Prevent promotion of const fn calls in inline consts
We don't wanna make that mistake we did for statics and consts worse by letting more code use it.
r? ``@RalfJung``
cc https://github.com/rust-lang/rust/issues/76001
Improve invalid UTF-8 lint by finding the expression initializer
This PR introduce a small mechanism to walk up the HIR through bindings, if/else, consts, ... when trying lint on invalid UTF-8.
Fixes https://github.com/rust-lang/rust/issues/115208
rustc_target/loongarch: Fix passing of transparent unions with only one non-ZST member
This ensures that `MaybeUninit<T>` has the same ABI as `T` when passed through an `extern "C"` function.
Fixes https://github.com/rust-lang/rust/issues/115509
r? `@bjorn3`
Correctly deny late-bound lifetimes from parent in anon consts and TAITs
Reuse the `AnonConstBoundary` scope (introduced in #108553, renamed in this PR to `LateBoundary`) to deny late-bound vars of *all* kinds (ty/const/lifetime) in anon consts and TAITs.
Side-note, but I would like to consolidate this with the error reporting for RPITs (E0657):
c4f25777a0/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs (L733-L754) but the semantics about what we're allowed to capture there are slightly different, so I'm leaving that untouched.
Fixes#115474
Detect cycle errors hidden by opaques during monomorphization
Opaque types may reveal to projections, which themselves normalize to opaques. We don't currently normalize when checking that opaques are cyclical, and we may also not know that the opaque is cyclical until monomorphization (see `tests/ui/type-alias-impl-trait/mututally-recursive-overflow.rs`).
Detect cycle errors in `normalize_projection_ty` and report a fatal overflow (in the old solver). Luckily, this is already detected as a fatal overflow in the new solver.
Fixes#112047
rustc_target/riscv: Fix passing of transparent unions with only one non-ZST member
This ensures that `MaybeUninit<T>` has the same ABI as `T` when passed through an `extern "C"` function.
Fixes https://github.com/rust-lang/rust/issues/115481.
r? `@RalfJung`
This function is now used to check `#[panic_handler]`, `start` lang item, `main`, `#[start]` and intrinsic functions.
The diagnosis produced are now closer to the ones produced by trait/impl method signature mismatch.
Don't complain on a single non-exhaustive 1-ZST
r? RalfJung, though you mentioned being busy, so feel free to reassign.
This doesn't actually attempt to make the diagnostic better, so when we have two non-exhaustive 1-ZSTs in a struct, we still just point to one. 🤷Fixes#115922
Explain HRTB + infer limitations of old solver
Add a helpful message when we hit the limitation of the old trait solver where we don't properly normalize GATs with infer vars + bound vars, leading to too-eagerly reporting trait errors that would be later satisfied due to inference.
Make `TyKind::Adt`'s `Debug` impl be more pretty
Currently `{:?}` on `Ty` for a `TyKind::Adt` would print as `Adt(Foo, [])`. This PR changes it to be `Foo` when there are no generics or `Foo<T>`/`Foo<T, U>` when there _are_ generics. Example from debug log:
`├─0ms DEBUG rustc_hir_analysis::astconv return=Bar<T/#0, U/#1>`
I should have done this in my initial PR for a prettier TyKind: Debug impl but I thought I would need to be accessing generics_of to figure out where in the "path" the generics would have to go??? but no, adts literally only have a single place the generics can go (on the end). Feel a bit silly about this :)
r? `@oli-obk`
Avoid blessing cargo deps's source code in ui tests
Before this PR, the source code of dependencies was included in UI test error messages whenever possible. Unfortunately, "whenever possible" means in some cases the source code wouldn't be injected, resulting in a test failure.
One such case is when `$CARGO_HOME` is remapped to something that is not present on disk [^1]. As the remapped path doesn't exist on disk, the source code wouldn't be showed in `tests/ui/issues/issue-21763.rs`:
```diff
= note: required for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>` to implement `Send`
note: required because it appears within the type `HashMap<Rc<()>, Rc<()>, RandomState>`
--> $HASHBROWN_SRC_LOCATION
- |
-LL | pub struct HashMap<K, V, S = DefaultHashBuilder, A: Allocator + Clone = Global> {
- | ^^^^^^^
note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
--> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
note: required by a bound in `foo`
```
This PR fixes the problem by always hiding dependencies source code in the error messages generated during UI tests. This is implemented with a new internal flag, `-Z ignore-directory-in-diagnostics-source-blocks=$path`, which compiletest passes during UI tests. Once this is merged, remapping the Cargo home will be supported.
