Add help note to unconstrained const parameter
Resolves#68366, since it is currently intended behaviour.
If demonstrating `T -> U` is injective, there should be an additional word that it is not **yet** supported.
r? @lcnr
Add derive macro for specifying diagnostics using attributes.
Introduces `#[derive(SessionDiagnostic)]`, a derive macro for specifying structs that can be converted to Diagnostics using directions given by attributes on the struct and its fields. Currently, the following attributes have been implemented:
- `#[code = "..."]` -- this sets the Diagnostic's error code, and must be provided on the struct iself (ie, not on a field). Equivalent to calling `code`.
- `#[message = "..."]` -- this sets the Diagnostic's primary error message.
- `#[label = "..."]` -- this must be applied to fields of type `Span`, and is equivalent to `span_label`
- `#[suggestion(..)]` -- this allows a suggestion message to be supplied. This attribute must be applied to a field of type `Span` or `(Span, Applicability)`, and is equivalent to calling `span_suggestion`. Valid arguments are:
- `message = "..."` -- this sets the suggestion message.
- (Optional) `code = "..."` -- this suggests code for the suggestion. Defaults to empty.
`suggestion`also comes with other variants: `#[suggestion_short(..)]`, `#[suggestion_hidden(..)]` and `#[suggestion_verbose(..)]` which all take the same keys.
Within the strings passed to each attribute, fields can be referenced without needing to be passed explicitly into the format string -- eg, `#[error = "{ident} already declared"] ` will set the error message to `format!("{} already declared", &self.ident)`. Any fields on the struct can be referenced in this way.
Additionally, for any of these attributes, Option fields can be used to only optionally apply the decoration -- for example:
```rust
#[derive(SessionDiagnostic)]
#[code = "E0123"]
struct SomeKindOfError {
...
#[suggestion(message = "informative error message")]
opt_sugg: Option<(Span, Applicability)>
...
}
```
will not emit a suggestion if `opt_sugg` is `None`.
We plan on iterating on this macro further; this PR is a start.
Closes#61132.
r? `@oli-obk`
do not apply DerefMut on union field
This implements the part of [RFC 2514](https://github.com/rust-lang/rfcs/blob/master/text/2514-union-initialization-and-drop.md) about `DerefMut`. Unlike described in the RFC, we only apply this warning specifically when doing `DerefMut` of a `ManuallyDrop` field; that is really the case we are worried about here.
@matthewjasper suggested I patch `convert_place_derefs_to_mutable` and `convert_place_op_to_mutable` for this, but I could not find anything to do in `convert_place_op_to_mutable` and this is sufficient to make the test pass. However, maybe there are some other cases this misses? I have no familiarity with this code.
This is a breaking change *in theory*, if someone used `ManuallyDrop<T>` in a union field and relied on automatic `DerefMut`. But on stable this means `T: Copy`, so the `ManuallyDrop` is rather pointless.
Cc https://github.com/rust-lang/rust/issues/55149
While formatting for user diagnostics used `Display` for all most cases,
some small amount of cases used `Debug` instead. Until now, `Display`
and `Debug` yielded the same output for many types. However, with path
trimming, we want to show a shorter path for the user, these cases need
fixing.
