diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
index 8ad40c0aa0a5d..7457369aa58cb 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
@@ -1,6 +1,4 @@
-use rustc_errors::{
-    Applicability, Diagnostic, DiagnosticBuilder, EmissionGuarantee, ErrorGuaranteed,
-};
+use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir as hir;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::Node;
@@ -629,25 +627,20 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         self.buffer_error(err);
     }
 
-    fn suggest_map_index_mut_alternatives(
-        &self,
-        ty: Ty<'_>,
-        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
-        span: Span,
-    ) {
+    fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diagnostic, span: Span) {
         let Some(adt) = ty.ty_adt_def() else { return };
         let did = adt.did();
         if self.infcx.tcx.is_diagnostic_item(sym::HashMap, did)
             || self.infcx.tcx.is_diagnostic_item(sym::BTreeMap, did)
         {
-            struct V<'a, 'b, 'tcx, G: EmissionGuarantee> {
+            struct V<'a, 'tcx> {
                 assign_span: Span,
-                err: &'a mut DiagnosticBuilder<'b, G>,
+                err: &'a mut Diagnostic,
                 ty: Ty<'tcx>,
                 suggested: bool,
             }
-            impl<'a, 'b: 'a, 'hir, 'tcx, G: EmissionGuarantee> Visitor<'hir> for V<'a, 'b, 'tcx, G> {
-                fn visit_stmt(&mut self, stmt: &'hir hir::Stmt<'hir>) {
+            impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> {
+                fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
                     hir::intravisit::walk_stmt(self, stmt);
                     let expr = match stmt.kind {
                         hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr,
@@ -705,7 +698,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                                     ),
                                     (rv.span.shrink_to_hi(), ")".to_string()),
                                 ],
-                            ].into_iter(),
+                            ],
                             Applicability::MachineApplicable,
                         );
                         self.suggested = true;
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 45c017df918e8..e83e10a68c325 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -717,7 +717,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<SubdiagnosticMessage>,
-        suggestions: impl Iterator<Item = String>,
+        suggestions: impl IntoIterator<Item = String>,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestions_with_style(
@@ -734,11 +734,11 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<SubdiagnosticMessage>,
-        suggestions: impl Iterator<Item = String>,
+        suggestions: impl IntoIterator<Item = String>,
         applicability: Applicability,
         style: SuggestionStyle,
     ) -> &mut Self {
-        let mut suggestions: Vec<_> = suggestions.collect();
+        let mut suggestions: Vec<_> = suggestions.into_iter().collect();
         suggestions.sort();
 
         debug_assert!(
@@ -765,10 +765,10 @@ impl Diagnostic {
     pub fn multipart_suggestions(
         &mut self,
         msg: impl Into<SubdiagnosticMessage>,
-        suggestions: impl Iterator<Item = Vec<(Span, String)>>,
+        suggestions: impl IntoIterator<Item = Vec<(Span, String)>>,
         applicability: Applicability,
     ) -> &mut Self {
-        let suggestions: Vec<_> = suggestions.collect();
+        let suggestions: Vec<_> = suggestions.into_iter().collect();
         debug_assert!(
             !(suggestions
                 .iter()
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index 730061fca9936..18cbf963494fc 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -599,13 +599,13 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         &mut self,
         sp: Span,
         msg: impl Into<SubdiagnosticMessage>,
-        suggestions: impl Iterator<Item = String>,
+        suggestions: impl IntoIterator<Item = String>,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn multipart_suggestions(
         &mut self,
         msg: impl Into<SubdiagnosticMessage>,
-        suggestions: impl Iterator<Item = Vec<(Span, String)>>,
+        suggestions: impl IntoIterator<Item = Vec<(Span, String)>>,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn span_suggestion_short(
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 2a8512acf8cfa..3a67c032b3bdd 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -401,7 +401,7 @@ impl<'a> Parser<'a> {
                 .span_suggestions(
                     span.shrink_to_hi(),
                     "add `mut` or `const` here",
-                    ["mut ".to_string(), "const ".to_string()].into_iter(),
+                    ["mut ".to_string(), "const ".to_string()],
                     Applicability::HasPlaceholders,
                 )
                 .emit();
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs
index c6fe40f72fc63..c181de48a9ad8 100644
--- a/compiler/rustc_passes/src/liveness.rs
+++ b/compiler/rustc_passes/src/liveness.rs
@@ -87,6 +87,7 @@ use self::VarKind::*;
 use rustc_ast::InlineAsmOptions;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::Applicability;
+use rustc_errors::Diagnostic;
 use rustc_hir as hir;
 use rustc_hir::def::*;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -1690,7 +1691,7 @@ impl<'tcx> Liveness<'_, 'tcx> {
         &self,
         name: &str,
         opt_body: Option<&hir::Body<'_>>,
-        err: &mut rustc_errors::DiagnosticBuilder<'_, ()>,
+        err: &mut Diagnostic,
     ) -> bool {
         let mut has_litstring = false;
         let Some(opt_body) = opt_body else {return false;};
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index a1338dcd4771b..cdc28db13f3ac 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -437,7 +437,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
     fn try_lookup_name_relaxed(
         &mut self,
-        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        err: &mut Diagnostic,
         source: PathSource<'_>,
         path: &[Segment],
         span: Span,
@@ -497,7 +497,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                         .contains(span)
                     {
                         // Already reported this issue on the lhs of the type ascription.
-                        err.delay_as_bug();
+                        err.downgrade_to_delayed_bug();
                         return (true, candidates);
                     }
                 }
@@ -616,7 +616,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
     fn suggest_trait_and_bounds(
         &mut self,
-        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        err: &mut Diagnostic,
         source: PathSource<'_>,
         res: Option<Res>,
         span: Span,
@@ -691,7 +691,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
     fn suggest_typo(
         &mut self,
-        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        err: &mut Diagnostic,
         source: PathSource<'_>,
         path: &[Segment],
         span: Span,
@@ -750,7 +750,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
     fn err_code_special_cases(
         &mut self,
-        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        err: &mut Diagnostic,
         source: PathSource<'_>,
         path: &[Segment],
         span: Span,
@@ -1941,7 +1941,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 err.span_suggestions(
                     span,
                     &msg,
-                    suggestable_variants.into_iter(),
+                    suggestable_variants,
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -1995,7 +1995,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 err.span_suggestions(
                     span,
                     msg,
-                    suggestable_variants.into_iter(),
+                    suggestable_variants,
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -2025,7 +2025,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 err.span_suggestions(
                     span,
                     msg,
-                    suggestable_variants_with_placeholders.into_iter(),
+                    suggestable_variants_with_placeholders,
                     Applicability::HasPlaceholders,
                 );
             }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 0f4aa87b43f5e..d573229f71714 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -1117,7 +1117,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         err.span_suggestions(
                             span.shrink_to_lo(),
                             "consider borrowing here",
-                            ["&".to_string(), "&mut ".to_string()].into_iter(),
+                            ["&".to_string(), "&mut ".to_string()],
                             Applicability::MaybeIncorrect,
                         );
                     } else {