clippy_lints/src/len_zero.rs - rust - Git at Google

 use clippy_config::Conf;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::msrvs::Msrv;
 use clippy_utils::res::{MaybeDef, MaybeTypeckRes};
 use clippy_utils::source::{SpanRangeExt, snippet_with_context};
 use clippy_utils::sugg::{Sugg, has_enclosing_paren};
 use clippy_utils::ty::implements_trait;
 use clippy_utils::{parent_item_name, peel_ref_operators, sym};
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{BinOpKind, Expr, ExprKind, PatExprKind, PatKind, RustcVersion, StabilityLevel, StableSince};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{self, Ty};
 use rustc_session::impl_lint_pass;
 use rustc_span::source_map::Spanned;
 use rustc_span::{Span, Symbol};

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for getting the length of something via `.len()`
     /// just to compare to zero, and suggests using `.is_empty()` where applicable.
     ///
     /// ### Why is this bad?
     /// Some structures can answer `.is_empty()` much faster
     /// than calculating their length. So it is good to get into the habit of using
     /// `.is_empty()`, and having it is cheap.
     /// Besides, it makes the intent clearer than a manual comparison in some contexts.
     ///
     /// ### Example
     /// ```ignore
     /// if x.len() == 0 {
     ///     ..
     /// }
     /// if y.len() != 0 {
     ///     ..
     /// }
     /// ```
     /// instead use
     /// ```ignore
     /// if x.is_empty() {
     ///     ..
     /// }
     /// if !y.is_empty() {
     ///     ..
     /// }
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub LEN_ZERO,
     style,
     "checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for comparing to an empty slice such as `""` or `[]`,
     /// and suggests using `.is_empty()` where applicable.
     ///
     /// ### Why is this bad?
     /// Some structures can answer `.is_empty()` much faster
     /// than checking for equality. So it is good to get into the habit of using
     /// `.is_empty()`, and having it is cheap.
     /// Besides, it makes the intent clearer than a manual comparison in some contexts.
     ///
     /// ### Example
     ///
     /// ```ignore
     /// if s == "" {
     ///     ..
     /// }
     ///
     /// if arr == [] {
     ///     ..
     /// }
     /// ```
     /// Use instead:
     /// ```ignore
     /// if s.is_empty() {
     ///     ..
     /// }
     ///
     /// if arr.is_empty() {
     ///     ..
     /// }
     /// ```
     #[clippy::version = "1.49.0"]
     pub COMPARISON_TO_EMPTY,
     style,
     "checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead"
 }

 pub struct LenZero {
     msrv: Msrv,
 }

 impl_lint_pass!(LenZero => [LEN_ZERO, COMPARISON_TO_EMPTY]);

 impl LenZero {
     pub fn new(conf: &'static Conf) -> Self {
         Self { msrv: conf.msrv }
     }
 }

 impl<'tcx> LateLintPass<'tcx> for LenZero {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::Let(lt) = expr.kind
             && match lt.pat.kind {
                 PatKind::Slice([], None, []) => true,
                 PatKind::Expr(lit)
                     if let PatExprKind::Lit { lit, .. } = lit.kind
                         && let LitKind::Str(lit, _) = lit.node =>
                 {
                     lit.as_str().is_empty()
                 },
                 _ => false,
             }
             && !expr.span.from_expansion()
             && has_is_empty(cx, lt.init, self.msrv)
         {
             let mut applicability = Applicability::MachineApplicable;

             let lit1 = peel_ref_operators(cx, lt.init);
             let lit_str = Sugg::hir_with_context(cx, lit1, lt.span.ctxt(), "_", &mut applicability).maybe_paren();

             span_lint_and_sugg(
                 cx,
                 COMPARISON_TO_EMPTY,
                 lt.span,
                 "comparison to empty slice using `if let`",
                 "using `is_empty` is clearer and more explicit",
                 format!("{lit_str}.is_empty()"),
                 applicability,
             );
         }

