Allow raw identifiers to be used as fluent arguments

compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs

@@ -281,6 +281,8 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
         if should_generate_set_arg(&field) {
             let diag = &self.parent.diag;
             let ident = field.ident.as_ref().unwrap();
+            // strip `r#` prefix, if present
+            let ident = format_ident!("{}", ident);
             return quote! {
                 #diag.set_arg(
                     stringify!(#ident),

compiler/rustc_macros/src/diagnostics/subdiagnostic.rs

@@ -189,6 +189,9 @@ impl<'a> SubdiagnosticDeriveBuilder<'a> {
 
         let diag = &self.diag;
         let ident = ast.ident.as_ref().unwrap();
+        // strip `r#` prefix, if present
+        let ident = format_ident!("{}", ident);
+
         quote! {
             #diag.set_arg(
                 stringify!(#ident),

src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs

@@ -671,3 +671,9 @@ enum ExampleEnum {
     #[diag(typeck::ambiguous_lifetime_bound)]
     Baz,
 }
+
+#[derive(Diagnostic)]
+#[diag(typeck::ambiguous_lifetime_bound, code = "E0123")]
+struct RawIdentDiagnosticArg {
+    pub r#type: String,
+}

src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs

@@ -633,3 +633,11 @@ struct BI {
     #[suggestion_part(code = "")]
     spans: Vec<Span>,
 }
+
+#[derive(Subdiagnostic)]
+#[label(parser::add_paren)]
+struct BJ {
+    #[primary_span]
+    span: Span,
+    r#type: String,
+}