Rollup merge of #128762 - fmease:use-more-slice-pats, r=compiler-errors

Use more slice patterns inside the compiler

Nothing super noteworthy. Just replacing the common 'fragile' pattern of "length check followed by indexing or unwrap" with slice patterns for legibility and 'robustness'.

r? ghost

3 files changed, 7 insertions, 7 deletions

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 1cee82f04ea..95d4509c100 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -944,8 +944,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 // The current method call returns `Result<_, ()>`
                 && self.can_eq(obligation.param_env, ty, found_ty)
                 // There's a single argument in the method call and it is a closure
-                && args.len() == 1
-                && let Some(arg) = args.get(0)
+                && let [arg] = args
                 && let hir::ExprKind::Closure(closure) = arg.kind
                 // The closure has a block for its body with no tail expression
                 && let body = self.tcx.hir().body(closure.body)
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
index 3a082893c5c..f656f9b0e38 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
@@ -73,10 +73,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
             });
 
-            let impl_def_id_and_args = if self_match_impls.len() == 1 {
-                self_match_impls[0]
-            } else if fuzzy_match_impls.len() == 1 {
-                fuzzy_match_impls[0]
+            let impl_def_id_and_args = if let [impl_] = self_match_impls[..] {
+                impl_
+            } else if let [impl_] = fuzzy_match_impls[..] {
+                impl_
             } else {
                 return None;
             };
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index 0d15ef55e24..9269177eb50 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -5300,7 +5300,8 @@ impl<'v> Visitor<'v> for FindTypeParam {
         match ty.kind {
             hir::TyKind::Ptr(_) | hir::TyKind::Ref(..) | hir::TyKind::TraitObject(..) => {}
             hir::TyKind::Path(hir::QPath::Resolved(None, path))
-                if path.segments.len() == 1 && path.segments[0].ident.name == self.param =>
+                if let [segment] = path.segments
+                    && segment.ident.name == self.param =>
             {
                 if !self.nested {
                     debug!(?ty, "FindTypeParam::visit_ty");