This PR is best reviewed commit-by-commit.
[^1]: After being puzzled for a bit, I discovered why this never impacted `rust-lang/rust`: we don't remap `$CARGO_HOME` 😅. Instead, we set `$CARGO_HOME` to `/cargo` in CI, which sort-of-but-not-really achieves the same effect.
move required_consts check to general post-mono-check function
This factors some code that is common between the interpreter and the codegen backends into shared helper functions. Also as a side-effect the interpreter now uses the same `eval` functions as everyone else to get the evaluated MIR constants.
Also this is in preparation for another post-mono check that will be needed for (the current hackfix for) https://github.com/rust-lang/rust/issues/115709: ensuring that all locals are dynamically sized.
I didn't expect this to change diagnostics, but it's just cycle errors that change.
r? `@oli-obk`
repr(transparent): it's fine if the one non-1-ZST field is a ZST
This code currently gets rejected:
```rust
#[repr(transparent)]
struct MyType([u16; 0])
```
That clearly seems like a bug to me: `repr(transparent)` [got defined ](https://github.com/rust-lang/rust/issues/77841#issuecomment-716575747) as having any number of 1-ZST fields plus optionally one more field; `MyType` clearly satisfies that definition.
This PR changes the `repr(transparent)` logic to actually match that definition.
Rollup of 6 pull requests
Successful merges:
- #114965 (Remove Drop impl of mpsc Receiver and (Sync)Sender)
- #115434 (make `Debug` impl for `ascii::Char` match that of `char`)
- #115477 (Stabilize the `Saturating` type)
- #115611 (add diagnostic for raw identifiers in format string)
- #115654 (improve PassMode docs)
- #115862 (Migrate `compiler/rustc_hir_typeck/src/callee.rs` to translatable diagnostics)
r? `@ghost`
`@rustbot` modify labels: rollup
add diagnostic for raw identifiers in format string
Format strings don't support raw identifiers (e.g. `format!("{r#type}")`), but they do support keywords in the format string directly (e.g. `format!("{type}")`). This PR improves the error output when attempting to use a raw identifier in a format string and adds a machine-applicable suggestion to remove the `r#`.
fixes https://github.com/rust-lang/rust/issues/115466
`#[diagnostic::on_unimplemented]` without filters
This commit adds support for a `#[diagnostic::on_unimplemented]` attribute with the following options:
* `message` to customize the primary error message
* `note` to add a customized note message to an error message
* `label` to customize the label part of the error message
The relevant behavior is specified in [RFC-3366](https://rust-lang.github.io/rfcs/3366-diagnostic-attribute-namespace.html)
impl Step for IP addresses
ACP: rust-lang/libs-team#235
Note: since this is insta-stable, it requires an FCP.
Separating out from the bit operations PR since it feels logically disjoint, and so their FCPs can be separate.
closure field capturing: don't depend on alignment of packed fields
This fixes the closure field capture part of https://github.com/rust-lang/rust/issues/115305: field capturing always stops at projections into packed structs, no matter the alignment of the field. This means changing a private field type from `u8` to `u64` can never change how closures capture fields, which is probably what we want.
Here's an example where, before this PR, changing the type of a private field in a repr(Rust) struct can change the output of a program:
```rust
#![allow(dead_code)]
mod m {
// before patch
#[derive(Default)]
pub struct S1(u8);
// after patch
#[derive(Default)]
pub struct S2(u64);
}
struct NoisyDrop;
impl Drop for NoisyDrop {
fn drop(&mut self) {
eprintln!("dropped!");
}
}
#[repr(packed)]
struct MyType {
field: m::S1, // output changes when this becomes S2
other_field: NoisyDrop,
third_field: Vec<()>,
}
fn test(r: MyType) {
let c = || {
let _val = std::ptr::addr_of!(r.field);
let _val = r.third_field;
};
drop(c);
eprintln!("before dropping");
}
fn main() {
test(MyType {
field: Default::default(),
other_field: NoisyDrop,
third_field: Vec::new(),
});
}
```
Of course this is a breaking change for the same reason that doing field capturing in the first place was a breaking change. Packed fields are relatively rare and depending on drop order is relatively rare, so I don't expect this to have much impact, but it's hard to be sure and even a crater run will only tell us so much.