         if let ExprKind::MethodCall(method, lhs_expr, [rhs_expr], _) = expr.kind
             && cx.ty_based_def(expr).opt_parent(cx).is_diag_item(cx, sym::PartialEq)
             && !expr.span.from_expansion()
         {
             self.check_empty_expr(
                 cx,
                 expr.span,
                 lhs_expr,
                 peel_ref_operators(cx, rhs_expr),
                 if method.ident.name == sym::ne {
                     "!"
                 } else {
                     Default::default()
                 },
             );
         }

         if let ExprKind::Binary(Spanned { node: cmp, .. }, left, right) = expr.kind
             && !expr.span.from_expansion()
         {
             // expr.span might contains parenthesis, see issue #10529
             let actual_span = span_without_enclosing_paren(cx, expr.span);
             match cmp {
                 BinOpKind::Eq => {
                     self.check_cmp(cx, actual_span, left, right, "", 0); // len == 0
                     self.check_cmp(cx, actual_span, right, left, "", 0); // 0 == len
                 },
                 BinOpKind::Ne => {
                     self.check_cmp(cx, actual_span, left, right, "!", 0); // len != 0
                     self.check_cmp(cx, actual_span, right, left, "!", 0); // 0 != len
                 },
                 BinOpKind::Gt => {
                     self.check_cmp(cx, actual_span, left, right, "!", 0); // len > 0
                     self.check_cmp(cx, actual_span, right, left, "", 1); // 1 > len
                 },
                 BinOpKind::Lt => {
                     self.check_cmp(cx, actual_span, left, right, "", 1); // len < 1
                     self.check_cmp(cx, actual_span, right, left, "!", 0); // 0 < len
                 },
                 BinOpKind::Ge => self.check_cmp(cx, actual_span, left, right, "!", 1), // len >= 1
                 BinOpKind::Le => self.check_cmp(cx, actual_span, right, left, "!", 1), // 1 <= len
                 _ => (),
             }
         }
     }
 }

 impl LenZero {
     fn check_cmp(
         &self,
         cx: &LateContext<'_>,
         span: Span,
         method: &Expr<'_>,
         lit: &Expr<'_>,
         op: &str,
         compare_to: u32,
     ) {
         if method.span.from_expansion() {
             return;
         }

         if let (&ExprKind::MethodCall(method_path, receiver, [], _), ExprKind::Lit(lit)) = (&method.kind, &lit.kind) {
             // check if we are in an is_empty() method
             if parent_item_name(cx, method) == Some(sym::is_empty) {
                 return;
             }

             self.check_len(cx, span, method_path.ident.name, receiver, &lit.node, op, compare_to);
         } else {
             self.check_empty_expr(cx, span, method, lit, op);
         }
     }

     #[expect(clippy::too_many_arguments)]
     fn check_len(
         &self,
         cx: &LateContext<'_>,
         span: Span,
         method_name: Symbol,
         receiver: &Expr<'_>,
         lit: &LitKind,
         op: &str,
         compare_to: u32,
     ) {
         if let LitKind::Int(lit, _) = *lit {
             // check if length is compared to the specified number
             if lit != u128::from(compare_to) {
                 return;
             }

             if method_name == sym::len && has_is_empty(cx, receiver, self.msrv) {
                 let mut applicability = Applicability::MachineApplicable;
                 span_lint_and_sugg(
                     cx,
                     LEN_ZERO,
                     span,
                     format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }),
                     format!("using `{op}is_empty` is clearer and more explicit"),
                     format!(
                         "{op}{}.is_empty()",
                         snippet_with_context(cx, receiver.span, span.ctxt(), "_", &mut applicability).0,
                     ),
                     applicability,
                 );
             }
         }
     }

     fn check_empty_expr(&self, cx: &LateContext<'_>, span: Span, lit1: &Expr<'_>, lit2: &Expr<'_>, op: &str) {
         if (is_empty_array(lit2) || is_empty_string(lit2)) && has_is_empty(cx, lit1, self.msrv) {
             let mut applicability = Applicability::MachineApplicable;

             let lit1 = peel_ref_operators(cx, lit1);
             let lit_str = Sugg::hir_with_context(cx, lit1, span.ctxt(), "_", &mut applicability).maybe_paren();

