more clippy::complexity fixes

redundant_guards
      redundant_slicing
      filter_next
      needless_borrowed_reference
      useless_format

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1701,7 +1701,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
             && !ty.is_never()
         {
             let indentation = if let None = block.expr
-                && let [.., last] = &block.stmts[..]
+                && let [.., last] = &block.stmts
             {
                 tcx.sess.source_map().indentation_before(last.span).unwrap_or_else(String::new)
             } else if let Some(expr) = block.expr {
@@ -1710,7 +1710,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                 String::new()
             };
             if let None = block.expr
-                && let [.., last] = &block.stmts[..]
+                && let [.., last] = &block.stmts
             {
                 err.span_suggestion_verbose(
                     last.span.shrink_to_hi(),
@@ -1750,7 +1750,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                 }
             }
             if let None = block.expr
-                && let [.., last] = &block.stmts[..]
+                && let [.., last] = &block.stmts
             {
                 sugg.push((last.span.shrink_to_hi(), format!("\n{indentation}None")));
             } else if let Some(expr) = block.expr {

compiler/rustc_hir_typeck/src/demand.rs

@@ -862,7 +862,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             mutability,
                         ),
                     ),
-                    match &args[..] {
+                    match &args {
                         [] => (base.span.shrink_to_hi().with_hi(deref.span.hi()), ")".to_string()),
                         [first, ..] => (base.span.between(first.span), ", ".to_string()),
                     },

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

@@ -2452,7 +2452,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
             if !suggs.is_empty() {
                 err.multipart_suggestion_verbose(
-                    format!("{msg}"),
+                    msg,
                     suggs,
                     Applicability::MaybeIncorrect, // Issue #41966
                 );

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -174,7 +174,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         span: Span,
     ) -> Result<PatKind<'tcx>, ErrorGuaranteed> {
         if lo_expr.is_none() && hi_expr.is_none() {
-            let msg = format!("found twice-open range pattern (`..`) outside of error recovery");
+            let msg = "found twice-open range pattern (`..`) outside of error recovery";
             return Err(self.tcx.sess.span_delayed_bug(span, msg));
         }
 

compiler/rustc_resolve/src/imports.rs

@@ -1063,12 +1063,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                             initial_binding.res()
                         });
                         let res = binding.res();
-                        let has_ambiguity_error = this
-                            .ambiguity_errors
-                            .iter()
-                            .filter(|error| !error.warning)
-                            .next()
-                            .is_some();
+                        let has_ambiguity_error =
+                            this.ambiguity_errors.iter().any(|error| !error.warning);
                         if res == Res::Err || has_ambiguity_error {
                             this.tcx
                                 .sess

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1829,13 +1829,12 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             )
             .iter()
             .filter_map(|candidate| candidate.did)
-            .filter(|did| {
+            .find(|did| {
                 self.r
                     .tcx
                     .get_attrs(*did, sym::rustc_diagnostic_item)
                     .any(|attr| attr.value_str() == Some(sym::Default))
-            })
-            .next();
+            });
         let Some(default_trait) = default_trait else {
             return;
         };
@@ -1880,11 +1879,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         };
 
         fields.is_some_and(|fields| {
-            fields
-                .iter()
-                .filter(|vis| !self.r.is_accessible_from(**vis, self.parent_scope.module))
-                .next()
-                .is_some()
+            fields.iter().any(|vis| !self.r.is_accessible_from(*vis, self.parent_scope.module))
         })
     }
 

compiler/rustc_smir/src/rustc_smir/convert/mir.rs

@@ -707,7 +707,7 @@ impl<'tcx> Stable<'tcx> for rustc_middle::mir::Const<'tcx> {
                 let id = tables.intern_const(*self);
                 Const::new(kind, ty, id)
             }
-            mir::Const::Val(val, ty) if matches!(val, mir::ConstValue::ZeroSized) => {
+            mir::Const::Val(mir::ConstValue::ZeroSized, ty) => {
                 let ty = ty.stable(tables);
                 let id = tables.intern_const(*self);
                 Const::new(ConstantKind::ZeroSized, ty, id)

compiler/rustc_trait_selection/src/infer.rs

@@ -101,11 +101,10 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                         self.tcx.impl_trait_ref(impl_def_id).map(|r| (impl_def_id, r))
                     })
                     .map(|(impl_def_id, imp)| (impl_def_id, imp.skip_binder()))
-                    .filter(|(_, imp)| match imp.self_ty().peel_refs().kind() {
+                    .find(|(_, imp)| match imp.self_ty().peel_refs().kind() {
                         ty::Adt(i_def, _) if i_def.did() == def.did() => true,
                         _ => false,
                     })
-                    .next()
             {
                 let mut fulfill_cx = FulfillmentCtxt::new(self);
                 // We get all obligations from the impl to talk about specific

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

@@ -2167,7 +2167,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             })
             .collect();
         err.multipart_suggestion(
-            format!("consider wrapping the function in a closure"),
+            "consider wrapping the function in a closure",
             vec![
                 (arg.span.shrink_to_lo(), format!("|{}| ", closure_names.join(", "))),
                 (arg.span.shrink_to_hi(), format!("({})", call_names.join(", "))),

src/librustdoc/clean/types.rs

@@ -2245,8 +2245,8 @@ impl GenericArgs {
     }
     pub(crate) fn bindings<'a>(&'a self) -> Box<dyn Iterator<Item = TypeBinding> + 'a> {
         match self {
-            &GenericArgs::AngleBracketed { ref bindings, .. } => Box::new(bindings.iter().cloned()),
-            &GenericArgs::Parenthesized { ref output, .. } => Box::new(
+            GenericArgs::AngleBracketed { bindings, .. } => Box::new(bindings.iter().cloned()),
+            GenericArgs::Parenthesized { output, .. } => Box::new(
                 output
                     .as_ref()
                     .map(|ty| TypeBinding {
@@ -2270,8 +2270,8 @@ impl<'a> IntoIterator for &'a GenericArgs {
     type Item = GenericArg;
     fn into_iter(self) -> Self::IntoIter {
         match self {
-            &GenericArgs::AngleBracketed { ref args, .. } => Box::new(args.iter().cloned()),
-            &GenericArgs::Parenthesized { ref inputs, .. } => {
+            GenericArgs::AngleBracketed { args, .. } => Box::new(args.iter().cloned()),
+            GenericArgs::Parenthesized { inputs, .. } => {
                 Box::new(inputs.iter().cloned().map(GenericArg::Type))
             }
         }