Auto merge of #75138 - jumbatm:session-diagnostic-derive, r=oli-obk

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`

Author: bors

Cargo.lock

@@ -4087,6 +4087,7 @@ dependencies = [
  "rustc_hir_pretty",
  "rustc_index",
  "rustc_infer",
+ "rustc_macros",
  "rustc_middle",
  "rustc_session",
  "rustc_span",

compiler/rustc_error_codes/src/error_codes/E0224.md

@@ -1,4 +1,4 @@
-A trait object was declaired with no traits.
+A trait object was declared with no traits.
 
 Erroneous code example:
 
@@ -8,7 +8,7 @@ type Foo = dyn 'static +;
 
 Rust does not currently support this.
 
-To solve ensure the the trait object has at least one trait:
+To solve, ensure that the trait object has at least one trait:
 
 ```
 type Foo = dyn 'static + Copy;

compiler/rustc_macros/src/lib.rs

@@ -1,3 +1,4 @@
+#![feature(proc_macro_diagnostic)]
 #![allow(rustc::default_hash_types)]
 #![recursion_limit = "128"]
 
@@ -9,6 +10,7 @@ mod hash_stable;
 mod lift;
 mod query;
 mod serialize;
+mod session_diagnostic;
 mod symbols;
 mod type_foldable;
 
@@ -36,3 +38,14 @@ decl_derive!([MetadataDecodable] => serialize::meta_decodable_derive);
 decl_derive!([MetadataEncodable] => serialize::meta_encodable_derive);
 decl_derive!([TypeFoldable, attributes(type_foldable)] => type_foldable::type_foldable_derive);
 decl_derive!([Lift, attributes(lift)] => lift::lift_derive);
+decl_derive!(
+    [SessionDiagnostic, attributes(
+        message,
+        lint,
+        error,
+        label,
+        suggestion,
+        suggestion_short,
+        suggestion_hidden,
+        suggestion_verbose)] => session_diagnostic::session_diagnostic_derive
+);