             span_lint_and_sugg(
                 cx,
                 COMPARISON_TO_EMPTY,
                 span,
                 "comparison to empty slice",
                 format!("using `{op}is_empty` is clearer and more explicit"),
                 format!("{op}{lit_str}.is_empty()"),
                 applicability,
             );
         }
     }
 }

 fn span_without_enclosing_paren(cx: &LateContext<'_>, span: Span) -> Span {
     let Some(snippet) = span.get_source_text(cx) else {
         return span;
     };
     if has_enclosing_paren(snippet) {
         let source_map = cx.tcx.sess.source_map();
         let left_paren = source_map.start_point(span);
         let right_parent = source_map.end_point(span);
         left_paren.between(right_parent)
     } else {
         span
     }
 }

 fn is_empty_string(expr: &Expr<'_>) -> bool {
     if let ExprKind::Lit(lit) = expr.kind
         && let LitKind::Str(lit, _) = lit.node
     {
         let lit = lit.as_str();
         return lit.is_empty();
     }
     false
 }

 fn is_empty_array(expr: &Expr<'_>) -> bool {
     if let ExprKind::Array(arr) = expr.kind {
         return arr.is_empty();
     }
     false
 }

 /// Checks if this type has an `is_empty` method.
 fn has_is_empty(cx: &LateContext<'_>, expr: &Expr<'_>, msrv: Msrv) -> bool {
     /// Gets an `AssocItem` and return true if it matches `is_empty(self)`.
     fn is_is_empty_and_stable(cx: &LateContext<'_>, item: &ty::AssocItem, msrv: Msrv) -> bool {
         if item.is_fn() {
             let sig = cx.tcx.fn_sig(item.def_id).skip_binder();
             let ty = sig.skip_binder();
             ty.inputs().len() == 1
                 && cx.tcx.lookup_stability(item.def_id).is_none_or(|stability| {
                     if let StabilityLevel::Stable { since, .. } = stability.level {
                         let version = match since {
                             StableSince::Version(version) => version,
                             StableSince::Current => RustcVersion::CURRENT,
                             StableSince::Err(_) => return false,
                         };

                         msrv.meets(cx, version)
                     } else {
                         // Unstable fn, check if the feature is enabled.
                         cx.tcx.features().enabled(stability.feature) && msrv.current(cx).is_none()
                     }
                 })
         } else {
             false
         }
     }

     /// Checks the inherent impl's items for an `is_empty(self)` method.
     fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId, msrv: Msrv) -> bool {
         cx.tcx.inherent_impls(id).iter().any(|imp| {
             cx.tcx
                 .associated_items(*imp)
                 .filter_by_name_unhygienic(sym::is_empty)
                 .any(|item| is_is_empty_and_stable(cx, item, msrv))
         })
     }

     fn ty_has_is_empty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, depth: usize, msrv: Msrv) -> bool {
         match ty.kind() {
             ty::Dynamic(tt, ..) => tt.principal().is_some_and(|principal| {
                 cx.tcx
                     .associated_items(principal.def_id())
                     .filter_by_name_unhygienic(sym::is_empty)
                     .any(|item| is_is_empty_and_stable(cx, item, msrv))
             }),
             ty::Alias(ty::Projection, proj) => has_is_empty_impl(cx, proj.def_id, msrv),
             ty::Adt(id, _) => {
                 has_is_empty_impl(cx, id.did(), msrv)
                     || (cx.tcx.recursion_limit().value_within_limit(depth)
                         && cx.tcx.get_diagnostic_item(sym::Deref).is_some_and(|deref_id| {
                             implements_trait(cx, ty, deref_id, &[])
                                 && cx
                                     .get_associated_type(ty, deref_id, sym::Target)
                                     .is_some_and(|deref_ty| ty_has_is_empty(cx, deref_ty, depth + 1, msrv))
                         }))
             },
             ty::Array(..) | ty::Slice(..) | ty::Str => true,
             _ => false,
         }
     }

