…ath, r=JohnTitor

borrowck: Introduce BlameConstraint::to_obligation_cause_from_path()

Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`.

The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is.

For reference, `ObligationCause` was introdued by rust-lang#89249, but the codebase looked quite different back then.

This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in rust-lang#158623.

# Notes

I have removed the comment

```rs
        // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint.
        // Instead, we use it to produce an improved `ObligationCauseCode`.
````

because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient:

```rs
                // We handle predicates and opaque types specially; don't prioritize them here.
                ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4,
```

Rollup of 18 pull requests

Successful merges:

 - #158692 (Add release notes for 1.96.1)
 - #134021 (Implement `IntoIterator` for `[&[mut]] Box<[T; N], A>`)
 - #152860 (Port the `without_debuginfo` test from `backtrace-rs` to the testsuite)
 - #155932 (MIR Call terminator: evaluate destination place before arguments)
 - #156777 (Add -Zautodiff_post_passes flag to limit which llvm passes to run after enzyme to make autodiff tests more robust)
 - #157151 (JSON target specs: remove 'x86-softfloat' compatibility alias)
 - #157835 (expand free alias types in the auto-trait orphan check)
 - #158377 (add `-Zforce-intrinsic-fallback` flag)
 - #158434 (delegation: refactor AST -> HIR lowering)
 - #158552 (make some tidy errors around python easier to understand)
 - #158624 (borrowck: Introduce BlameConstraint::to_obligation_cause_from_path())
 - #158704 (Optimize `ArrayChunks::try_rfold` with `DoubleEndedIterator::next_chunk_back`)
 - #158711 (library: Comment on libtest's dicey internal soundness)
 - #158539 (Move `SizeHint` and `IoHandle` to `core::io`)
 - #158659 (refactor the normalization in `coerce_shared_info`)
 - #158689 (resolver: don't use `Finalize` when resolving visibilities during AST expansion)
 - #158698 (Update TypeVisitable implementation)
 - #158706 (Tweaks to MIR building scope API)

…ath, r=JohnTitor

borrowck: Introduce BlameConstraint::to_obligation_cause_from_path()

Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`.

The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is.

For reference, `ObligationCause` was introdued by rust-lang#89249, but the codebase looked quite different back then.

This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in rust-lang#158623.

# Notes

I have removed the comment

```rs
        // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint.
        // Instead, we use it to produce an improved `ObligationCauseCode`.
````

because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient:

```rs
                // We handle predicates and opaque types specially; don't prioritize them here.
                ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4,
```

…uwer

Rollup of 20 pull requests

Successful merges:

 - #158692 (Add release notes for 1.96.1)
 - #134021 (Implement `IntoIterator` for `[&[mut]] Box<[T; N], A>`)
 - #155932 (MIR Call terminator: evaluate destination place before arguments)
 - #155989 (Update `transmute_copy` to ub_checks and `?Sized`)
 - #156777 (Add -Zautodiff_post_passes flag to limit which llvm passes to run after enzyme to make autodiff tests more robust)
 - #157151 (JSON target specs: remove 'x86-softfloat' compatibility alias)
 - #157835 (expand free alias types in the auto-trait orphan check)
 - #157857 (Stabilize `#[my_macro] mod foo;` (part of `proc_macro_hygiene`))
 - #158377 (add `-Zforce-intrinsic-fallback` flag)
 - #158434 (delegation: refactor AST -> HIR lowering)
 - #158552 (make some tidy errors around python easier to understand)
 - #158624 (borrowck: Introduce BlameConstraint::to_obligation_cause_from_path())
 - #158704 (Optimize `ArrayChunks::try_rfold` with `DoubleEndedIterator::next_chunk_back`)
 - #158711 (library: Comment on libtest's dicey internal soundness)
 - #158751 (rustdoc: Fix crash when trying to inline foreign item which cannot have attributes)
 - #158539 (Move `SizeHint` and `IoHandle` to `core::io`)
 - #158659 (refactor the normalization in `coerce_shared_info`)
 - #158689 (resolver: don't use `Finalize` when resolving visibilities during AST expansion)
 - #158698 (Update TypeVisitable implementation)
 - #158706 (Tweaks to MIR building scope API)

…uwer

Rollup of 19 pull requests

Successful merges:

 - #158692 (Add release notes for 1.96.1)
 - #134021 (Implement `IntoIterator` for `[&[mut]] Box<[T; N], A>`)
 - #155932 (MIR Call terminator: evaluate destination place before arguments)
 - #155989 (Update `transmute_copy` to ub_checks and `?Sized`)
 - #156777 (Add -Zautodiff_post_passes flag to limit which llvm passes to run after enzyme to make autodiff tests more robust)
 - #157151 (JSON target specs: remove 'x86-softfloat' compatibility alias)
 - #157835 (expand free alias types in the auto-trait orphan check)
 - #157857 (Stabilize `#[my_macro] mod foo;` (part of `proc_macro_hygiene`))
 - #158434 (delegation: refactor AST -> HIR lowering)
 - #158552 (make some tidy errors around python easier to understand)
 - #158624 (borrowck: Introduce BlameConstraint::to_obligation_cause_from_path())
 - #158704 (Optimize `ArrayChunks::try_rfold` with `DoubleEndedIterator::next_chunk_back`)
 - #158711 (library: Comment on libtest's dicey internal soundness)
 - #158751 (rustdoc: Fix crash when trying to inline foreign item which cannot have attributes)
 - #158539 (Move `SizeHint` and `IoHandle` to `core::io`)
 - #158659 (refactor the normalization in `coerce_shared_info`)
 - #158689 (resolver: don't use `Finalize` when resolving visibilities during AST expansion)
 - #158698 (Update TypeVisitable implementation)
 - #158706 (Tweaks to MIR building scope API)

Rollup merge of #158624 - Enselic:to_obligation_cause_from_path, r=JohnTitor

borrowck: Introduce BlameConstraint::to_obligation_cause_from_path()

Before this commit, `BlameConstraint` is a bit hard to understand at first, because of its `ObligationCause` field. In practice, `BlameConstraint` is just a slimmed down version of an `OutlivesConstraint` from `Vec<OutlivesConstraint>`.

The artificial `ObligationCause` is only needed in one place. Rather than having that exception polute the lower level logic, bubble it up as much as we can. That way, it becomes clearer what `BlameConstraint` actually is.

For reference, `ObligationCause` was introdued by #89249, but the codebase looked quite different back then.

This takes us one step closer (this is commit 1 of 4) towards the end result illustrated in #158623.

# Notes

I have removed the comment

```rs
        // We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint.
        // Instead, we use it to produce an improved `ObligationCauseCode`.
````

because I think [this](https://github.com/rust-lang/rust/blob/e2af9c03ef4cfb769e391968a5cfbb1afe6f01e2/compiler/rustc_borrowck/src/region_infer/mod.rs#L1763-L1762) existing comment is sufficient:

```rs
                // We handle predicates and opaque types specially; don't prioritize them here.
                ConstraintCategory::Predicate(_) | ConstraintCategory::OpaqueType => 4,
```