There are several indications that we should not ZST as a ScalarInt:
- We had two ways to have ZST valtrees, either an empty `Branch` or a `Leaf` with a ZST in it.
  `ValTree::zst()` used the former, but the latter could possibly arise as well.
- Likewise, the interpreter had `Immediate::Uninit` and `Immediate::Scalar(Scalar::ZST)`.
- LLVM codegen already had to special-case ZST ScalarInt.

So instead add new ZST variants to those types that did not have other variants
which could be used for this purpose.

Rollup of 7 pull requests

Successful merges:

 - #98350 (Implement support for DWARF version 5.)
 - #98915 (Clarify deriving code)
 - #98980 (fix ICE in ConstProp)
 - #99008 (Adding suggestion for E0530)
 - #99043 (Collapse some weirdly-wrapping derives)
 - #99048 (Remove a string comparison about types)
 - #99070 (Update integer_atomics tracking issue)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Update integer_atomics tracking issue

Updates #32976.
Updates #99069.

r? ``@RalfJung``

Remove a string comparison about types

Collapse some weirdly-wrapping derives

self-explanatory

Adding suggestion for E0530

Closes #98974

fix ICE in ConstProp

Fixes https://github.com/rust-lang/rust/issues/96169

Clarify deriving code

A number of clarifications to the deriving code.

r? ``@Mark-Simulacrum``

Implement support for DWARF version 5.

DWARF version 5 brings a number of improvements over version 4. Quoting from
the announcement [1]:

> Version 5 incorporates improvements in many areas: better data compression,
> separation of debugging data from executable files, improved description of
> macros and source files, faster searching for symbols, improved debugging
> optimized code, as well as numerous improvements in functionality and
> performance.

On platforms where DWARF version 5 is supported (Linux, primarily), this commit
adds support for it behind a new `-Z dwarf-version=5` flag.

[1]: https://dwarfstd.org/Public_Review.php

r? ``@michaelwoerister``

Miscellaneous inlining improvements

Add `#[inline]` to a few trivial non-generic methods from a perf report
that otherwise wouldn't be candidates for inlining.

Only enable ConstProp on opt level >= 1

r? `@JakobDegen`

Track implicit `Sized` obligations in type params

When we evaluate `ty::GenericPredicates` we introduce the implicit
`Sized` predicate of type params, but we do so with only the `Predicate`
its `Span` as context, we don't have an `Obligation` or
`ObligationCauseCode` we could influence. To try and carry this
information through, we add a new field to `ty::GenericPredicates` that
tracks both which predicates come from a type param and whether that
param has any bounds already (to use in suggestions).

We also suggest adding a `?Sized` bound if appropriate on E0599.

Address part of #98539.

`cs_fold` has four distinct cases, covered by three different function
arguments:

- first field
- combine current field with previous results
- no fields
- non-matching enum variants

This commit clarifies things by replacing the three function arguments
with one that takes a new `CsFold` type with four slightly different)
cases

- single field
- combine result for current field with results for previous fields
- no fields
- non-matching enum variants

This makes the code shorter and clearer.

This makes `cs_cmp`, `cs_partial_cmp`, and `cs_op` (for `PartialEq`)
more similar. It also fixes some out of date comments.

When deriving functions for zero-variant enums, we just generated a
function body that calls `std::instrincs::unreachable`. There is a large
comment with some not-very-useful historical discussion about
alternatives, including some discussion of feature-gating zero-variant
enums, which is clearly irrelevant today.

This commit cuts the comment down greatly.

The deriving code has some complex parts involving iterations over
selflike args and also fields within structs and enum variants.

The return types for a few functions demonstrate this:

- `TraitDef::create_{struct_pattern,enum_variant_pattern}` returns a
  `(P<ast::Pat>, Vec<(Span, Option<Ident>, P<Expr>)>)`
- `TraitDef::create_struct_field_accesses` returns a `Vec<(Span,
  Option<Ident>, P<Expr>)>`.

This results in per-field data stored within per-selflike-arg data, with
lots of repetition within the per-field data elements. This then has to
be "transposed" in two places (`expand_struct_method_body` and
`expand_enum_method_body`) into per-self-like-arg data stored within
per-field data. It's all quite clumsy and confusing.

This commit rearranges things greatly. Data is obtained in the needed
form up-front, avoiding the need for transposition. Also, various
functions are split, removed, and added, to make things clearer and
avoid tuple return values.

The diff is hard to read, which reflects the messiness of the original
code -- there wasn't an easy way to break these changes into small
pieces. (Sorry!) It's a net reduction of 35 lines and a readability
improvement. The generated code is unchanged.

It's unused. This also removes the need for the lifetime on `FieldInfo`,
which is nice.

Use `self_exprs` and `other_selflike_exprs` in a manner similar to the
previous commit.

The deriving code has inconsistent terminology to describe args.

In some places it distinguishes between:
- the `&self` arg (if present), versus
- all other args.

