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r=compiler-errors
Forbid borrows and unsized types from being used as the type of a const generic under `adt_const_params`
Fixes #112219
Fixes #112124
Fixes #112125
### Motivation
Currently the `adt_const_params` feature allows writing `Foo<const N: [u8]>` this is entirely useless as it is not possible to write an expression which evaluates to a type that is not `Sized`. In order to actually use unsized types in const generics they are typically written as `const N: &[u8]` which *is* possible to provide a value of.
Unfortunately allowing the types of const parameters to contain references is non trivial (#120961) as it introduces a number of difficult questions about how equality of references in the type system should behave. References in the types of const generics is largely only useful for using unsized types in const generics.
This PR introduces a new feature gate `unsized_const_parameters` and moves support for `const N: [u8]` and `const N: &...` from `adt_const_params` into it. The goal here hopefully is to experiment with allowing `const N: [u8]` to work without references and then eventually completely forbid references in const generics.
Splitting this out into a new feature gate means that stabilization of `adt_const_params` does not have to resolve #120961 which is the only remaining "big" blocker for the feature. Remaining issues after this are a few ICEs and naming bikeshed for `ConstParamTy`.
### Implementation
The implementation is slightly subtle here as we would like to ensure that a stabilization of `adt_const_params` is forwards compatible with any outcome of `unsized_const_parameters`. This is inherently tricky as we do not support unstable trait implementations and we determine whether a type is valid as the type of a const parameter via a trait bound.
There are a few constraints here:
- We would like to *allow for the possibility* of adding a `Sized` supertrait to `ConstParamTy` in the event that we wind up opting to not support unsized types and instead requiring people to write the 'sized version', e.g. `const N: [u8; M]` instead of `const N: [u8]`.
- Crates should be able to enable `unsized_const_parameters` and write trait implementations of `ConstParamTy` for `!Sized` types without downstream crates that only enable `adt_const_params` being able to observe this (required for std to be able to `impl<T> ConstParamTy for [T]`
Ultimately the way this is accomplished is via having two traits (sad), `ConstParamTy` and `UnsizedConstParamTy`. Depending on whether `unsized_const_parameters` is enabled or not we change which trait is used to check whether a type is allowed to be a const parameter.
Long term (when stabilizing `UnsizedConstParamTy`) it should be possible to completely merge these traits (and derive macros), only having a single `trait ConstParamTy` and `macro ConstParamTy`.
Under `adt_const_params` it is now illegal to directly refer to `ConstParamTy` it is only used as an internal impl detail by `derive(ConstParamTy)` and checking const parameters are well formed. This is necessary in order to ensure forwards compatibility with all possible future directions for `feature(unsized_const_parameters)`.
Generally the intuition here should be that `ConstParamTy` is the stable trait that everything uses, and `UnsizedConstParamTy` is that plus unstable implementations (well, I suppose `ConstParamTy` isn't stable yet :P).
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When encountering `-> Trait`, suggest `-> Box<dyn Trait>` (instead of `-> Box<Trait>`.
If there's a single returned type within the `fn`, suggest `-> impl Trait`.
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No longer track "zero-width" chars in `SourceMap`, read directly from the line when calculating the `display_col` of a `BytePos`. Move `char_width` to `rustc_span` and use it from the emitter.
This change allows the following to properly align in terminals (depending on the font, the replaced control codepoints are rendered as 1 or 2 width, on my terminal they are rendered as 1, on VSCode text they are rendered as 2):
```
error: this file contains an unclosed delimiter
--> $DIR/issue-68629.rs:5:17
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LL | ␜␟ts␀![{i
| -- unclosed delimiter
| |
| unclosed delimiter
LL | ␀␀ fn rݻoa>rݻm
| ^
```
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Accurate `use` rename suggestion span
When suggesting to rename an import with `as`, use a smaller span to render the suggestion with a better format:
```
error[E0252]: the name `baz` is defined multiple times
--> $DIR/issue-25396.rs:4:5
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LL | use foo::baz;
| -------- previous import of the module `baz` here
LL | use bar::baz;
| ^^^^^^^^ `baz` reimported here
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= note: `baz` must be defined only once in the type namespace of this module
help: you can use `as` to change the binding name of the import
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LL | use bar::baz as other_baz;
| ++++++++++++
```
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Fix associated item removal suggestion
We were previously telling people to write what was already there, instead of removal (treating it as a `help`). We now properly suggest to remove the code that needs to be removed.