Also see the [nomination comment](https://github.com/rust-lang/rust/pull/115315#issuecomment-1702807825).
Cc `@rust-lang/wg-rfc-2229` `@ehuss`
Make useless_ptr_null_checks smarter about some std functions
This teaches the `useless_ptr_null_checks` lint that some std functions can't ever return null pointers, because they need to point to valid data, get references as input, etc.
This is achieved by introducing an `#[rustc_never_returns_null_ptr]` attribute and adding it to these std functions (gated behind bootstrap `cfg_attr`).
Later on, the attribute could maybe be used to tell LLVM that the returned pointer is never null. I don't expect much impact of that though, as the functions are pretty shallow and usually the input data is already never null.
Follow-up of PR #113657Fixes#114442
Fallback effects even if types also fallback
`||` is short circuiting, so if we do ty/int var fallback, we *don't* do effect fallback 😸
r? `@fee1-dead` or `@oli-obk`
Fixes#115791Fixes#115842
Improve invalid let expression handling
- Move all of the checks for valid let expression positions to parsing.
- Add a field to ExprKind::Let in AST/HIR to mark whether it's in a valid location.
- Suppress some later errors and MIR construction for invalid let expressions.
- Fix a (drop) scope issue that was also responsible for #104172.
Fixes#104172Fixes#104868
Paper over an accidental regression
r? types
cc https://github.com/rust-lang/rust/issues/115781 (do not close issue until beta backport has been performed)
The PR reasons are explained with comments in the source.
In order to keep the diff simple, this PR effectively reverts https://github.com/rust-lang/rust/pull/113661, but only for RPITs. I will submit a follow up PR that fixes this correctly instead of just disabling the newly added check for RPITs. This PR should be significantly easier to review for beta backport
Properly consider binder vars in `HasTypeFlagsVisitor`
Given a PolyTraitRef like `for<'a> Ty: Trait` (where neither `Ty` nor `Trait` mention `'a`), we do *not* return true for `.has_type_flags(TypeFlags::HAS_LATE_BOUND)`, even though binders are supposed to act as if they have late-bound vars even if they don't mention them in their bound value: 31ae3b2bdb. This is because we use `HasTypeFlagsVisitor`, which only computes the type flags for `Ty`, `Const` and `Region` and `Predicates`, and we consequently skip any binders (and setting flags for their vars) that are not contained in one of these types.
This ends up causing a problem, because when we call `TyCtxt::erase_regions` (which both erases regions *and* anonymizes bound vars), we will skip such a PolyTraitRef, not anonymizing it, and therefore not making it structurally equal to other binders. This breaks vtable computations.
This PR computes the flags for all binders we enter in `HasTypeFlagsVisitor` if we're looking for `TypeFlags::HAS_LATE_BOUND` (or `TypeFlags::HAS_{RE,TY,CT}_LATE_BOUND`).
Fixes#115807
Fix the error message for `#![feature(no_coverage)]`
When #114656 was written, the feature flag to replace `no_coverage` was originally spelled `coverage`, but it was eventually changed to `coverage_attribute` instead.
That update happened to miss this error message in `removed.rs`, and unfortunately I only noticed just *after* the original PR was approved and merged.
cc ``@bossmc`` (original author) ``@oli-obk`` (original reviewer)
``@rustbot`` label +A-code-coverage
some ConstValue refactoring
In particular, use AllocId instead of Allocation in ConstValue::ByRef. This helps avoid redundant AllocIds when a `ByRef` constant gets put back into the interpreter.
r? `@oli-obk`
Fixes https://github.com/rust-lang/rust/issues/105536
Rework `no_coverage` to `coverage(off)`
As discussed at the tail of https://github.com/rust-lang/rust/issues/84605 this replaces the `no_coverage` attribute with a `coverage` attribute that takes sub-parameters (currently `off` and `on`) to control the coverage instrumentation.