In other places it distinguishes between:
- the `&self` arg (if present) and any other arguments with the same
  type (in practice there is at most one, e.g. in `PartialEq::eq`),
  versus
- all other args.

The terms "self_args" and "nonself_args" are sometimes used for the
former distinction, and sometimes for the latter. "args" is also
sometimes used for "all other args".

This commit makes the code consistently uses "self_args"/"nonself_args"
for the former and "selflike_args"/"nonselflike_args" for the latter.
This change makes the code easier to read.

The commit also adds a panic on an impossible path (the `Self_` case) in
`extract_arg_details`.

Updates #32976.
Updates #99069.

update Miri

Fixes https://github.com/rust-lang/rust/issues/98922
r? `@ghost`

DWARF version 5 brings a number of improvements over version 4. Quoting from
the announcement [1]:

> Version 5 incorporates improvements in many areas: better data compression,
> separation of debugging data from executable files, improved description of
> macros and source files, faster searching for symbols, improved debugging
> optimized code, as well as numerous improvements in functionality and
> performance.

On platforms where DWARF version 5 is supported (Linux, primarily), this commit
adds support for it behind a new `-Z dwarf-version=5` flag.

[1]: https://dwarfstd.org/Public_Review.php

don't succeed `evaluate_obligation` query if new opaque types were registered

fixes #98608
fixes #98604

The root cause of all this is that in type flag computation we entirely ignore nongeneric things like struct fields and the signature of function items. So if a flag had to be set for a struct if it is set for a field, that will only happen if the field is generic, as only the generic parameters are checked.

I now believe we cannot use type flags to handle opaque types. They seem like the wrong tool for this.

Instead, this PR replaces the previous logic by adding a new variant of `EvaluatedToOk`: `EvaluatedToOkModuloOpaqueTypes`, which says that there were some opaque types that got hidden types bound, but that binding may not have been legal (because we don't know if the opaque type was in its defining scope or not).

Rollup of 4 pull requests

Successful merges:

 - #98533 (Add a `-Zdump-drop-tracking-cfg` debugging flag)
 - #98654 (An optimization for `pest-2.1.3`)
 - #98657 (Migrate some diagnostics from `rustc_const_eval` to `SessionDiagnostic`)
 - #98794 (Highlight conflicting param-env candidates)

Failed merges:

 - #98957 ( don't allow ZST in ScalarInt )

r? `@ghost`
`@rustbot` modify labels: rollup

Highlight conflicting param-env candidates

This could probably be further improved by noting _why_ equivalent param-env candidates (modulo regions) leads to ambiguity.

Fixes #98786

Migrate some diagnostics from `rustc_const_eval` to `SessionDiagnostic`

I'm still trying to get the hang of this, so it doesn't migrate _all_ of `rustc_const_eval`. Working on that later.

r? `@davidtwco`

An optimization for `pest-2.1.3`

An easy win I found while looking at a profile of `pest-2.1.3`. It's also a small code cleanup.

r? `@pnkfelix`

Add a `-Zdump-drop-tracking-cfg` debugging flag

This is useful for debugging drop-tracking; previously, you had to recompile
rustc from source and manually add a call to `write_graph_to_file`. This
makes the option more discoverable and configurable at runtime.

I also took the liberty of making the labels for the CFG nodes much easier to read:
previously, they looked like `id(2), local_id: 48`, now they look like
```
expr from_config (hir_id=HirId { owner: DefId(0:10 ~ default_struct_update[79f9]::foo), local_id: 2})
```

r? ``@eholk``

More derive output improvements

This PR includes:
- Some test improvements.
- Some cosmetic changes to derive output that make the code look more like what a human would write.
- Some more fundamental improvements to `cmp` and `partial_cmp` generation.

r? `@Mark-Simulacrum`

Use less string interning

This removes string interning in a couple of places where doing so won't result in perf improvements. I also switched one place to use pre-interned symbols.

Rollup of 6 pull requests

Successful merges:

 - #95635 (sess: stabilize `--terminal-width` as `--diagnostic-width`)
 - #98718 (Stabilize `into_future`)
 - #98795 (A few cleanups)
 - #98798 (Fix caching bug in `download-rustc = true`)
 - #99019 (Add doc comments in `rustc_middle::mir`)
 - #99026 (Add test for and fix rust-lang/rust-clippy#9131)

Failed merges:

 - #98957 ( don't allow ZST in ScalarInt )

r? `@ghost`
`@rustbot` modify labels: rollup

Add test for and fix rust-lang/rust-clippy#9131

This lint seems to have been broken by #98446 -- but of course, there was no clippy test for this case at the time.

`expr.span.ctxt().outer_expn_data()` now has `MacroKind::Derive` instead of `MacroKind::Attr` for something like:

```
#[derive(Clone, Debug)]
pub struct UnderscoreInStruct {
    _foo: u32,
}
```

---

changelog: none

closes: https://github.com/rust-lang/rust-clippy/issues/9131

Add doc comments in `rustc_middle::mir`