```
error[E0229]: associated item constraints are not allowed here
--> $DIR/E0229.rs:13:25
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LL | fn baz<I>(x: &<I as Foo<A = Bar>>::A) {}
| ^^^^^^^ associated item constraint not allowed here
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help: consider removing this associated item binding
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LL - fn baz<I>(x: &<I as Foo<A = Bar>>::A) {}
LL + fn baz<I>(x: &<I as Foo>::A) {}
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```
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When suggesting to rename an import with `as`, use a smaller span to
render the suggestion with a better format:
```
error[E0252]: the name `baz` is defined multiple times
--> $DIR/issue-25396.rs:4:5
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LL | use foo::baz;
| -------- previous import of the module `baz` here
LL | use bar::baz;
| ^^^^^^^^ `baz` reimported here
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= note: `baz` must be defined only once in the type namespace of this module
help: you can use `as` to change the binding name of the import
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LL | use bar::baz as other_baz;
| ++++++++++++
```
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We were previously telling people to write what was already there, instead of removal.
```
error[E0229]: associated item constraints are not allowed here
--> $DIR/E0229.rs:13:25
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LL | fn baz<I>(x: &<I as Foo<A = Bar>>::A) {}
| ^^^^^^^ associated item constraint not allowed here
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help: consider removing this associated item binding
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LL - fn baz<I>(x: &<I as Foo<A = Bar>>::A) {}
LL + fn baz<I>(x: &<I as Foo>::A) {}
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```
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Use ordinal number in argument error
Add an ordinal number to two argument errors ("unexpected" and "missing") for ease of understanding error.
```
error[E0061]: this function takes 3 arguments but 2 arguments were supplied
--> test.rs:11:5
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11 | f(42, 'a');
| ^ --- 2nd argument of type `f32` is missing
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(snip)
error[E0061]: this function takes 3 arguments but 4 arguments were supplied
--> test.rs:12:5
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12 | f(42, 42, 1.0, 'a');
| ^ ----
| | |
| | unexpected 2nd argument of type `{integer}`
| help: remove the extra argument
```
To get an ordinal number, I copied `ordinalize` from other crate `rustc_resolve` because I think it is too much to link `rustc_resolve` for this small function. Please let me know if there is a better way.
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Make parse error suggestions verbose and fix spans
Go over all structured parser suggestions and make them verbose style.
When suggesting to add or remove delimiters, turn them into multiple suggestion parts.
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Fix error message
Fix tests
Format
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Go over all structured parser suggestions and make them verbose style.
When suggesting to add or remove delimiters, turn them into multiple suggestion parts.
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Let's `#[expect]` some lints: Stabilize `lint_reasons` (RFC 2383)
Let's give this another try! The [previous stabilization attempt](https://github.com/rust-lang/rust/pull/99063) was stalled by some unresolved questions. These have been discussed in a [lang team](https://github.com/rust-lang/lang-team/issues/191) meeting. The last open question, regarding the semantics of the `#[expect]` attribute was decided on in https://github.com/rust-lang/rust/issues/115980
I've just updated the [stabilization report](https://github.com/rust-lang/rust/issues/54503#issuecomment-1179563964) with the discussed questions and decisions. Luckily, the decision is inline with the current implementation.
This hopefully covers everything. Let's hope that the CI will be green like the spring.
fixes #115980
fixes #54503
---
r? `@wesleywiser`
Tacking Issue: https://github.com/rust-lang/rust/issues/54503
Stabilization Report: https://github.com/rust-lang/rust/issues/54503#issuecomment-1179563964
Documentation Update: https://github.com/rust-lang/reference/pull/1237
<!--
For Clippy:
changelog: [`allow_attributes`]: Is now available on stable, since the `lint_reasons` feature was stabilized
changelog: [`allow_attributes_without_reason`]: Is now available on stable, since the `lint_reasons` feature was stabilized
-->
---
Roses are red,
Violets are blue,
Let's expect lints,
With reason clues
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Change E0369 to give note informations for foreign items.