     ty_has_is_empty(cx, cx.typeck_results().expr_ty(expr).peel_refs(), 0, msrv)
 }
	use clippy_config::Conf;
	use clippy_utils::diagnostics::span_lint_and_sugg;
	use clippy_utils::msrvs::Msrv;
	use clippy_utils::res::{MaybeDef, MaybeTypeckRes};
	use clippy_utils::source::{SpanRangeExt, snippet_with_context};
	use clippy_utils::sugg::{Sugg, has_enclosing_paren};
	use clippy_utils::ty::implements_trait;
	use clippy_utils::{parent_item_name, peel_ref_operators, sym};
	use rustc_ast::ast::LitKind;
	use rustc_errors::Applicability;
	use rustc_hir::def_id::DefId;
	use rustc_hir::{BinOpKind, Expr, ExprKind, PatExprKind, PatKind, RustcVersion, StabilityLevel, StableSince};
	use rustc_lint::{LateContext, LateLintPass};
	use rustc_middle::ty::{self, Ty};
	use rustc_session::impl_lint_pass;
	use rustc_span::source_map::Spanned;
	use rustc_span::{Span, Symbol};

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for getting the length of something via `.len()`
	/// just to compare to zero, and suggests using `.is_empty()` where applicable.
	///
	/// ### Why is this bad?
	/// Some structures can answer `.is_empty()` much faster
	/// than calculating their length. So it is good to get into the habit of using
	/// `.is_empty()`, and having it is cheap.
	/// Besides, it makes the intent clearer than a manual comparison in some contexts.
	///
	/// ### Example
	/// ```ignore
	/// if x.len() == 0 {
	/// ..
	/// }
	/// if y.len() != 0 {
	/// ..
	/// }
	/// ```
	/// instead use
	/// ```ignore
	/// if x.is_empty() {
	/// ..
	/// }
	/// if !y.is_empty() {
	/// ..
	/// }
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub LEN_ZERO,
	style,
	"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for comparing to an empty slice such as `""` or `[]`,
	/// and suggests using `.is_empty()` where applicable.
	///
	/// ### Why is this bad?
	/// Some structures can answer `.is_empty()` much faster
	/// than checking for equality. So it is good to get into the habit of using
	/// `.is_empty()`, and having it is cheap.
	/// Besides, it makes the intent clearer than a manual comparison in some contexts.
	///
	/// ### Example
	///
	/// ```ignore
	/// if s == "" {
	/// ..
	/// }
	///
	/// if arr == [] {
	/// ..
	/// }
	/// ```
	/// Use instead:
	/// ```ignore
	/// if s.is_empty() {
	/// ..
	/// }
	///
	/// if arr.is_empty() {
	/// ..
	/// }
	/// ```
	#[clippy::version = "1.49.0"]
	pub COMPARISON_TO_EMPTY,
	style,
	"checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead"
	}

	pub struct LenZero {
	msrv: Msrv,
	}

	impl_lint_pass!(LenZero => [LEN_ZERO, COMPARISON_TO_EMPTY]);

	impl LenZero {
	pub fn new(conf: &'static Conf) -> Self {
	Self { msrv: conf.msrv }
	}
	}

	impl<'tcx> LateLintPass<'tcx> for LenZero {
	fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
	if let ExprKind::Let(lt) = expr.kind
	&& match lt.pat.kind {
	PatKind::Slice([], None, []) => true,
	PatKind::Expr(lit)
	if let PatExprKind::Lit { lit, .. } = lit.kind
	&& let LitKind::Str(lit, _) = lit.node =>
	{
	lit.as_str().is_empty()
	},
	_ => false,
	}
	&& !expr.span.from_expansion()
	&& has_is_empty(cx, lt.init, self.msrv)
	{
	let mut applicability = Applicability::MachineApplicable;

	let lit1 = peel_ref_operators(cx, lt.init);
	let lit_str = Sugg::hir_with_context(cx, lit1, lt.span.ctxt(), "_", &mut applicability).maybe_paren();

	span_lint_and_sugg(
	cx,
	COMPARISON_TO_EMPTY,
	lt.span,
	"comparison to empty slice using `if let`",
	"using `is_empty` is clearer and more explicit",
	format!("{lit_str}.is_empty()"),
	applicability,
	);
	}

