Streamline `Diagnostic` proc macro.

First, it is parameterized by the name of the diagnostic and the
DiagCtxt. These are given to `session_diagnostic_derive` and
`lint_diagnostic_derive`. But the names are hard-wired as "diag" and
"handler" (should be "dcx"), and there's no clear reason for the
parameterization. So this commit removes the parameterization and
hard-wires the names internally.

Once that is done `DiagnosticDeriveBuilder` is reduced to a trivial
wrapper around `DiagnosticDeriveKind`, and can be removed.

Also, `DiagnosticDerive` and `LintDiagnosticDerive` don't need the
`builder` field, because it has been reduced to a kind, and they know
their own kind. This avoids the need for some
`let`/`else`/`unreachable!` kind checks

And `DiagnosticDeriveVariantBuilder` no longer needs a lifetime, because
the `parent` field is changed to `kind`, which is now a trivial copy
type.

1 files changed, 2 insertions, 3 deletions

diff --git a/compiler/rustc_macros/src/diagnostics/mod.rs b/compiler/rustc_macros/src/diagnostics/mod.rs
index a536eb3b04e..d3a4e7ba7d1 100644
--- a/compiler/rustc_macros/src/diagnostics/mod.rs
+++ b/compiler/rustc_macros/src/diagnostics/mod.rs
@@ -6,7 +6,6 @@ mod utils;
 
 use diagnostic::{DiagnosticDerive, LintDiagnosticDerive};
 use proc_macro2::TokenStream;
-use quote::format_ident;
 use subdiagnostic::SubdiagnosticDeriveBuilder;
 use synstructure::Structure;
 
@@ -57,7 +56,7 @@ use synstructure::Structure;
 /// See rustc dev guide for more examples on using the `#[derive(Diagnostic)]`:
 /// <https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-structs.html>
 pub fn session_diagnostic_derive(s: Structure<'_>) -> TokenStream {
-    DiagnosticDerive::new(format_ident!("diag"), format_ident!("handler"), s).into_tokens()
+    DiagnosticDerive::new(s).into_tokens()
 }
 
 /// Implements `#[derive(LintDiagnostic)]`, which allows for lints to be specified as a struct,
@@ -103,7 +102,7 @@ pub fn session_diagnostic_derive(s: Structure<'_>) -> TokenStream {
 /// See rustc dev guide for more examples on using the `#[derive(LintDiagnostic)]`:
 /// <https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-structs.html#reference>
 pub fn lint_diagnostic_derive(s: Structure<'_>) -> TokenStream {
-    LintDiagnosticDerive::new(format_ident!("diag"), s).into_tokens()
+    LintDiagnosticDerive::new(s).into_tokens()
 }
 
 /// Implements `#[derive(Subdiagnostic)]`, which allows for labels, notes, helps and