Change E0369 to give note informations for foreign items.
Make it easy for developers to understand why the binop cannot be applied.
fixes #125631
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Make it easy for developers to understand why the binop cannot be applied.
fixes #125631
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```
error[E0382]: use of moved value: `t`
--> $DIR/use_of_moved_value_copy_suggestions.rs:7:9
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LL | fn duplicate_t<T>(t: T) -> (T, T) {
| - move occurs because `t` has type `T`, which does not implement the `Copy` trait
...
LL | (t, t)
| - ^ value used here after move
| |
| value moved here
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help: if `T` implemented `Clone`, you could clone the value
--> $DIR/use_of_moved_value_copy_suggestions.rs:4:16
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LL | fn duplicate_t<T>(t: T) -> (T, T) {
| ^ consider constraining this type parameter with `Clone`
...
LL | (t, t)
| - you could clone this value
help: consider restricting type parameter `T`
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LL | fn duplicate_t<T: Copy>(t: T) -> (T, T) {
| ++++++
```
The `help` is new. On ADTs, we also extend the output with span labels:
```
error[E0507]: cannot move out of static item `FOO`
--> $DIR/issue-17718-static-move.rs:6:14
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LL | let _a = FOO;
| ^^^ move occurs because `FOO` has type `Foo`, which does not implement the `Copy` trait
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note: if `Foo` implemented `Clone`, you could clone the value
--> $DIR/issue-17718-static-move.rs:1:1
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LL | struct Foo;
| ^^^^^^^^^^ consider implementing `Clone` for this type
...
LL | let _a = FOO;
| --- you could clone this value
help: consider borrowing here
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LL | let _a = &FOO;
| +
```
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Suggest using type args directly instead of equality constraint
When type arguments are written erroneously using an equality constraint we suggest specifying them directly without the equality constraint.
Fixes #122162
Changes the diagnostic in the issue from:
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
| ^^^^^^^ associated type not allowed here
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```
to
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
| ^^^^^^^ associated type not allowed here
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help: to use `T` as a generic argument specify it directly
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| impl std::cmp::PartialEq<T> for S {
| ~
```
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weak lang items are not allowed to be #[track_caller]
For instance the panic handler will be called via this import
```rust
extern "Rust" {
#[lang = "panic_impl"]
fn panic_impl(pi: &PanicInfo<'_>) -> !;
}
```
A `#[track_caller]` would add an extra argument and thus make this the wrong signature.
The 2nd commit is a consistency rename; based on the docs [here](https://doc.rust-lang.org/unstable-book/language-features/lang-items.html) and [here](https://rustc-dev-guide.rust-lang.org/lang-items.html) I figured "lang item" is more widely used. (In the compiler output, "lang item" and "language item" seem to be pretty even.)
