Use more slice patterns inside the compiler

3 files changed, 11 insertions, 12 deletions

diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
index 17439dd3e3e..ed54c0c8662 100644
--- a/compiler/rustc_builtin_macros/src/asm.rs
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -745,10 +745,9 @@ fn expand_preparsed_asm(
             unused_operands.push((args.operands[idx].1, msg));
         }
     }
-    match unused_operands.len() {
-        0 => {}
-        1 => {
-            let (sp, msg) = unused_operands.into_iter().next().unwrap();
+    match unused_operands[..] {
+        [] => {}
+        [(sp, msg)] => {
             ecx.dcx()
                 .struct_span_err(sp, msg)
                 .with_span_label(sp, msg)
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index c8ab8ed681c..c90a9164886 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -378,8 +378,8 @@ impl BlockOrExpr {
                 None => cx.expr_block(cx.block(span, ThinVec::new())),
                 Some(expr) => expr,
             }
-        } else if self.0.len() == 1
-            && let ast::StmtKind::Expr(expr) = &self.0[0].kind
+        } else if let [stmt] = self.0.as_slice()
+            && let ast::StmtKind::Expr(expr) = &stmt.kind
             && self.1.is_none()
         {
             // There's only a single statement expression. Pull it out.
@@ -1273,7 +1273,7 @@ impl<'a> MethodDef<'a> {
                     }
                     FieldlessVariantsStrategy::Default => (),
                 }
-            } else if variants.len() == 1 {
+            } else if let [variant] = variants.as_slice() {
                 // If there is a single variant, we don't need an operation on
                 // the discriminant(s). Just use the most degenerate result.
                 return self.call_substructure_method(
@@ -1281,7 +1281,7 @@ impl<'a> MethodDef<'a> {
                     trait_,
                     type_ident,
                     nonselflike_args,
-                    &EnumMatching(0, &variants[0], Vec::new()),
+                    &EnumMatching(0, variant, Vec::new()),
                 );
             }
         }
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 9c70f7ede8c..306490a4975 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -180,8 +180,8 @@ fn make_format_args(
                     Ok((mut err, suggested)) => {
                         if !suggested {
                             if let ExprKind::Block(block, None) = &efmt.kind
-                                && block.stmts.len() == 1
-                                && let StmtKind::Expr(expr) = &block.stmts[0].kind
+                                && let [stmt] = block.stmts.as_slice()
+                                && let StmtKind::Expr(expr) = &stmt.kind
                                 && let ExprKind::Path(None, path) = &expr.kind
                                 && path.is_potential_trivial_const_arg()
                             {
@@ -196,8 +196,8 @@ fn make_format_args(
                             } else {
                                 let sugg_fmt = match args.explicit_args().len() {
                                     0 => "{}".to_string(),
-                                    _ => {
-                                        format!("{}{{}}", "{} ".repeat(args.explicit_args().len()))
+                                    count => {
+                                        format!("{}{{}}", "{} ".repeat(count))
                                     }
                                 };
                                 err.span_suggestion(