Allows future-proofing for things like `coverage(off, reason="Tested live", issue="#12345")` or similar.
cleanup leftovers of const_err lint
Some code / comments seem to not have been updated when const_err was turned into a hard error, so we can do a bit of cleanup here.
r? `@oli-obk`
- Add doc comment to new type
- Restore "only supported directly in conditions of `if` and `while` expressions" note
- Rename variant with clearer name
This commit adds support for a `#[diagnostic::on_unimplemented]`
attribute with the following options:
* `message` to customize the primary error message
* `note` to add a customized note message to an error message
* `label` to customize the label part of the error message
Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>
Co-authored-by: Michael Goulet <michael@errs.io>
test ABI compatibility for some unsized types as well
and test for what `DispatchFromDyn` needs.
Also I ran this on a whole bunch of targets via Miri and added enough `cfg` to make it all work, as documentation for what does and doesn't currently work. (Most of those targets do not have their tests run on CI anyway.)
Here's the shell rune I used for that:
```
for TARGET in x86_64-unknown-linux-gnu x86_64-pc-windows-gnu aarch64-unknown-linux-gnu s390x-unknown-linux-gnu mips64-unknown-linux-gnuabi64 sparc64-unknown-linux-gnu powerpc64-unknown-linux-gnu powerpc64le-unknown-linux-gnu riscv64gc-unknown-linux-gnu loongarch64-unknown-linux-gnu wasm32-unknown-unknown; do
BOOTSTRAP_SKIP_TARGET_SANITY=1 ./x.py run miri --stage 0 --args tests/ui/abi/compatibility.rs --target $TARGET;
done
```
Rollup of 8 pull requests
Successful merges:
- #115548 (Extract parallel operations in `rustc_data_structures::sync` into a new `parallel` submodule)
- #115591 (Add regression test for LLVM 17-rc3 miscompile)
- #115631 (Don't ICE when computing ctype's `repr_nullable_ptr` for possibly-unsized ty)
- #115708 (fix homogeneous_aggregate not ignoring some ZST)
- #115730 (Some more small driver refactors)
- #115749 (Allow loading the SMIR for constants and statics)
- #115757 (Add a test for #108030)
- #115761 (Update books)
r? `@ghost`
`@rustbot` modify labels: rollup
fix homogeneous_aggregate not ignoring some ZST
This is an ABI-breaking change, because it fixes bugs in our ABI code. I'm not sure what that means for this PR, we don't really have a process for such changes, do we? I can only hope nobody relied on the old buggy behavior.
Fixes https://github.com/rust-lang/rust/issues/115664
Don't ICE when computing ctype's `repr_nullable_ptr` for possibly-unsized ty
We may not always be able to compute the layout of a type like `&T` when `T: ?Sized`, even if we're able to estimate its size skeleton.
r? davidtwco
Fixes#115628
Bubble up opaque <eq> opaque operations instead of picking an order
In case we are in `Bubble` mode (meaning every opaque type that is defined in the current crate is treated as if it were in its defining scope), we don't try to register an opaque type as the hidden type of another opaque type, but instead bubble up an obligation to equate them at the query caller site. Usually that means we have a `DefiningAnchor::Bind` and thus can reliably figure out whether an opaque type is in its defining scope. Where we can't, we'll error out, so the default is sound.
With this change we start using `AliasTyEq` predicates in the old solver, too.
fixes https://github.com/rust-lang/rust/issues/108498
But also regresses `tests/ui/impl-trait/anon_scope_creep.rs`. Our use of `Bubble` for `check_opaque_type_well_formed` is going to keep biting us.
r? `@lcnr` `@compiler-errors`
Previously some invalid let expressions would result in both a feature
error and a parsing error. Avoid this and ensure that we only emit the
parsing error when this happens.
There was an incomplete version of the check in parsing and a second
version in AST validation. This meant that some, but not all, invalid
uses were allowed inside macros/disabled cfgs. It also means that later
passes have a hard time knowing when the let expression is in a valid
location, sometimes causing ICEs.
- Add a field to ExprKind::Let in AST/HIR to mark whether it's in a
valid location.
- Suppress later errors and MIR construction for invalid let
expressions.
Improve diagnostic for generic params from outer items (E0401)
Generalize the wording of E0401 to talk about *outer items* instead of *outer functions* since the current phrasing is outdated. The outer item can be a function, constant, trait, ADT or impl block (see the new UI test for the more exotic examples).
Further, don't suggest introducing generic parameters to constant items unless the feature `generic_const_items` is enabled.
Lastly, make E0401 translatable while we're at it.
