Simplify is_box_of_default and is_default_call

Co-authored-by: Samuel Tardieu <[email protected]>

Author: bluebear94

clippy_lints/src/default_box_assignments.rs

@@ -5,7 +5,7 @@ use clippy_utils::ty::implements_trait;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, LangItem};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::{self, GenericArgKind, Ty};
+use rustc_middle::ty::{self, Ty};
 use rustc_session::declare_lint_pass;
 use rustc_span::sym;
 
@@ -38,7 +38,7 @@ impl LateLintPass<'_> for DefaultBoxAssignments {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
         if let ExprKind::Assign(lhs, rhs, _) = &expr.kind {
             let lhs_ty = cx.typeck_results().expr_ty(lhs);
-            if is_box_of_default(lhs_ty, cx) && is_default_call(rhs, cx) && !rhs.span.from_expansion() {
+            if is_box_of_default(cx, lhs_ty) && is_default_call(cx, rhs) && !rhs.span.from_expansion() {
                 span_lint_and_then(
                     cx,
                     DEFAULT_BOX_ASSIGNMENTS,
@@ -64,28 +64,17 @@ impl LateLintPass<'_> for DefaultBoxAssignments {
     }
 }
 
-fn is_box_of_default<'a>(ty: Ty<'a>, cx: &LateContext<'a>) -> bool {
+fn is_box_of_default<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
     if let ty::Adt(def, args) = ty.kind()
-        && cx.tcx.lang_items().get(LangItem::OwnedBox) == Some(def.did())
-        && let Some(inner) = args.iter().find_map(|arg| match arg.kind() {
-            GenericArgKind::Type(ty) => Some(ty),
-            _ => None,
-        })
+        && cx.tcx.is_lang_item(def.did(), LangItem::OwnedBox)
+        && let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default)
     {
-        cx.tcx
-            .get_diagnostic_item(sym::Default)
-            .is_some_and(|id| implements_trait(cx, inner, id, &[]))
+        implements_trait(cx, args.type_at(0), default_trait_id, &[])
     } else {
         false
     }
 }
 
-fn is_default_call(expr: &Expr<'_>, cx: &LateContext<'_>) -> bool {
-    if let ExprKind::Call(func, _args) = expr.kind
-        && is_default_equivalent_call(cx, func, Some(expr))
-    {
-        true
-    } else {
-        false
-    }
+fn is_default_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    matches!(expr.kind, ExprKind::Call(func, _args) if is_default_equivalent_call(cx, func, Some(expr)))
 }