	if let ExprKind::MethodCall(method, lhs_expr, [rhs_expr], _) = expr.kind
	&& cx.ty_based_def(expr).opt_parent(cx).is_diag_item(cx, sym::PartialEq)
	&& !expr.span.from_expansion()
	{
	self.check_empty_expr(
	cx,
	expr.span,
	lhs_expr,
	peel_ref_operators(cx, rhs_expr),
	if method.ident.name == sym::ne {
	"!"
	} else {
	Default::default()
	},
	);
	}

	if let ExprKind::Binary(Spanned { node: cmp, .. }, left, right) = expr.kind
	&& !expr.span.from_expansion()
	{
	// expr.span might contains parenthesis, see issue #10529
	let actual_span = span_without_enclosing_paren(cx, expr.span);
	match cmp {
	BinOpKind::Eq => {
	self.check_cmp(cx, actual_span, left, right, "", 0); // len == 0
	self.check_cmp(cx, actual_span, right, left, "", 0); // 0 == len
	},
	BinOpKind::Ne => {
	self.check_cmp(cx, actual_span, left, right, "!", 0); // len != 0
	self.check_cmp(cx, actual_span, right, left, "!", 0); // 0 != len
	},
	BinOpKind::Gt => {
	self.check_cmp(cx, actual_span, left, right, "!", 0); // len > 0
	self.check_cmp(cx, actual_span, right, left, "", 1); // 1 > len
	},
	BinOpKind::Lt => {
	self.check_cmp(cx, actual_span, left, right, "", 1); // len < 1
	self.check_cmp(cx, actual_span, right, left, "!", 0); // 0 < len
	},
	BinOpKind::Ge => self.check_cmp(cx, actual_span, left, right, "!", 1), // len >= 1
	BinOpKind::Le => self.check_cmp(cx, actual_span, right, left, "!", 1), // 1 <= len
	_ => (),
	}
	}
	}
	}

	impl LenZero {
	fn check_cmp(
	&self,
	cx: &LateContext<'_>,
	span: Span,
	method: &Expr<'_>,
	lit: &Expr<'_>,
	op: &str,
	compare_to: u32,
	) {
	if method.span.from_expansion() {
	return;
	}

	if let (&ExprKind::MethodCall(method_path, receiver, [], _), ExprKind::Lit(lit)) = (&method.kind, &lit.kind) {
	// check if we are in an is_empty() method
	if parent_item_name(cx, method) == Some(sym::is_empty) {
	return;
	}

	self.check_len(cx, span, method_path.ident.name, receiver, &lit.node, op, compare_to);
	} else {
	self.check_empty_expr(cx, span, method, lit, op);
	}
	}

	#[expect(clippy::too_many_arguments)]
	fn check_len(
	&self,
	cx: &LateContext<'_>,
	span: Span,
	method_name: Symbol,
	receiver: &Expr<'_>,
	lit: &LitKind,
	op: &str,
	compare_to: u32,
	) {
	if let LitKind::Int(lit, _) = *lit {
	// check if length is compared to the specified number
	if lit != u128::from(compare_to) {
	return;
	}

	if method_name == sym::len && has_is_empty(cx, receiver, self.msrv) {
	let mut applicability = Applicability::MachineApplicable;
	span_lint_and_sugg(
	cx,
	LEN_ZERO,
	span,
	format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }),
	format!("using `{op}is_empty` is clearer and more explicit"),
	format!(
	"{op}{}.is_empty()",
	snippet_with_context(cx, receiver.span, span.ctxt(), "_", &mut applicability).0,
	),
	applicability,
	);
	}
	}
	}

	fn check_empty_expr(&self, cx: &LateContext<'_>, span: Span, lit1: &Expr<'_>, lit2: &Expr<'_>, op: &str) {
	if (is_empty_array(lit2) \|\| is_empty_string(lit2)) && has_is_empty(cx, lit1, self.msrv) {
	let mut applicability = Applicability::MachineApplicable;

	let lit1 = peel_ref_operators(cx, lit1);
	let lit_str = Sugg::hir_with_context(cx, lit1, span.ctxt(), "_", &mut applicability).maybe_paren();

