Provide structured suggestion for `#![feature(foo)]`

```
error: `S2<'_>` is forbidden as the type of a const generic parameter
  --> $DIR/lifetime-in-const-param.rs:5:23
   |
LL | struct S<'a, const N: S2>(&'a ());
   |                       ^^
   |
   = note: the only supported types are integers, `bool` and `char`
help: add `#![feature(adt_const_params)]` to the crate attributes to enable more complex and user defined types
   |
LL + #![feature(adt_const_params)]
   |
```

Fix #55941.

1 files changed, 12 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index d523da1ad7e..cfbeac79e50 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -55,6 +55,18 @@ pub struct FeatureDiagnosticHelp {
 }
 
 #[derive(Subdiagnostic)]
+#[suggestion(
+    session_feature_diagnostic_suggestion,
+    applicability = "maybe-incorrect",
+    code = "#![feature({feature})]\n"
+)]
+pub struct FeatureDiagnosticSuggestion {
+    pub feature: Symbol,
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Subdiagnostic)]
 #[help(session_cli_feature_diagnostic_help)]
 pub struct CliFeatureDiagnosticHelp {
     pub feature: Symbol,