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Silence some follow-up errors on trait impls in case the trait has conflicting or otherwise incoherent impls
fixes #123292
Also removes a bunch of extra diagnostics that were introduced in https://github.com/rust-lang/rust/pull/121154 and https://github.com/rust-lang/rust/pull/120558
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Detect borrow checker errors where `.clone()` would be an appropriate user action
When a value is moved twice, suggest cloning the earlier move:
```
error[E0509]: cannot move out of type `U2`, which implements the `Drop` trait
--> $DIR/union-move.rs:49:18
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LL | move_out(x.f1_nocopy);
| ^^^^^^^^^^^
| |
| cannot move out of here
| move occurs because `x.f1_nocopy` has type `ManuallyDrop<RefCell<i32>>`, which does not implement the `Copy` trait
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help: consider cloning the value if the performance cost is acceptable
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LL | move_out(x.f1_nocopy.clone());
| ++++++++
```
When a value is borrowed by an `fn` call, consider if cloning the result of the call would be reasonable, and suggest cloning that, instead of the argument:
```
error[E0505]: cannot move out of `a` because it is borrowed
--> $DIR/variance-issue-20533.rs:53:14
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LL | let a = AffineU32(1);
| - binding `a` declared here
LL | let x = bat(&a);
| -- borrow of `a` occurs here
LL | drop(a);
| ^ move out of `a` occurs here
LL | drop(x);
| - borrow later used here
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help: consider cloning the value if the performance cost is acceptable
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LL | let x = bat(&a).clone();
| ++++++++
```
otherwise, suggest cloning the argument:
```
error[E0505]: cannot move out of `a` because it is borrowed
--> $DIR/variance-issue-20533.rs:59:14
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LL | let a = ClonableAffineU32(1);
| - binding `a` declared here
LL | let x = foo(&a);
| -- borrow of `a` occurs here
LL | drop(a);
| ^ move out of `a` occurs here
LL | drop(x);
| - borrow later used here
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help: consider cloning the value if the performance cost is acceptable
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LL - let x = foo(&a);
LL + let x = foo(a.clone());
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```
This suggestion doesn't attempt to square out the types between what's cloned and what the `fn` expects, to allow the user to make a determination on whether to change the `fn` call or `fn` definition themselves.
Special case move errors caused by `FnOnce`:
```
error[E0382]: use of moved value: `blk`
--> $DIR/once-cant-call-twice-on-heap.rs:8:5
|
LL | fn foo<F:FnOnce()>(blk: F) {
| --- move occurs because `blk` has type `F`, which does not implement the `Copy` trait
LL | blk();
| ----- `blk` moved due to this call
LL | blk();
| ^^^ value used here after move
|
note: `FnOnce` closures can only be called once
--> $DIR/once-cant-call-twice-on-heap.rs:6:10
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LL | fn foo<F:FnOnce()>(blk: F) {
| ^^^^^^^^ `F` is made to be an `FnOnce` closure here
LL | blk();
| ----- this value implements `FnOnce`, which causes it to be moved when called
```
Account for redundant `.clone()` calls in resulting suggestions:
```
error[E0507]: cannot move out of dereference of `S`
--> $DIR/needs-clone-through-deref.rs:15:18
|
LL | for _ in self.clone().into_iter() {}
| ^^^^^^^^^^^^ ----------- value moved due to this method call
| |
| move occurs because value has type `Vec<usize>`, which does not implement the `Copy` trait
|
note: `into_iter` takes ownership of the receiver `self`, which moves value
--> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
help: you can `clone` the value and consume it, but this might not be your desired behavior
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LL | for _ in <Vec<usize> as Clone>::clone(&self).into_iter() {}
| ++++++++++++++++++++++++++++++ ~
```
We use the presence of `&mut` values in a move error as a proxy for the user caring about side effects, so we don't emit a clone suggestion in that case:
```
error[E0505]: cannot move out of `s` because it is borrowed
--> $DIR/borrowck-overloaded-index-move-index.rs:53:7
|
LL | let mut s = "hello".to_string();
| ----- binding `s` declared here
LL | let rs = &mut s;
| ------ borrow of `s` occurs here
...
LL | f[s] = 10;
| ^ move out of `s` occurs here
...
LL | use_mut(rs);
| -- borrow later used here
```
We properly account for `foo += foo;` errors where we *don't* suggest `foo.clone() += foo;`, instead suggesting `foo += foo.clone();`.
---
Each commit can be reviewed in isolation. There are some "cleanup" commits, but kept them separate in order to show *why* specific changes were being made, and their effect on tests' output.
Fix #49693, CC #64167.
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conflicting or otherwise incoherent impls
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Add help to `hir_analysis_unrecognized_intrinsic_function`
To help remind forgetful people like me what step they forgot.
(If this just ICE'd, https://github.com/rust-lang/compiler-team/issues/620 style, the stack trace would point me here, but since there's a "nice" error that information is lost.)
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To help remind forgetful people like me what step they forgot.
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