used to be needed since benches and tests were in the same crate, but they aren't any more.