	span_lint_and_sugg(
	cx,
	COMPARISON_TO_EMPTY,
	span,
	"comparison to empty slice",
	format!("using `{op}is_empty` is clearer and more explicit"),
	format!("{op}{lit_str}.is_empty()"),
	applicability,
	);
	}
	}
	}

	fn span_without_enclosing_paren(cx: &LateContext<'_>, span: Span) -> Span {
	let Some(snippet) = span.get_source_text(cx) else {
	return span;
	};
	if has_enclosing_paren(snippet) {
	let source_map = cx.tcx.sess.source_map();
	let left_paren = source_map.start_point(span);
	let right_parent = source_map.end_point(span);
	left_paren.between(right_parent)
	} else {
	span
	}
	}

	fn is_empty_string(expr: &Expr<'_>) -> bool {
	if let ExprKind::Lit(lit) = expr.kind
	&& let LitKind::Str(lit, _) = lit.node
	{
	let lit = lit.as_str();
	return lit.is_empty();
	}
	false
	}

	fn is_empty_array(expr: &Expr<'_>) -> bool {
	if let ExprKind::Array(arr) = expr.kind {
	return arr.is_empty();
	}
	false
	}

	/// Checks if this type has an `is_empty` method.
	fn has_is_empty(cx: &LateContext<'_>, expr: &Expr<'_>, msrv: Msrv) -> bool {
	/// Gets an `AssocItem` and return true if it matches `is_empty(self)`.
	fn is_is_empty_and_stable(cx: &LateContext<'_>, item: &ty::AssocItem, msrv: Msrv) -> bool {
	if item.is_fn() {
	let sig = cx.tcx.fn_sig(item.def_id).skip_binder();
	let ty = sig.skip_binder();
	ty.inputs().len() == 1
	&& cx.tcx.lookup_stability(item.def_id).is_none_or(\|stability\| {
	if let StabilityLevel::Stable { since, .. } = stability.level {
	let version = match since {
	StableSince::Version(version) => version,
	StableSince::Current => RustcVersion::CURRENT,
	StableSince::Err(_) => return false,
	};

	msrv.meets(cx, version)
	} else {
	// Unstable fn, check if the feature is enabled.
	cx.tcx.features().enabled(stability.feature) && msrv.current(cx).is_none()
	}
	})
	} else {
	false
	}
	}

	/// Checks the inherent impl's items for an `is_empty(self)` method.
	fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId, msrv: Msrv) -> bool {
	cx.tcx.inherent_impls(id).iter().any(\|imp\| {
	cx.tcx
	.associated_items(*imp)
	.filter_by_name_unhygienic(sym::is_empty)
	.any(\|item\| is_is_empty_and_stable(cx, item, msrv))
	})
	}

	fn ty_has_is_empty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, depth: usize, msrv: Msrv) -> bool {
	match ty.kind() {
	ty::Dynamic(tt, ..) => tt.principal().is_some_and(\|principal\| {
	cx.tcx
	.associated_items(principal.def_id())
	.filter_by_name_unhygienic(sym::is_empty)
	.any(\|item\| is_is_empty_and_stable(cx, item, msrv))
	}),
	ty::Alias(ty::Projection, proj) => has_is_empty_impl(cx, proj.def_id, msrv),
	ty::Adt(id, _) => {
	has_is_empty_impl(cx, id.did(), msrv)
	\|\| (cx.tcx.recursion_limit().value_within_limit(depth)
	&& cx.tcx.get_diagnostic_item(sym::Deref).is_some_and(\|deref_id\| {
	implements_trait(cx, ty, deref_id, &[])
	&& cx
	.get_associated_type(ty, deref_id, sym::Target)
	.is_some_and(\|deref_ty\| ty_has_is_empty(cx, deref_ty, depth + 1, msrv))
	}))
	},
	ty::Array(..) \| ty::Slice(..) \| ty::Str => true,
	_ => false,
	}
	}

	ty_has_is_empty(cx, cx.typeck_results().expr_ty(expr).peel_refs(), 0, msrv)
	}