Prefer DiagnosticBuilder over Diagnostic in diagnostic modifiers.

There are lots of functions that modify a diagnostic. This can be via a
`&mut Diagnostic` or a `&mut DiagnosticBuilder`, because the latter type
wraps the former and impls `DerefMut`.

This commit converts all the `&mut Diagnostic` occurrences to `&mut
DiagnosticBuilder`. This is a step towards greatly simplifying
`Diagnostic`. Some of the relevant function are made generic, because
they deal with both errors and warnings. No function bodies are changed,
because all the modifier methods are available on both `Diagnostic` and
`DiagnosticBuilder`.

compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs

@@ -1,5 +1,5 @@
 use crate::structured_errors::StructuredDiagnostic;
-use rustc_errors::{codes::*, pluralize, Applicability, Diagnostic, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{codes::*, pluralize, Applicability, DiagnosticBuilder, MultiSpan};
 use rustc_hir as hir;
 use rustc_middle::ty::{self as ty, AssocItems, AssocKind, TyCtxt};
 use rustc_session::Session;
@@ -525,7 +525,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     }
 
     /// Builds the `expected 1 type argument / supplied 2 type arguments` message.
-    fn notify(&self, err: &mut Diagnostic) {
+    fn notify(&self, err: &mut DiagnosticBuilder<'_>) {
         let (quantifier, bound) = self.get_quantifier_and_bound();
         let provided_args = self.num_provided_args();
 
@@ -577,7 +577,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         }
     }
 
-    fn suggest(&self, err: &mut Diagnostic) {
+    fn suggest(&self, err: &mut DiagnosticBuilder<'_>) {
         debug!(
             "suggest(self.provided {:?}, self.gen_args.span(): {:?})",
             self.num_provided_args(),
@@ -605,7 +605,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     /// ```text
     /// type Map = HashMap<String>;
     /// ```
-    fn suggest_adding_args(&self, err: &mut Diagnostic) {
+    fn suggest_adding_args(&self, err: &mut DiagnosticBuilder<'_>) {
         if self.gen_args.parenthesized != hir::GenericArgsParentheses::No {
             return;
         }
@@ -624,7 +624,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         }
     }
 
-    fn suggest_adding_lifetime_args(&self, err: &mut Diagnostic) {
+    fn suggest_adding_lifetime_args(&self, err: &mut DiagnosticBuilder<'_>) {
         debug!("suggest_adding_lifetime_args(path_segment: {:?})", self.path_segment);
         let num_missing_args = self.num_missing_lifetime_args();
         let num_params_to_take = num_missing_args;
@@ -678,7 +678,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         }
     }
 
-    fn suggest_adding_type_and_const_args(&self, err: &mut Diagnostic) {
+    fn suggest_adding_type_and_const_args(&self, err: &mut DiagnosticBuilder<'_>) {
         let num_missing_args = self.num_missing_type_or_const_args();
         let msg = format!("add missing {} argument{}", self.kind(), pluralize!(num_missing_args));
 
@@ -738,7 +738,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     /// ```compile_fail
     /// Into::into::<Option<_>>(42) // suggests considering `Into::<Option<_>>::into(42)`
     /// ```
-    fn suggest_moving_args_from_assoc_fn_to_trait(&self, err: &mut Diagnostic) {
+    fn suggest_moving_args_from_assoc_fn_to_trait(&self, err: &mut DiagnosticBuilder<'_>) {
         let trait_ = match self.tcx.trait_of_item(self.def_id) {
             Some(def_id) => def_id,
             None => return,
@@ -794,7 +794,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
 
     fn suggest_moving_args_from_assoc_fn_to_trait_for_qualified_path(
         &self,
-        err: &mut Diagnostic,
+        err: &mut DiagnosticBuilder<'_>,
         qpath: &'tcx hir::QPath<'tcx>,
         msg: String,
         num_assoc_fn_excess_args: usize,
@@ -827,7 +827,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
 
     fn suggest_moving_args_from_assoc_fn_to_trait_for_method_call(
         &self,
-        err: &mut Diagnostic,
+        err: &mut DiagnosticBuilder<'_>,
         trait_def_id: DefId,
         expr: &'tcx hir::Expr<'tcx>,
         msg: String,
@@ -881,7 +881,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     /// ```text
     /// type Map = HashMap<String, String, String, String>;
     /// ```
-    fn suggest_removing_args_or_generics(&self, err: &mut Diagnostic) {
+    fn suggest_removing_args_or_generics(&self, err: &mut DiagnosticBuilder<'_>) {
         let num_provided_lt_args = self.num_provided_lifetime_args();
         let num_provided_type_const_args = self.num_provided_type_or_const_args();
         let unbound_types = self.get_unbound_associated_types();
@@ -899,7 +899,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         let provided_args_matches_unbound_traits =
             unbound_types.len() == num_redundant_type_or_const_args;
 
-        let remove_lifetime_args = |err: &mut Diagnostic| {
+        let remove_lifetime_args = |err: &mut DiagnosticBuilder<'_>| {
             let mut lt_arg_spans = Vec::new();
             let mut found_redundant = false;
             for arg in self.gen_args.args {
@@ -940,7 +940,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
             );
         };
 
-        let remove_type_or_const_args = |err: &mut Diagnostic| {
+        let remove_type_or_const_args = |err: &mut DiagnosticBuilder<'_>| {
             let mut gen_arg_spans = Vec::new();
             let mut found_redundant = false;
             for arg in self.gen_args.args {
@@ -1037,7 +1037,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     }
 
     /// Builds the `type defined here` message.
-    fn show_definition(&self, err: &mut Diagnostic) {
+    fn show_definition(&self, err: &mut DiagnosticBuilder<'_>) {
         let mut spans: MultiSpan = if let Some(def_span) = self.tcx.def_ident_span(self.def_id) {
             if self.tcx.sess.source_map().is_span_accessible(def_span) {
                 def_span.into()
@@ -1088,7 +1088,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     }
 
     /// Add note if `impl Trait` is explicitly specified.
-    fn note_synth_provided(&self, err: &mut Diagnostic) {
+    fn note_synth_provided(&self, err: &mut DiagnosticBuilder<'_>) {
         if !self.is_synth_provided() {
             return;
         }