fix clippy::useless_format

compiler/rustc_hir_analysis/src/coherence/orphan.rs

@@ -352,7 +352,7 @@ fn emit_orphan_check_error<'tcx>(
 
                 let this = |name: &str| {
                     if !trait_ref.def_id.is_local() && !is_target_ty {
-                        msg("this", &format!(" because this is a foreign trait"))
+                        msg("this", " because this is a foreign trait")
                     } else {
                         msg("this", &format!(" because {name} are always foreign"))
                     }

compiler/rustc_hir_typeck/src/cast.rs

@@ -705,10 +705,10 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                 )
             }),
             |lint| {
-                lint.help(format!(
+                lint.help(
                     "cast can be replaced by coercion; this might \
-                     require a temporary variable"
+                     require a temporary variable",
-                ))
+                )
             },
         );
     }

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -264,11 +264,11 @@ fn msg_span_from_named_region<'tcx>(
         ty::RePlaceholder(ty::PlaceholderRegion {
             bound: ty::BoundRegion { kind: ty::BoundRegionKind::BrAnon(Some(span)), .. },
             ..
-        }) => (format!("the anonymous lifetime defined here"), Some(span)),
+        }) => ("the anonymous lifetime defined here".to_owned(), Some(span)),
         ty::RePlaceholder(ty::PlaceholderRegion {
             bound: ty::BoundRegion { kind: ty::BoundRegionKind::BrAnon(None), .. },
             ..
-        }) => (format!("an anonymous lifetime"), None),
+        }) => ("an anonymous lifetime".to_owned(), None),
         _ => bug!("{:?}", region),
     }
 }
@@ -2354,7 +2354,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                     if let Ok(snip) = self.tcx.sess.source_map().span_to_next_source(p.span)
                                         && snip.starts_with(' ')
                                     {
-                                        format!("{new_lt}")
+                                        new_lt.to_string()
                                     } else {
                                         format!("{new_lt} ")
                                     }

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -333,11 +333,7 @@ pub fn suggest_new_region_bound(
                     } else {
                         None
                     };
-                    let name = if let Some(name) = &existing_lt_name {
+                    let name = if let Some(name) = &existing_lt_name { name } else { "'a" };
-                        format!("{}", name)
-                    } else {
-                        format!("'a")
-                    };
                     // if there are more than one elided lifetimes in inputs, the explicit `'_` lifetime cannot be used.
                     // introducing a new lifetime `'a` or making use of one from existing named lifetimes if any
                     if let Some(id) = scope_def_id
@@ -350,7 +346,7 @@ pub fn suggest_new_region_bound(
                                   if p.span.hi() - p.span.lo() == rustc_span::BytePos(1) { // Ampersand (elided without '_)
                                       (p.span.shrink_to_hi(),format!("{name} "))
                                   } else { // Underscore (elided with '_)
-                                      (p.span, format!("{name}"))
+                                      (p.span, name.to_string())
                                   }
                             )
                             .collect::<Vec<_>>()

compiler/rustc_resolve/src/diagnostics.rs

@@ -1395,7 +1395,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             let head_span = source_map.guess_head_span(span);
             err.subdiagnostic(ConsiderAddingADerive {
                 span: head_span.shrink_to_lo(),
-                suggestion: format!("#[derive(Default)]\n")
+                suggestion: "#[derive(Default)]\n".to_string(),
             });
         }
         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
@@ -1718,7 +1718,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             if next_binding.is_none() && let Some(span) = non_exhaustive {
                 note_span.push_span_label(
                     span,
-                    format!("cannot be constructed because it is `#[non_exhaustive]`"),
+                    "cannot be constructed because it is `#[non_exhaustive]`",
                 );
             }
             err.span_note(note_span, msg);

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1471,7 +1471,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
                         let span = if needs_parens { span } else { span.shrink_to_lo() };
                         let suggestions = if !needs_parens {
-                            vec![(span.shrink_to_lo(), format!("{}", sugg_prefix))]
+                            vec![(span.shrink_to_lo(), sugg_prefix)]
                         } else {
                             vec![
                                 (span.shrink_to_lo(), format!("{}(", sugg_prefix)),