Rollup merge of #129969 - GrigorenkoPV:boxed-ty, r=compiler-errors

Make `Ty::boxed_ty` return an `Option`

Looks like a good place to use Rust's type system.

---

Most of https://github.com/rust-lang/rust/blob/4ac7bcbaad8d6fd7a51bdf1b696cbc3ba4c796cf/compiler/rustc_middle/src/ty/sty.rs#L971-L1963 looks like it could be moved to `TyKind` (then I guess  `Ty` should be made to deref to `TyKind`).

5 files changed, 11 insertions, 13 deletions

diff --git a/src/tools/clippy/clippy_lints/src/escape.rs b/src/tools/clippy/clippy_lints/src/escape.rs
index a5da52b0be5..80360697941 100644
--- a/src/tools/clippy/clippy_lints/src/escape.rs
+++ b/src/tools/clippy/clippy_lints/src/escape.rs
@@ -50,7 +50,7 @@ declare_clippy_lint! {
 }
 
 fn is_non_trait_box(ty: Ty<'_>) -> bool {
-    ty.is_box() && !ty.boxed_ty().is_trait()
+    ty.boxed_ty().is_some_and(|boxed| !boxed.is_trait())
 }
 
 struct EscapeDelegate<'a, 'tcx> {
@@ -191,8 +191,8 @@ impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
 impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
     fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
         // Large types need to be boxed to avoid stack overflows.
-        if ty.is_box() {
-            self.cx.layout_of(ty.boxed_ty()).map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
+        if let Some(boxed_ty) = ty.boxed_ty() {
+            self.cx.layout_of(boxed_ty).map_or(0, |l| l.size.bytes()) > self.too_large_for_stack
         } else {
             false
         }
diff --git a/src/tools/clippy/clippy_lints/src/methods/mod.rs b/src/tools/clippy/clippy_lints/src/methods/mod.rs
index d7126990edb..f61bb3a6bf4 100644
--- a/src/tools/clippy/clippy_lints/src/methods/mod.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/mod.rs
@@ -5187,8 +5187,8 @@ impl SelfKind {
         fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
             if ty == parent_ty {
                 true
-            } else if ty.is_box() {
-                ty.boxed_ty() == parent_ty
+            } else if let Some(boxed_ty) = ty.boxed_ty() {
+                boxed_ty == parent_ty
             } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
                 if let ty::Adt(_, args) = ty.kind() {
                     args.types().next().map_or(false, |t| t == parent_ty)
diff --git a/src/tools/clippy/clippy_lints/src/methods/utils.rs b/src/tools/clippy/clippy_lints/src/methods/utils.rs
index 0d2b0a31317..fe860e5ae26 100644
--- a/src/tools/clippy/clippy_lints/src/methods/utils.rs
+++ b/src/tools/clippy/clippy_lints/src/methods/utils.rs
@@ -16,7 +16,7 @@ pub(super) fn derefs_to_slice<'tcx>(
     fn may_slice<'a>(cx: &LateContext<'a>, ty: Ty<'a>) -> bool {
         match ty.kind() {
             ty::Slice(_) => true,
-            ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
+            ty::Adt(..) if let Some(boxed) = ty.boxed_ty() => may_slice(cx, boxed),
             ty::Adt(..) => is_type_diagnostic_item(cx, ty, sym::Vec),
             ty::Array(_, size) => size.try_eval_target_usize(cx.tcx, cx.param_env).is_some(),
             ty::Ref(_, inner, _) => may_slice(cx, *inner),
@@ -33,7 +33,7 @@ pub(super) fn derefs_to_slice<'tcx>(
     } else {
         match ty.kind() {
             ty::Slice(_) => Some(expr),
-            ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
+            _ if ty.boxed_ty().is_some_and(|boxed| may_slice(cx, boxed)) => Some(expr),
             ty::Ref(_, inner, _) => {
                 if may_slice(cx, *inner) {
                     Some(expr)
diff --git a/src/tools/clippy/clippy_lints/src/unnecessary_box_returns.rs b/src/tools/clippy/clippy_lints/src/unnecessary_box_returns.rs
index 3f130bf5a67..14f4aa6676b 100644
--- a/src/tools/clippy/clippy_lints/src/unnecessary_box_returns.rs
+++ b/src/tools/clippy/clippy_lints/src/unnecessary_box_returns.rs
@@ -75,11 +75,9 @@ impl UnnecessaryBoxReturns {
             .instantiate_bound_regions_with_erased(cx.tcx.fn_sig(def_id).skip_binder())
             .output();
 
-        if !return_ty.is_box() {
+        let Some(boxed_ty) = return_ty.boxed_ty() else {
             return;
-        }
-
-        let boxed_ty = return_ty.boxed_ty();
+        };
 
         // It's sometimes useful to return Box<T> if T is unsized, so don't lint those.
         // Also, don't lint if we know that T is very large, in which case returning
diff --git a/src/tools/clippy/clippy_utils/src/ty.rs b/src/tools/clippy/clippy_utils/src/ty.rs
index f80981c11af..585134209ca 100644
--- a/src/tools/clippy/clippy_utils/src/ty.rs
+++ b/src/tools/clippy/clippy_utils/src/ty.rs
@@ -704,8 +704,8 @@ pub fn expr_sig<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<ExprFnS
 
 /// If the type is function like, get the signature for it.
 pub fn ty_sig<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<ExprFnSig<'tcx>> {
-    if ty.is_box() {
-        return ty_sig(cx, ty.boxed_ty());
+    if let Some(boxed_ty) = ty.boxed_ty() {
+        return ty_sig(cx, boxed_ty);
     }
     match *ty.kind() {
         ty::Closure(id, subs) => {