… to `pattern_type_macro`

That's what the gates are actually gating, and the single char difference in naming was not helpful either

The `println!();` statement's span doesn't include the `;`, and the modified suggestions where trying to get the `;` by getting the differenece between the statement's and the expression's spans, which was an empty suggestion.

Fix rust-lang#133833, fix rust-lang#133834.

Centralize emitting an error in `const_to_pat` so that all errors from that evaluating a `const` in a pattern can add addditional information. With this, now point at the `const` item's definition:

```
error[E0158]: constant pattern depends on a generic parameter
  --> $DIR/associated-const-type-parameter-pattern.rs:20:9
   |
LL | pub trait Foo {
   | -------------
LL |     const X: EFoo;
   |     ------------- constant defined here
...
LL |         A::X => println!("A::X"),
   |         ^^^^
```

Silence errors that are implied by the errors in the `const` item definition.

Add a primary span label.

Conform to error style guide.

```
error[E0158]: constant pattern depends on a generic parameter, which is not allowed
  --> $DIR/associated-const-type-parameter-pattern.rs:20:9
   |
LL | pub trait Foo {
   | -------------
LL |     const X: EFoo;
   |     ------------- constant defined here
...
LL | pub fn test<A: Foo, B: Foo>(arg: EFoo) {
   |             - constant depends on this generic param
LL |     match arg {
LL |         A::X => println!("A::X"),
   |         ^^^^ `const` depends on a generic parameter
```

- Add primary span labels.
- Point at const generic parameter used as pattern.
- Point at statics used as pattern.
- Point at let bindings used in const pattern.

```
error: trait object `dyn Send` cannot be used in patterns
  --> $DIR/issue-70972-dyn-trait.rs:6:9
   |
LL | const F: &'static dyn Send = &7u32;
   | -------------------------- constant defined here
...
LL |         F => panic!(),
   |         ^ trait object can't be used in patterns
```

- Point at type that should derive `PartialEq` to be structural.
- Point at manual `impl PartialEq`, explaining that it is not sufficient to be structural.

```
error: constant of non-structural type `MyType` in a pattern
  --> $DIR/const-partial_eq-fallback-ice.rs:14:12
   |
LL | struct MyType;
   | ------------- `MyType` must be annotated with `#[derive(PartialEq)]` to be usable in patterns
...
LL | const CONSTANT: &&MyType = &&MyType;
   | ------------------------ constant defined here
...
LL |     if let CONSTANT = &&MyType {
   |            ^^^^^^^^ constant of non-structural type
   |
note: the `PartialEq` trait must be derived, manual `impl`s are not sufficient; see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
  --> $DIR/const-partial_eq-fallback-ice.rs:5:1
   |
LL | impl PartialEq<usize> for MyType {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

Unify wording with the regular non-structural type error.

…e" error

Point at types that need to be marked with `#[derive(PartialEq)]`.

We use a visitor to look at a type that isn't structural, looking for all ADTs that don't derive `PartialEq`. These can either be manual `impl PartialEq`s or no `impl` at all, so we differentiate between those two cases to provide more context to the user. We also only point at types and impls from the local crate, otherwise show only a note.

```
error: constant of non-structural type `&[B]` in a pattern
  --> $DIR/issue-61188-match-slice-forbidden-without-eq.rs:15:9
   |
LL | struct B(i32);
   | -------- must be annotated with `#[derive(PartialEq)]` to be usable in patterns
LL |
LL | const A: &[B] = &[];
   | ------------- constant defined here
...
LL |         A => (),
   |         ^ constant of non-structural type
   |
   = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
```

…isons, r=cjgillot

Add lint against function pointer comparisons

This is kind of a follow-up to rust-lang#117758 where we added a lint against wide pointer comparisons for being ambiguous and unreliable; well function pointer comparisons are also unreliable. We should IMO follow a similar logic and warn people about it.

-----

## `unpredictable_function_pointer_comparisons`

*warn-by-default*

The `unpredictable_function_pointer_comparisons` lint checks comparison of function pointer as the operands.

### Example

```rust
fn foo() {}
let a = foo as fn();

let _ = a == foo;
```

### Explanation

Function pointers comparisons do not produce meaningful result since they are never guaranteed to be unique and could vary between different code generation units. Furthermore different function could have the same address after being merged together.

----

This PR also uplift the very similar `clippy::fn_address_comparisons` lint, which only linted on if one of the operand was an `ty::FnDef` while this PR lints proposes to lint on all `ty::FnPtr` and `ty::FnDef`.

`@rustbot` labels +I-lang-nominated

~~Edit: Blocked on rust-lang/libs-team#323 being accepted and it's follow-up pr~~

…fmease

Fix suggestion when shorthand `self` has erroneous type

Fixes rust-lang#122086

r? estebank

Add context to "const in pattern" errors

*Each commit addresses specific diagnostics.*

- Add primary span labels
- Point at `const` item, and `const` generic param definition
- Reword messages and notes
- Point at generic param through which an associated `const` is being referenced
- Silence const in pattern with evaluation errors when they come from `const` items that already emit a diagnostic
- On non-structural type in const used as pattern, point at the type that should derive `PartialEq`

Do not emit empty suggestion

The `println!();` statement's span doesn't include the `;`, and the modified suggestions where trying to get the `;` by getting the differenece between the statement's and the expression's spans, which was an empty suggestion.

Fix rust-lang#133833, fix rust-lang#133834.

Rename `core_pattern_type` and `core_pattern_types` lib feature  gates to `pattern_type_macro`

That's what the gates are actually gating, and the single char difference in naming was not helpful either

fixes rust-lang#128987

…, r=oli-obk

No need to create placeholders for GAT args in confirm_object_candidate

We no longer need this logic to add placeholders for GAT args since with the removal of the `gat_extended` feature gate (rust-lang#133768) we no longer allow GATs in dyn trait anyways.

r? oli-obk

…li-obk

`fn_sig_for_fn_abi` should return a `ty::FnSig`, no need for a binder

r? oli-obk

Split out of rust-lang#133122