Fixes#115720.
Fix incorrect mutable suggestion information for binding in ref pattern like: `let &b = a;`
fixes#114896
I find we have to get pat_span but not local_decl.source_info.span for suggestion. In `let &b = a;` pat_span is &b. I think check `let &b = a` in hir to make sure it is hir::Node::Local(hir::Local {pat: hir::Pat{kind: hir::PatKind::Ref(....... can distinguish it from other situation, but I'm not sure.
If my processing method is not accurate, please guide me to modify it, thank you.
r? `@davidtwco`
The `Debug` impl for `Ty` just calls the `Display` impl for `Ty`. This
is surprising and annoying. In particular, it means `Debug` doesn't show
as much information as `Debug` for `TyKind` does. And `Debug` is used in
some user-facing error messages, which seems bad.
This commit changes the `Debug` impl for `Ty` to call the `Debug` impl
for `TyKind`. It also does a number of follow-up changes to preserve
existing output, many of which involve inserting
`with_no_trimmed_paths!` calls. It also adds `Display` impls for
`UserType` and `Canonical`.
Some tests have changes to expected output:
- Those that use the `rustc_abi(debug)` attribute.
- Those that use the `EMIT_MIR` annotation.
In each case the output is slightly uglier than before. This isn't
ideal, but it's pretty weird (particularly for the attribute) that the
output is using `Debug` in the first place. They're fairly obscure
attributes (I hadn't heard of them) so I'm not worried by this.
For `async-is-unwindsafe.stderr`, there is one line that now lacks a
full path. This is a consistency improvement, because all the other
mentions of `Context` in this test lack a path.
The lint panicked for an input like 'extern "C" fn(Option<&<T as FooTrait>::FooType>)' because the type T therein cannot be normalized. The normalization failure caused SizeSkeleton::compute() to return an error and trigger a panic in the unwrap().
Fix sanitize/cfg.rs test
* Move needs-sanitizer conditions to specific revisions that require them (otherwise the conditions are mutually exclusive with needs-sanitizer-kcfi and test is always ignored).
* Add missing revisions
Improve "associated type not found" diagnostics
```rs
use core::ops::Deref;
fn foo<T>() where T: Deref<Output = u32> {}
```
Before:
```
error[E0220]: associated type `Output` not found for `Deref`
--> E0220.rs:5:28
|
5 | fn foo<T>() where T: Deref<Output = u32> {}
| ^^^^^^ associated type `Output` not found
```
After:
```
error[E0220]: associated type `Output` not found for `Deref`
--> E0220.rs:5:28
|
5 | fn foo<T>() where T: Deref<Output = u32> {}
| ^^^^^^ help: `Deref` has the following associated type: `Target`
```
---
`@rustbot` label +A-diagnostics +D-papercut
Rollup of 6 pull requests
Successful merges:
- #104299 (Clarify stability guarantee for lifetimes in enum discriminants)
- #115088 (Fix Step Skipping Caused by Using the `--exclude` Option)
- #115201 (rustdoc: list matching impls on type aliases)
- #115633 (Lint node for `PRIVATE_BOUNDS`/`PRIVATE_INTERFACES` is the item which names the private type)
- #115638 (`-Cllvm-args` usability improvement)
- #115643 (fix: return early when has tainted in mir-lint)
r? `@ghost`
`@rustbot` modify labels: rollup
* Move needs-sanitizer conditions to specific revisions that
require them (otherwise the conditions are mutually exclusive
with needs-sanitizer-kcfi and test is always ignored).
* Add missing revisions
fix: return early when has tainted in mir-lint
Fixes#115203
`a[..]` is of indeterminate size, it had been reported error during borrow check, therefore we skip the mir lint process.
Lint node for `PRIVATE_BOUNDS`/`PRIVATE_INTERFACES` is the item which names the private type
The HIR that the `PRIVATE_BOUNDS` lint should be attached to is the item that has the *bounds*, not the private type. This PR also aligns this behavior with the `EXPORTED_PRIVATE_DEPENDENCIES` lint, which also requires putting the `allow` on the item that names the private type.
Fixes#115475
r? petrochenkov
diagnostics: add test case for trait bounds diagnostic
Closes#82038
It was fixed by https://github.com/rust-lang/rust/pull/89580, a wide-reaching obligation tracking improvement. This commit adds a test case.
