Rollup merge of #100351 - compiler-errors:diagnostic-convention, r=fee1-dead

Use `&mut Diagnostic` instead of `&mut DiagnosticBuilder` unless needed

This seems to be the established convention (02ff9e0) when `DiagnosticBuilder` was first added. I am guilty of introducing some of these.

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -19,7 +19,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
     fluent, Applicability, DiagnosticBuilder, DiagnosticMessage, Handler, MultiSpan, PResult,
 };
-use rustc_errors::{pluralize, struct_span_err, Diagnostic, EmissionGuarantee, ErrorGuaranteed};
+use rustc_errors::{pluralize, struct_span_err, Diagnostic, ErrorGuaranteed};
 use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, Ident};
@@ -228,13 +228,13 @@ struct MultiSugg {
 }
 
 impl MultiSugg {
-    fn emit<G: EmissionGuarantee>(self, err: &mut DiagnosticBuilder<'_, G>) {
+    fn emit(self, err: &mut Diagnostic) {
         err.multipart_suggestion(&self.msg, self.patches, self.applicability);
     }
 
     /// Overrides individual messages and applicabilities.
-    fn emit_many<G: EmissionGuarantee>(
-        err: &mut DiagnosticBuilder<'_, G>,
+    fn emit_many(
+        err: &mut Diagnostic,
         msg: &str,
         applicability: Applicability,
         suggestions: impl Iterator<Item = Self>,

compiler/rustc_parse/src/parser/expr.rs

@@ -859,7 +859,7 @@ impl<'a> Parser<'a> {
             );
             let mut err = self.struct_span_err(span, &msg);
 
-            let suggest_parens = |err: &mut DiagnosticBuilder<'_, _>| {
+            let suggest_parens = |err: &mut Diagnostic| {
                 let suggestions = vec![
                     (span.shrink_to_lo(), "(".to_string()),
                     (span.shrink_to_hi(), ")".to_string()),