Don't suggest unnameable types in box_default, let_underscore_untyped

clippy_lints/src/box_default.rs

@@ -8,7 +8,9 @@ use rustc_hir::{
     Block, Expr, ExprKind, Local, Node, QPath, TyKind,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
-use rustc_middle::{lint::in_external_macro, ty::print::with_forced_trimmed_paths};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::print::with_forced_trimmed_paths;
+use rustc_middle::ty::IsSuggestable;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
 
@@ -49,7 +51,6 @@ impl LateLintPass<'_> for BoxDefault {
             && path_def_id(cx, ty).map_or(false, |id| Some(id) == cx.tcx.lang_items().owned_box())
             && is_default_equivalent(cx, arg)
         {
-            let arg_ty = cx.typeck_results().expr_ty(arg);
             span_lint_and_sugg(
                 cx,
                 BOX_DEFAULT,
@@ -58,8 +59,10 @@ impl LateLintPass<'_> for BoxDefault {
                 "try",
                 if is_plain_default(arg_path) || given_type(cx, expr) {
                     "Box::default()".into()
-                } else {
+                } else if let Some(arg_ty) = cx.typeck_results().expr_ty(arg).make_suggestable(cx.tcx, true) {
                     with_forced_trimmed_paths!(format!("Box::<{arg_ty}>::default()"))
+                } else {
+                    return
                 },
                 Applicability::MachineApplicable
             );

clippy_lints/src/let_underscore.rs

@@ -2,10 +2,11 @@ use clippy_utils::diagnostics::span_lint_and_help;
 use clippy_utils::is_from_proc_macro;
 use clippy_utils::ty::{implements_trait, is_must_use_ty, match_type};
 use clippy_utils::{is_must_use_func_call, paths};
-use rustc_hir::{ExprKind, Local, PatKind};
+use rustc_hir::{Local, PatKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::subst::GenericArgKind;
+use rustc_middle::ty::IsSuggestable;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::{BytePos, Span};
 
@@ -192,14 +193,12 @@ impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
             if local.pat.default_binding_modes && local.ty.is_none() {
                 // When `default_binding_modes` is true, the `let` keyword is present.
 
-				// Ignore function calls that return impl traits...
-				if let Some(init) = local.init &&
-				matches!(init.kind, ExprKind::Call(_, _) | ExprKind::MethodCall(_, _, _, _)) {
-					let expr_ty = cx.typeck_results().expr_ty(init);
-					if expr_ty.is_impl_trait() {
-						return;
-					}
-				}
+                // Ignore unnameable types
+                if let Some(init) = local.init
+                    && !cx.typeck_results().expr_ty(init).is_suggestable(cx.tcx, true)
+                {
+                    return;
+                }
 
                 // Ignore if it is from a procedural macro...
                 if is_from_proc_macro(cx, init) {

tests/ui/box_default.fixed

@@ -1,6 +1,6 @@
 //@run-rustfix
 #![warn(clippy::box_default)]
-#![allow(clippy::default_constructed_unit_structs)]
+#![allow(unused, clippy::default_constructed_unit_structs)]
 
 #[derive(Default)]
 struct ImplementsDefault;
@@ -35,6 +35,13 @@ fn main() {
     let _more = ret_ty_fn();
     call_ty_fn(Box::default());
     issue_10381();
+
+    // `Box::<Option<_>>::default()` would be valid here, but not `Box::default()` or
+    // `Box::<Option<[closure@...]>::default()`
+    //
+    // Would have a suggestion after https://github.com/rust-lang/rust/blob/fdd030127cc68afec44a8d3f6341525dd34e50ae/compiler/rustc_middle/src/ty/diagnostics.rs#L554-L563
+    let mut unnameable = Box::new(Option::default());
+    let _ = unnameable.insert(|| {});
 }
 
 fn ret_ty_fn() -> Box<bool> {

tests/ui/box_default.rs

@@ -1,6 +1,6 @@
 //@run-rustfix
 #![warn(clippy::box_default)]
-#![allow(clippy::default_constructed_unit_structs)]
+#![allow(unused, clippy::default_constructed_unit_structs)]
 
 #[derive(Default)]
 struct ImplementsDefault;
@@ -35,6 +35,13 @@ fn main() {
     let _more = ret_ty_fn();
     call_ty_fn(Box::new(u8::default()));
     issue_10381();
+
+    // `Box::<Option<_>>::default()` would be valid here, but not `Box::default()` or
+    // `Box::<Option<[closure@...]>::default()`
+    //
+    // Would have a suggestion after https://github.com/rust-lang/rust/blob/fdd030127cc68afec44a8d3f6341525dd34e50ae/compiler/rustc_middle/src/ty/diagnostics.rs#L554-L563
+    let mut unnameable = Box::new(Option::default());
+    let _ = unnameable.insert(|| {});
 }
 
 fn ret_ty_fn() -> Box<bool> {

tests/ui/box_default.stderr

@@ -73,25 +73,25 @@ LL |     call_ty_fn(Box::new(u8::default()));
    |                ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
 
 error: `Box::new(_)` of default value
-  --> $DIR/box_default.rs:41:5
+  --> $DIR/box_default.rs:48:5
    |
 LL |     Box::new(bool::default())
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<bool>::default()`
 
 error: `Box::new(_)` of default value
-  --> $DIR/box_default.rs:58:28
+  --> $DIR/box_default.rs:65:28
    |
 LL |     let _: Box<dyn Read> = Box::new(ImplementsDefault::default());
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<ImplementsDefault>::default()`
 
 error: `Box::new(_)` of default value
-  --> $DIR/box_default.rs:67:17
+  --> $DIR/box_default.rs:74:17
    |
 LL |         let _ = Box::new(WeirdPathed::default());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<WeirdPathed>::default()`
 
 error: `Box::new(_)` of default value
-  --> $DIR/box_default.rs:79:18
+  --> $DIR/box_default.rs:86:18
    |
 LL |             Some(Box::new(Foo::default()))
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<Foo>::default()`

tests/ui/let_underscore_untyped.rs

@@ -54,6 +54,7 @@ fn main() {
     let _ = e();
     let _ = f();
     let _ = g();
+    let closure = || {};
 
     _ = a();
     _ = b(1);