Don't suggest dereferencing to unsized type
Rudimentary check that the self type is Sized. I don't really like any of this diagnostics code -- it's really messy and also really prone to false positives and negatives, but oh well.
Fixes#115569
Print the path of a return-position impl trait in trait when `return_type_notation` is enabled
When we're printing a return-position impl trait in trait, we usually just print it like an opaque. This is *usually* fine, but can be confusing when using `return_type_notation`. Print the path of the method from where the RPITIT originates when this feature gate is enabled.
Don't require `Drop` for `[PhantomData<T>; N]` where `N` and `T` are generic, if `T` requires `Drop`
fixes https://github.com/rust-lang/rust/issues/115403
fixes https://github.com/rust-lang/rust/issues/115410
This was accidentally regressed in https://github.com/rust-lang/rust/pull/114134, because it was accidentally stabilized in #102204 (cc `@rust-lang/lang,` seems like an innocent stabilization, considering this PR is more of a bugfix than a feature).
While we have a whole month to beta backport this change before the regression hits stable, I'd still prefer not to go through an FCP on this PR (which fixes a regression), if T-lang wants an FCP, I can can open an issue about the change itself.
Stabilize `PATH` option for `--print KIND=PATH`
This PR propose stabilizing the `PATH` option for `--print KIND=PATH`. This option was previously added in https://github.com/rust-lang/rust/pull/113780 (as insta-stable before being un-stablized in https://github.com/rust-lang/rust/pull/114139).
Description of the `PATH` option:
> A filepath may optionally be specified for each requested information kind, in the format `--print KIND=PATH`, just like for `--emit`. When a path is specified, information will be written there instead of to stdout.
------
Description of the original PR [\[link\]](https://github.com/rust-lang/rust/pull/113780#issue-1807080607):
> **Support --print KIND=PATH command line syntax**
>
> As is already done for `--emit KIND=PATH` and `-L KIND=PATH`.
>
> In the discussion of https://github.com/rust-lang/rust/pull/110785, it was pointed out that `--print KIND=PATH` is nicer than trying to apply the single global `-o path` to `--print`'s output, because in general there can be multiple print requests within a single rustc invocation, and anyway `-o` would already be used for a different meaning in the case of `link-args` and `native-static-libs`.
>
> I am interested in using `--print cfg=PATH` in Buck2. Currently Buck2 works around the lack of support for `--print KIND=PATH` by [indirecting through a Python wrapper script](d43cf3a51a/prelude/rust/tools/get_rustc_cfg.py) to redirect rustc's stdout into the location dictated by the build system.
>
> From skimming Cargo's usages of `--print`, it definitely seems like it would benefit from `--print KIND=PATH` too. Currently it is working around the lack of this by inserting `--crate-name=___ --print=crate-name` so that it can look for a line containing `___` as a delimiter between the 2 other `--print` informations it actually cares about. This is commented as a "HACK" and "abuse". 31eda6f7c3/src/cargo/core/compiler/build_context/target_info.rs (L242)
-----
cc `@dtolnay`
r? `@jackh726`
Description of the `PATH` option:
> A filepath may optionally be specified for each requested information
> kind, in the format `--print KIND=PATH`, just like for `--emit`. When
> a path is specified, information will be written there instead of to
> stdout.
Implement refinement lint for RPITIT
Implements a lint that warns against accidentally refining an RPITIT in an implementation. This is not a hard error, and can be suppressed with `#[allow(refining_impl_trait)]`, since this behavior may be desirable -- the lint just serves as an acknowledgement from the impl author that they understand that the types they write in the implementation are an API guarantee.
This compares bounds syntactically, not semantically -- semantic implication is more difficult and essentially relies on adding the ability to keep the RPITIT hidden in the trait system so that things can be proven about the type that shows up in the impl without its own bounds leaking through, either via a new reveal mode or something else. This was experimentally implemented in #111931.
Somewhat opinionated choices:
1. Putting the lint behind `refining_impl_trait` rather than a blanket `refine` lint. This could be changed, but I like keeping the lint specialized to RPITITs so the explanation can be tailored to it.
2. This PR does not include the `#[refine]` attribute or the feature gate, since it's kind of orthogonal and can be added in a separate PR.
r? `@oli-obk`
Guillaume Gomez